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| Our motor :) |
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| The paper clips are so pretty! |
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| Collection of the passed motors. |
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| Well done, everyone!! |
Thursday, September 30, 2010
Motor building
Today, our class brought together various supplies to build a motor. As others would have been, I was greatly excited by the prospect of building a motor myself. With the excitement, Young and I partnered up to construct a motor. We spent the first 30 minutes hammering our nails into our wood. When Mr. Chung told us that we had 30 minutes to hammer a few nails in, I couldn't really understand why we would need that much time; however, after actually experiencing it, I realized why. We looked for perfect alignment of both sets of the nails, hammered until the nails stood straight, and continued hammering to equalize the height of all four nails involved. After having the hammering done, everything went smoothly. We had our brushes ready, and I thought we were pretty much done if we continued at this speed. I was wrong. The coiling part just got Young and me badly. The sharp tip of the nail kept poking my fingers, making them numb. Not only that, but coiling such a thing copper wire was strenuous. After painful coiling, we finally finished wrapping the copper wire around our commutators. The commutator worked as the instrument that changes the current applied on the copper wire, so that the motor can perform continuous spinning. Our barely made it over the pass line, but I am grateful of the fact that we passed.
Wednesday, September 22, 2010
Right Hand Rules #1 & 2
Right-hand rule #1 (conductors)
Thumb of right hand points in direction of conventional current flow, fingers point in direction of circular magnetic field around conductor.
Right-hand rule #2 (coil)
Curled fingers of right hand point in direction of conventional current flow, thumb points in direction of magnetic field around conductor.
Watch an MIT lecture on this topic of magnetism and right-hand rules:
http://www.youtube.com/watch?v=qqkUeQ0nsF8&feature=related
(the lecturer talks about what we have learned during the first ten minutes of the video)
Thumb of right hand points in direction of conventional current flow, fingers point in direction of circular magnetic field around conductor.
Right-hand rule #2 (coil)
Curled fingers of right hand point in direction of conventional current flow, thumb points in direction of magnetic field around conductor.
Watch an MIT lecture on this topic of magnetism and right-hand rules:
http://www.youtube.com/watch?v=qqkUeQ0nsF8&feature=related
(the lecturer talks about what we have learned during the first ten minutes of the video)
Monday, September 20, 2010
A great educational website
http://www.school-for-champions.com/default.htm
Not only does this website cover the subject of physics, but it also covers chemistry, sports, human behaviour, and so many other interesting topics. The list would be too long to post on the blog (and I'm sure no one will go through the whole list), so I will just leave it up to you to visit the website!
Not only does this website cover the subject of physics, but it also covers chemistry, sports, human behaviour, and so many other interesting topics. The list would be too long to post on the blog (and I'm sure no one will go through the whole list), so I will just leave it up to you to visit the website!
Magnetism - Pages 582 ~ 589
DEFINITIONS
magnetic field - the distribution of a magnetic force in the region of a magnet
test compass - a compass used to check for the presence of a magnetic field
ferromagnetic metals - metals such as iron, nickel, cobalt, or mixtures of these three that attract magnets
domain theory of magnets - "all large magnets are made up of many smaller and flexible magnets that can interact with each other"
dipoles - the small and flexible magnets that make up a large magnet
magnetic domain - the effect produced when dipoles of a magnet line up
Oersted's Principle - "charge moving through a conductor produces a circular magnetic field around the conductor"
right-hand rule - a set of hand signs that allow people to take certain known factors and predict one unknown factor of magnetic forces
electromagnet - a coil of wire around a soft iron core, which uses electric current to produce a magnetic field
INFORMATION
17.1 The Magnetic Force--Another Force at a Distance
- magnetic poles of the same kind repel each other with a force a distance (N and N, S and S)
poles with different labels attract each other with a force at a distance (N and S)
- Earth is like a giant magnet, producing its own magnetic field. It is believed that Earth's magnetic field is produced because of the flow of hot liquid metals inside Earth.
- Iron, nickel, and cobalt, or mixtures of these three are collectively called the ferromagnetic metals, and despite the fact that they are not magnets, they are still attracted by actual magnets. In fact, all magnets appear to be made up of these materials.
- According to the domain theory of magnets, "all large magnets are made up of many smaller and flexible magnets, called dipoles, which can interact with other dipoles close by. If dipoles line up, then a small magnetic domain is produced."
17.2 Electromagnets
- According to Oersted's principle, "charge moving through a conductor produces a circular magnetic field around the conductor."
- Mapping the magnetic field allows people to predict the direction of the electromagnetic force from the current, and there are right-hand rules that will help them do the mapping.
Right-hand rule #1 (RHR#1) for conventional current flow (conductors)
Right-Hand Rule #1 determines the directions of magnetic force, conventional current and the magnetic field. Given any two of theses, the third can be found.
Right-hand rule #2 (RHR#2) for conventional current flow (coils)
Right-Hand Rule #2 determines the direction of the magnetic field around a current-carrying wire and vice-versa
Resources:
http://physicsed.buffalostate.edu/SeatExpts/resource/rhr/rhr.htm
http://www.school-for-champions.com/science/magnetism.htm
magnetic field - the distribution of a magnetic force in the region of a magnet
test compass - a compass used to check for the presence of a magnetic field
ferromagnetic metals - metals such as iron, nickel, cobalt, or mixtures of these three that attract magnets
domain theory of magnets - "all large magnets are made up of many smaller and flexible magnets that can interact with each other"
dipoles - the small and flexible magnets that make up a large magnet
magnetic domain - the effect produced when dipoles of a magnet line up
Oersted's Principle - "charge moving through a conductor produces a circular magnetic field around the conductor"
right-hand rule - a set of hand signs that allow people to take certain known factors and predict one unknown factor of magnetic forces
electromagnet - a coil of wire around a soft iron core, which uses electric current to produce a magnetic field
INFORMATION
17.1 The Magnetic Force--Another Force at a Distance
- magnetic poles of the same kind repel each other with a force a distance (N and N, S and S)
poles with different labels attract each other with a force at a distance (N and S)
- Earth is like a giant magnet, producing its own magnetic field. It is believed that Earth's magnetic field is produced because of the flow of hot liquid metals inside Earth.
- Iron, nickel, and cobalt, or mixtures of these three are collectively called the ferromagnetic metals, and despite the fact that they are not magnets, they are still attracted by actual magnets. In fact, all magnets appear to be made up of these materials.
- According to the domain theory of magnets, "all large magnets are made up of many smaller and flexible magnets, called dipoles, which can interact with other dipoles close by. If dipoles line up, then a small magnetic domain is produced."
17.2 Electromagnets
- According to Oersted's principle, "charge moving through a conductor produces a circular magnetic field around the conductor."
- Mapping the magnetic field allows people to predict the direction of the electromagnetic force from the current, and there are right-hand rules that will help them do the mapping.
Right-hand rule #1 (RHR#1) for conventional current flow (conductors)
Right-Hand Rule #1 determines the directions of magnetic force, conventional current and the magnetic field. Given any two of theses, the third can be found.
Right-Hand Rule #2 determines the direction of the magnetic field around a current-carrying wire and vice-versa
Resources:
http://physicsed.buffalostate.edu/SeatExpts/resource/rhr/rhr.htm
http://www.school-for-champions.com/science/magnetism.htm
Tuesday, September 14, 2010
Resistance ㅡ Ohm's Law and Kirchhoff's Laws
DEFINITIONS
resistance - the ability of a substance to prevent or resist the flow of electrical current
Ohm's law - a law stating that the direct current flowing in a conductor is directly proportional to the potential difference between its ends
- {R = V/I} <-- R = resistance in volts/ampere, which is given the derived unit of ohm (Ω)
resistivity - a measure of how strongly a material opposes the flow of current [unit : ohm metre (Ω m)]
gauge number - the number on a wire that measures activity from a radioactive source
series circuit - a circuit in which loads are connected one after another in a single path
parallel circuit - a circuit in which loads are connected side by side
Kirchhoff's current law - "The total amount of current into a junction point of a circuit equals the total current that flows out of that same junction."
Kirchhoff's voltage law - "The total of all electrical potential decreases in any complete circuit loop is equal to any potential increases in that circuit loop."
conservation of electric charge - a law stating that the quantity of electric charge, the amount of positive charge minus the amount of negative charge in the universe, is always conserved
conservation of energy - a law stating that the total amount of energy in an isolated system remains constant over time, in other words conserved over time
INFORMATION
16.5 Resistance - Ohm's Law
- the amount of current flow in a circuit, or the amount of energy transferred to the destination, depends on two things:
1. the potential difference of the power supply (the amount of push)
2. the nature of the pathway through the loads that are using the electric potential energy
When the pathway becomes more difficult to pass, there is more of a flow of opposition that follows. Ohm's Law also makes intuitive sense if you apply it to the water-and-pipe analogy. If we have a water pump that exerts pressure (voltage) to push water around a "circuit" (current) through a restriction (resistance), we can model how the three variables interrelate. If the resistance to water flow stays the same and the pump pressure increases, the flow rate must also increase; if the pressure stays the same and the resistance increases (making it more difficult for the water to flow), then the flow rate must decrease; and if the flow rate were to stay the same while the resistance to flow decreased, the required pressure from the pump would necessarily decrease.
- In a graph of voltage vs. current, the slope and the V/I ratio represent the resistance of the load because the resistance remains unchanged in the experiment. Having discovered that V/I ratio stays the same for a particular resistor, he came up with the formula of R = V/I, where R is the resistance and given the unit of ohm (Ω).
- It is evident that a thicker wire has a lower resistance than a thinner one because of the the difference in the size of their paths: the broader path in thicker wire makes it easier for current to pass through the load than the narrow path in thinner wire. HOWEVER, there are also other properties of conductors that affect their resistance: its length, cross-sectional area, the material it is made of, and its temperature.
resistance - the ability of a substance to prevent or resist the flow of electrical current
Ohm's law - a law stating that the direct current flowing in a conductor is directly proportional to the potential difference between its ends
- {R = V/I} <-- R = resistance in volts/ampere, which is given the derived unit of ohm (Ω)
resistivity - a measure of how strongly a material opposes the flow of current [unit : ohm metre (Ω m)]
gauge number - the number on a wire that measures activity from a radioactive source
series circuit - a circuit in which loads are connected one after another in a single path
parallel circuit - a circuit in which loads are connected side by side
Kirchhoff's current law - "The total amount of current into a junction point of a circuit equals the total current that flows out of that same junction."
Kirchhoff's voltage law - "The total of all electrical potential decreases in any complete circuit loop is equal to any potential increases in that circuit loop."
conservation of electric charge - a law stating that the quantity of electric charge, the amount of positive charge minus the amount of negative charge in the universe, is always conserved
conservation of energy - a law stating that the total amount of energy in an isolated system remains constant over time, in other words conserved over time
INFORMATION
16.5 Resistance - Ohm's Law
- the amount of current flow in a circuit, or the amount of energy transferred to the destination, depends on two things:
1. the potential difference of the power supply (the amount of push)
2. the nature of the pathway through the loads that are using the electric potential energy
When the pathway becomes more difficult to pass, there is more of a flow of opposition that follows. Ohm's Law also makes intuitive sense if you apply it to the water-and-pipe analogy. If we have a water pump that exerts pressure (voltage) to push water around a "circuit" (current) through a restriction (resistance), we can model how the three variables interrelate. If the resistance to water flow stays the same and the pump pressure increases, the flow rate must also increase; if the pressure stays the same and the resistance increases (making it more difficult for the water to flow), then the flow rate must decrease; and if the flow rate were to stay the same while the resistance to flow decreased, the required pressure from the pump would necessarily decrease.
- In a graph of voltage vs. current, the slope and the V/I ratio represent the resistance of the load because the resistance remains unchanged in the experiment. Having discovered that V/I ratio stays the same for a particular resistor, he came up with the formula of R = V/I, where R is the resistance and given the unit of ohm (Ω).
- It is evident that a thicker wire has a lower resistance than a thinner one because of the the difference in the size of their paths: the broader path in thicker wire makes it easier for current to pass through the load than the narrow path in thinner wire. HOWEVER, there are also other properties of conductors that affect their resistance: its length, cross-sectional area, the material it is made of, and its temperature.
- Resistance in Series:
R = R1 + R2 + R3
General Equation:
R = R1 + R2 + R3 ... + Rx [x = total number of series resistors in the circuit]
Resistance in Parallel:
1/R = 1/R1 + 1/R2 + 1/R3
General Equation
1/R = 1/R1 + 1/R2 + 1/R3 ... + 1/Rx [x = total number of parallel resistors in the circuit]
SUMMARY OF EQUATIONS
1. [R = V/I] -- current, resistance, and electrical caution
R = resistance in ohms (Ω)
V = voltage/potential difference in volts (V)
I = current in amperes (A)
2. [R1/R2 = L1/L2] -- resistance / length
R1, R2 = resistance in ohms (Ω)
L1, L2 = length in given unit (for example, cm, m, or km)
3. [R1/R2 = A2/A1] -- resistance / cross-section area
R1, R2 = resistance in ohms (Ω)
A1, A2 = cross-section area in given unit
4. [R1/R2 = ρ1/ρ2] -- resistance / type of material
R1, R2 = resistance in ohms (Ω)
ρ1, ρ2 = resistivity in ohm metres (Ω m)
5. [R = R1 + R2 + R3 ... + Rx] -- resistance in series circuit
R = total resistance in ohms (Ω)
R1, R2, R3 = resistances at different parts of the circuit, in ohms (Ω)
x = the total number of series resistors in the circuit
6. [1/R = 1/R1 + 1/R2 + 1/R3 ... + 1/Rx] -- resistance in parallel circuit
R = total resistance in ohms (Ω)
R1, R2, R3 = resistances at different parts of the circuit, in ohms (Ω)
x = the total number of parallel resistors in the circuit
For more information on Ohm's Law, click here.
Monday, September 13, 2010
Friday, September 10, 2010
A very helpful website covering topics of electricity, circuits, and more
URL: http://www.allaboutcircuits.com/
I have used this website to get help for previous blog entries, and the pages on the website are very informative and easy to understand.
It covers a broad range of topics, so to anyone having problems getting information about current, circuits, or any other pertinent topics, I would highly recommend this website!
I have used this website to get help for previous blog entries, and the pages on the website are very informative and easy to understand.
It covers a broad range of topics, so to anyone having problems getting information about current, circuits, or any other pertinent topics, I would highly recommend this website!
What is the difference between a parallel circuit and a series circuit?
A parallel circuit and a series circuit are the two basic types of electric circuit that can be found in electrical devices.
In a parallel circuit, there are multiple pathways between the circuit’s beginning and end. As a result, since the current has more than one route to take, the circuit can still function if one path fails. This makes parallel circuits much more fail-resistant than series circuits which is why parallel circuits are common in everyday applications, such as household wiring. Regardless of how many different paths the circuit has, the total voltage stays the same, and all components of the circuit share the same common points. This set of common points is known as electrically common points. Every parallel circuit has two sets of them.
In a parallel circuit, there are multiple pathways between the circuit’s beginning and end. As a result, since the current has more than one route to take, the circuit can still function if one path fails. This makes parallel circuits much more fail-resistant than series circuits which is why parallel circuits are common in everyday applications, such as household wiring. Regardless of how many different paths the circuit has, the total voltage stays the same, and all components of the circuit share the same common points. This set of common points is known as electrically common points. Every parallel circuit has two sets of them.
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| An example of a parallel circuit |
A series circuit is a circuit in which there is only one path from the source through all of the loads and back to the source. This means that all of the current in the circuit must flow through all of the loads. One example of a series circuit is a string of old Christmas lights. There is only one path for the current to flow. Opening or breaking a series circuit such as this at any point in its path causes the entire circuit to "open" or stop operating. That's because the basic requirement for the circuit to operate a continuous, closed loop path is no longer met. This is the main disadvantage of a series circuit. If any one of the light bulbs or loads burns out or is removed, the entire circuit stops operating. Many of today's circuits are actually a combination of elements in series and parallel to minimize the inconvenience of a pure series circuit.
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| An example of a series circuit |
In our textbook, the definitions of the circuits are as such:
series circuit - a circuit in which loads are connected one after another in a single path
parallel circuit - a circuit in which loads are connected side by side
Websites:
Answers to today's questions # 1 ~ 12
Q1. Can you make the energy ball work? What do you think makes the ball flash and hum?
A. Yes, I can make the energy ball work by placing my fingers on both of the metal contacts on the ball. Since our bodies are huge massed of atoms, we can generate electricity. This electricity flowing in my body gets transferred to the metal contacts, resulting in the presence of current electricity. The charges would eventually reach the metal contacts, whose obligation is to absorb the charges and spit them out on to the battery in the ball, and cause the battery to reach its ultimate goal: to make the ball light up and hum.
Q2. Why do you have to touch both metal contacts to make the ball work?
A. I have to touch both metal contacts to make the ball work because for current electricity to take place, there have to be two terminals that will help charges flow continuously.
Q3. Will the ball light up if you connect the contacts with any material?
A. No, the lighting up will happen only when the both contacts are connected to conductors.
Q4. Which materials will make the energy ball work? Test your hypothesis.
A. Materials that can conduct electricity, such as human body and metals, will make the energy ball function. Our group has tested our hypothesis by lighting up the ball with the metal parts on the caps of our pens. The two metal parts have to somehow come in contact with each other, whether it be through directly coming in contact with each other or through having metal parts come in touch with a member's any body part (in this instance, fingers). How human bodies trigger the electricity in the ball to flow has already been answered in questions # 1 and 2.
Q5. This ball does not work on certain individuals - what could cause this to happen?
A. In all people's bodies, there has to exist electricity, or people's bodies will not be function properly due to lack of electrical signals. Therefore, it does not make sense to say that the ball does not work on certain individuals, unless hindrances get involved. If they have something on the part that is in contact with the ball. For example, if they put gloves on and try to make the ball work using their hands, they will witness futility. These impediments will obstruct any electricity to do its job of making the ball work.
Q6. Can you make the energy ball work with all 5 ~ 6 individuals in your group? Will it work with the entire class?
A. Yes, our group made the energy ball work, with every five of the group members involved. We had two individuals each touching one metal contact on the ball, and the other members came in touch by touching each other's finger. When someone pulled his finger our of the "bond", the ball would stop working. Involving the entire class will make it work. In fact, Mr. Chung had given the class a challenge. Everyone engaged in this activity of lighting up two balls, and it had taken us only a few minutes to successfully light them up. This result proves that it is possible to involve every student in the class and make the energy ball light up and emit sound.
Q7. What kind of a circuit can you form with one ball?
A. A series circuit would form. Having one ball, we need to make just one path of current; therefore, a series circuit would be the most appropriate answer.
Q8. Given 2 balls (combine 2 groups): Can you create a circuit where both balls light up? [1/3]
A. Yes, I can create a circuit that lights up both balls. The process of lighting them up follows the same principle as the one mentioned in question #6 ㅡ it is just that one more ball and a few more people have been added into the process.
Q9. What do you think will happen if one person lets go of another person's hand and why? [2/3]
A. In a series circuit, regardless of whom releases his/her hand, one person letting go would ruin the whole process. In a parallel circuit, should one person let go, only one ball would work. (Further information in the next answer.)
Q10. Does it matter who lets go? Try it. [3/3]
A. As I had mentioned in the preceding answer, letting go of another person's hand in a series circuit would cut off the flow and make neither of the balls work, no matter who lets go. This is because a series circuit requires everyone to be connected in a "series", which means that whether the ball would work or not is dependent on the cooperation of every individual involved.On the other hand, if someone, does not matter who, lets go in a parallel circuit, only one ball would work. A parallel circuit allows the current to have more than one route to take, disruption of one route will not affect the flowing via other routes. To give an analogy of each circuit, in a series circuit, a postman has something to deliver to only one house; and in a parallel circuit, the postman has things to deliver to two houses. In a series circuit, if a part of the route gets destroyed, the postman cannot deliver whatever has to be delivered; in a parallel circuit, if one route becomes impassable for whatever reason, the postman can still reach one house.
Q11. Can you create a circuit where only one ball lights (both balls must be included in the circuit)? [1/2]
A. Yes, using the idea of parallel circuit would make it possible. Information in depth can be found from the answer of question #10.
Q12. What is the minimum number of people required to complete this? [2/2]
A. The minimum number of people required to complete the task mentioned in Q11 is 4.
A. Yes, I can make the energy ball work by placing my fingers on both of the metal contacts on the ball. Since our bodies are huge massed of atoms, we can generate electricity. This electricity flowing in my body gets transferred to the metal contacts, resulting in the presence of current electricity. The charges would eventually reach the metal contacts, whose obligation is to absorb the charges and spit them out on to the battery in the ball, and cause the battery to reach its ultimate goal: to make the ball light up and hum.
Q2. Why do you have to touch both metal contacts to make the ball work?
A. I have to touch both metal contacts to make the ball work because for current electricity to take place, there have to be two terminals that will help charges flow continuously.
Q3. Will the ball light up if you connect the contacts with any material?
A. No, the lighting up will happen only when the both contacts are connected to conductors.
Q4. Which materials will make the energy ball work? Test your hypothesis.
A. Materials that can conduct electricity, such as human body and metals, will make the energy ball function. Our group has tested our hypothesis by lighting up the ball with the metal parts on the caps of our pens. The two metal parts have to somehow come in contact with each other, whether it be through directly coming in contact with each other or through having metal parts come in touch with a member's any body part (in this instance, fingers). How human bodies trigger the electricity in the ball to flow has already been answered in questions # 1 and 2.
Q5. This ball does not work on certain individuals - what could cause this to happen?
A. In all people's bodies, there has to exist electricity, or people's bodies will not be function properly due to lack of electrical signals. Therefore, it does not make sense to say that the ball does not work on certain individuals, unless hindrances get involved. If they have something on the part that is in contact with the ball. For example, if they put gloves on and try to make the ball work using their hands, they will witness futility. These impediments will obstruct any electricity to do its job of making the ball work.
Q6. Can you make the energy ball work with all 5 ~ 6 individuals in your group? Will it work with the entire class?
A. Yes, our group made the energy ball work, with every five of the group members involved. We had two individuals each touching one metal contact on the ball, and the other members came in touch by touching each other's finger. When someone pulled his finger our of the "bond", the ball would stop working. Involving the entire class will make it work. In fact, Mr. Chung had given the class a challenge. Everyone engaged in this activity of lighting up two balls, and it had taken us only a few minutes to successfully light them up. This result proves that it is possible to involve every student in the class and make the energy ball light up and emit sound.
Q7. What kind of a circuit can you form with one ball?
A. A series circuit would form. Having one ball, we need to make just one path of current; therefore, a series circuit would be the most appropriate answer.
Q8. Given 2 balls (combine 2 groups): Can you create a circuit where both balls light up? [1/3]
A. Yes, I can create a circuit that lights up both balls. The process of lighting them up follows the same principle as the one mentioned in question #6 ㅡ it is just that one more ball and a few more people have been added into the process.
Q9. What do you think will happen if one person lets go of another person's hand and why? [2/3]
A. In a series circuit, regardless of whom releases his/her hand, one person letting go would ruin the whole process. In a parallel circuit, should one person let go, only one ball would work. (Further information in the next answer.)
Q10. Does it matter who lets go? Try it. [3/3]
A. As I had mentioned in the preceding answer, letting go of another person's hand in a series circuit would cut off the flow and make neither of the balls work, no matter who lets go. This is because a series circuit requires everyone to be connected in a "series", which means that whether the ball would work or not is dependent on the cooperation of every individual involved.On the other hand, if someone, does not matter who, lets go in a parallel circuit, only one ball would work. A parallel circuit allows the current to have more than one route to take, disruption of one route will not affect the flowing via other routes. To give an analogy of each circuit, in a series circuit, a postman has something to deliver to only one house; and in a parallel circuit, the postman has things to deliver to two houses. In a series circuit, if a part of the route gets destroyed, the postman cannot deliver whatever has to be delivered; in a parallel circuit, if one route becomes impassable for whatever reason, the postman can still reach one house.
Q11. Can you create a circuit where only one ball lights (both balls must be included in the circuit)? [1/2]
A. Yes, using the idea of parallel circuit would make it possible. Information in depth can be found from the answer of question #10.
Q12. What is the minimum number of people required to complete this? [2/2]
A. The minimum number of people required to complete the task mentioned in Q11 is 4.
Thursday, September 9, 2010
What is the centre of gravity?
The centre of gravity is the point at which the whole weight of an object can be considered to act and, thus, at which all parts of an object are in balance. The position of the centre of gravity varies according to the shape of the object. In objects with a regular shape, the centre of gravity coincides with its geometric centre. In objects with an irregular and variable shape (as in the human body), the centre of gravity cannot be defined easily and changes with every change in position of the body; it may not even lie within the physical substance of the body. The centre of gravity of a projectile in flight follows a fixed path, but body movements may raise or lower the body parts around the centre of gravity. In this way, it is possible to jump different heights even though the centre of gravity reaches the same height.
NOTE: The term centre of mass is often used interchangeably with centre of gravity, but they are physically different concepts. They happen to coincide in a uniform gravitational field, but where gravity is not uniform, centre of gravity refers to the mean location of the gravitational force acting on a body.
Websites:
http://en.wikipedia.org/wiki/Center_of_mass
http://www.grc.nasa.gov/WWW/K-12/airplane/cg.html
http://www.answers.com/topic/center-of-gravity
NOTE: The term centre of mass is often used interchangeably with centre of gravity, but they are physically different concepts. They happen to coincide in a uniform gravitational field, but where gravity is not uniform, centre of gravity refers to the mean location of the gravitational force acting on a body.
Websites:
http://en.wikipedia.org/wiki/Center_of_mass
http://www.grc.nasa.gov/WWW/K-12/airplane/cg.html
http://www.answers.com/topic/center-of-gravity
What makes a tall structure stable?
After having scrutinized many tall structures, I have discovered that the key factor in constructing a tall structure is the firmness of the base. A tall structure always has a very large, heavy, and strong base that will support the weight of the top parts of the structure. For instance, the tallest building in the world, Burj Khalifa in Dubai, has a very rigid, strong base that holds up 828m of height. Moreover, most tall skyscrapers are constructed in a way that the circumference or the perimeter of the building descend as the building rises. This structure of gradually descending in diameter or perimeter helps lessen the burden of the base because each part is built bigger that the upper part so that the below part can support the weight of the upper part. There are many types of structure with which many tall structures are designed. One of the common type is a hyperboloid structure. Hyperboloid structures are superior in stability towards outside forces than "straight" buildings, but have shapes often creating large amounts of unusable volume (low space efficiency) and therefore are more commonly used as a purpose driven structure, such as water towers (to support a large mass), cooling towers, and aesthetic features.
Websites:
http://en.academic.ru/dic.nsf/enwiki/2022226
http://www.globalarchitectsguide.com/library/Hyperboloid-structure.php
http://science.howstuffworks.com/engineering/structural/skyscraper.htm
http://en.wikipedia.org/wiki/Skyscraper
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| Burj Khalifa |
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| World's First Hyperboloid Structure, 1896 |
Websites:
http://en.academic.ru/dic.nsf/enwiki/2022226
http://www.globalarchitectsguide.com/library/Hyperboloid-structure.php
http://science.howstuffworks.com/engineering/structural/skyscraper.htm
http://en.wikipedia.org/wiki/Skyscraper
The Physics of Tall Structures: Guangzhou TV & Sightseeing Tower
Another gargantuan structure is to be introduced to us soon. It is taller than Canada's CN Tower, and its name is Guangzhou TV & Sightseeing Tower, also called Canton Tower. Guangzhou, China is a city that will host the 2010 Asian Games. Standing 610m tall, almost 60m taller than CN Tower, Canton Tower is currently under construction and due to be completed in late 2010. The most notable feature of this enormously tall tower is the combination of column rings and diagonals that make people think about spider webs. Not only do they contribute to the dynamic look of the tower, but they are also important in the physics of Canton Tower. These immense layers of steel make up the lattice structure that the tower has. (A lattice structure derives its strength from its double curvature.) This hyperboloid structure of Canton Tower derives its hyperboloid geometry from the two ellipses, one at foundation level and the other at an imaginary horizontal plane just above 450 metres. The tightening caused by the rotation between the two ellipses forms the characterizing "waistline" of the tower, and a densification of material. This means that the lattice structure, which at the bottom of the tower is porous and spacious, becomes denser at waist level. The waist itself is tightened, like a twisted rope; further up the tower the lattice opens again, accentuated here by the tapering of the structural column-tubes. The base of the structure must not be forgotten. The core of Canton Tower consists of a concrete elliptical shaft with a short and long diameter of 15.6m and 18.6m respectively, that has been constructed with the help of a sliding formwork.
Informative Websites:
http://en.wikipedia.org/wiki/Guangzhou_TV_%26_Sightseeing_Tower
http://gztvtower.info/
http://www.gztvtower.info/03b%20Engineering.htm
Informative Websites:
http://en.wikipedia.org/wiki/Guangzhou_TV_%26_Sightseeing_Tower
http://gztvtower.info/
http://www.gztvtower.info/03b%20Engineering.htm
Challenge: Highest Structure
The challenge that we were given yesterday was very interesting. Mr. Chung separated the class into 8 groups and provided us with 5 sheets of newspaper and some masking tape. Our objective was to build the highest structure with the given materials. Jacqueline, Juliet, and I sat at the table and put our heads together to discuss about the physics our structure should have. After a few minutes, Juliet came up with the idea of making a triangular prism base which later developed into a square based pyramid. Each of us took a sheet of paper, cut it in half, and rolled the paper in such a way that it would make a long, firm leg of the base. Our group displayed great teamwork, listening to each other's opinions. However, the flaw with our structure was that we had not thought about the weight distribution of the erect pieces of newspaper. We rolled every piece the same size and the same thickness. Furthermore, our most top part was too heavy in comparison to the other pieces of newspaper supporting the top. In the end, our structure unfortunately collapsed; nevertheless, Mr. Chung complimented the architecture of our structure, and that was enough to make us feel good. From this activity, I have learned that all calculations must be precise in physics. The miscalculation we had made with the top pieces rendered our impeccable base, I would say, powerless. Although it would have been much better if our structure actually stood with rigidity, I value the experience and the lesson that I have attained from this activity.
 |
| Our fallen structure... But it's okay :). |
Wednesday, September 8, 2010
Blog 1: Notes on Current Electricity (pp. 544 ~ 552)
DEFINITIONS
electric current - a flow of charge, measured in amperes
current - the total amount of charge moving past a point in a conductor, divided by the time taken
- {I = Q/t} <-- I = current in amperes (A), Q = charge in coulombs (C) , t = time in second
ampere (A) - the base unit for current; equivalent to one coulomb per second [C/s]
coulomb (C) - the base unit for electric charge
conventional current - the model of positive charge flow
- http://www.youtube.com/watch?v=Y7Uqe6DyoRU [explanation]
ammeter - a current-measuring device
direct current (DC) - an electric current flowing in one direction only
load - a device that converts electric energy to other forms of energy
alternating current (AC) - an electric current that reverses direction in a circuit at regular intervals
circuit - the path of electric current flow from and to the power supply
electrical potential energy - energy stored when static electric charges are held a certain distance apart
electrical potential difference (V), or voltage - the electric potential energy for each coulomb of charge in a circuit
- {V = E/Q} <-- E is the energy required to increase the electric potential of a charge, Q
voltmeter - an instrument for measuring potential differences in volts
parallel circuit - a circuit in which loads are connected side by side
INFORMATION
16.2 Current
- What happens in an electric circuit:
1. Electrons are provided with energy by an energy source.
2. Conductors transport the electrons to the load (i.e. light bulb).
- Conventionally, it was believed that current flow moves from the positive terminal to the negative terminal of any power supply. Although it is actually the electrons that are involved in current flows, the fact that positive charge flowing in one direction is mathematically same as the negative charge flowing in the opposite direction makes in which direction does the current flow move not matter. However, many people working in the field of electricity today still follow the conventional way of perceiving that it is the positive charge that flows in a current, and this model of positive charge flowing in a current is called conventional current. The model of negative charge flowing in a current is called electron flow.
electric current - a flow of charge, measured in amperes
current - the total amount of charge moving past a point in a conductor, divided by the time taken
- {I = Q/t} <-- I = current in amperes (A), Q = charge in coulombs (C) , t = time in second
ampere (A) - the base unit for current; equivalent to one coulomb per second [C/s]
coulomb (C) - the base unit for electric charge
conventional current - the model of positive charge flow
- http://www.youtube.com/watch?v=Y7Uqe6DyoRU [explanation]
ammeter - a current-measuring device
direct current (DC) - an electric current flowing in one direction only
load - a device that converts electric energy to other forms of energy
alternating current (AC) - an electric current that reverses direction in a circuit at regular intervals
circuit - the path of electric current flow from and to the power supply
electrical potential energy - energy stored when static electric charges are held a certain distance apart
electrical potential difference (V), or voltage - the electric potential energy for each coulomb of charge in a circuit
- {V = E/Q} <-- E is the energy required to increase the electric potential of a charge, Q
voltmeter - an instrument for measuring potential differences in volts
parallel circuit - a circuit in which loads are connected side by side
INFORMATION
16.2 Current
- What happens in an electric circuit:
1. Electrons are provided with energy by an energy source.
2. Conductors transport the electrons to the load (i.e. light bulb).
3. The electrons get transported back to the energy source to be re-energized.
- Conventionally, it was believed that current flow moves from the positive terminal to the negative terminal of any power supply. Although it is actually the electrons that are involved in current flows, the fact that positive charge flowing in one direction is mathematically same as the negative charge flowing in the opposite direction makes in which direction does the current flow move not matter. However, many people working in the field of electricity today still follow the conventional way of perceiving that it is the positive charge that flows in a current, and this model of positive charge flowing in a current is called conventional current. The model of negative charge flowing in a current is called electron flow.
- Frequently used symbols in circuit drawings:
(For more symbols, visit http://www.kpsec.freeuk.com/symbol.htm)
- Pertinent to the measurement of current:
- Pertinent to the measurement of current:
- ammeter: a device that measures current; must display excellence in conducting so that it does not affect the process of measuring current
- circuit: the path that carries electric current flow from and to the power supply; required for any electrical device to work properly
16.3 Electrical Potential
- Electrical potential energy is the energy stored when static electric charges are held a certain distance apart. In order for the electrical potential energy of each coulomb of charge to increase, some kind of work has to be done by the power supply. The energy starts to decrease as the charge begins to flow through the load.
- The equation for the energy transferred by charge flow:
{E = VIt} E = energy (in Joules, J), V = potential energy (in volts, V), I = current (in amperes, A) t = time (in seconds, s)
- http://www.youtube.com/watch?v=elJUghWSVh4 [explanation]
- http://www.youtube.com/watch?v=elJUghWSVh4 [explanation]
- A voltmeter is utilized to measure the potential difference between two points. One of the important things to remember is to make sure that the voltmeter and the load are connected side by side, which will help compare the potential before and after the load. The other thing is that the voltmeter must be poorer in the ability to conduct that the connected load, so that the measurement by the voltmeter will not have much effect on the flowing of the current in the circuit.
SUMMARY OF EQUATIONS
1. [ I = Q/t ] -- current and charge
I = current in amperes (A),
Q = charge in coulombs (C) ,
t = time in second
2. [ V = E/Q ] -- potential difference and energy
V = electric potential difference (in volts, V)
E = energy required to increase the electric potential of a charge (in joules, J)
Q = charge carrying electric potential energy (in coulombs, C)
3. [ E = VIt ] -- electrical energy, and potential difference and energy
E = energy (in joules, J)
V = electric potential difference (in volts, V)
I = current (in amperes, A)
t = time (in seconds, s)
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