The Top Ten Things of Physics

Inertia

an object's non-wanting to change states (is measured by an object's mass). An example of inertia is the tablecloth trick

Ohm's Law

Ohm's law has to do with resistance. V=IR is the equation for Ohm's law. V= voltage, I= current, and R= resistance.

Units for V, I and R

Newton's 1st Law

An object at rest tends to stay at rest and an object in motion tends to stay in motion unless acted upon by an outside force.

Newton's 2nd Law

 acceleration is directly proportional to force, and is inversely proportional to mass. F=ma

Newton's 3rd Law

 “every action has an equal and opposite reaction.”

Action Reaction Pair: Hammer pushes nail down, Nail pushes hammer up

Speed and Velocity

You can accelerate while keeping the same speed only when going in a circle without changing speed. Cannot have changing speed and have constant velocity. Difference between velocity and speed is that v requires a specific direction and speed does not

Work/Power

For work to happen, force and distance must be PARALLEL!!
Example problem:

Equation: Work=(force)(distance)

Units: Joules (J)

Equation: Power=work/time

Units: Watts

If a 600N person walks up stairs that are 4 meters high, how much work is done?

Work=F*d

Work=600N*4m

Work=2400J

When is there more work? When a person goes up the stairs to third or when the elevator carries them to third?

The work required is the same. The upward force against gravity (or weight) is the same, and the distance that is parallel to that force (height) is the same, therefore work is the same. Horizontal distance does not matter because it is perpendicular to the upward force, and therefore contributes nothing to the work done.

When considering work, only the height matters.

Work happens to an object when force is exerted on that object over a distance. The equation for work is work=force*time, and it is measured in m/s or Joules. For there to be work, the force and distance must be parallel. In this example, the person's wright, or force, is vertical, and therefore for there to be work, the distance must be vertical as well. Work does not happen when the distance is perpendicular to the force, or when there is no distance.

If the force of the person is 4N, and the staircase is 15m tall, how much work will there be? 

work=force*distance

        = 4N*15m

work= 60 Joules

Power is how quickly work is done. The equation for power is Power=(work)/(time) and is measured in Watts.

If it takes the person 10 seconds to reach the top, how much power is exerted?

Power=(work)/(time)

=60J/10s

Power=6 Watts

Coulomb's Law

Coulomb's law states that the electrical force between two charged objects is directly proportional to the product of the quantity of charge on the objects and inversely proportional to the square of the separation distance between the two objects.

Torque 

Torque is a measure of how much a force acting on an object causes that object to rotate. Torque is equal to the force multiplied by the lever arm. Torque IS NOT equivalent to force! Lever arm is the distance from the axis to the center of gravity. 

Conservation of Momentum

Individual objects can change their momentum, but systems cannot

Ptotal before=Ptotal after

Together in the Beginning:

m_av_a+m_bv_b = m_av_a+m_bv_b

Together in the Ending:

m_av_a+m_bv_b=m_a+bv_ab

Generator

Magnetism is caused by moving charges. By moving the magnets in circles in between the coils of wire, the change in magnetic field needed to induce voltage in the coils is created. This results in AC output. This change of mechanical energy into electric energy is what makes the wind turbine a generator. Notice that I said "generator" and not "motor." There is a distinct difference between these two: motors take electrical energy and turn it into mechanical, while generators take mechanical energy and turn it into electrical. 

Materials used:

4 90-degree elbow PVC fittings, 3 PVC T-fittings ~5 ft. of straight PVC pipe, One large T-fitting with a diameter of at least 2 in. This will house the coils and shaft. At least 2 dowels, 3/8" diameter each (or whatever size you can drill a hole for) 2 PVC end-caps for the generator housing. Solid. You'll drill appropriately sized holes depending on your dowel size later. A small wooden wheel, like you might see on a toy car, to serve as the hub. This is what the propeller blades will be attached to on the outside of the pipe. Several small wooden disks to put your magnets on to. At least 12' of copper wire Some cardboard or other light-weight material to build your blades with. Electric tape, hot glue, sharpies, and any other small supplies you might need when building. Various power tools, most importantly a drill, and a voltmeter.

Side shot of our generator

Here is the inside shot of our generator

 Here is a sketch of the magnet placement and orientation, coils

Here is a sketch of our turbine/generator

On our first try, our generator induced a voltage, so not much difficulty was had there. However, making the generator was more difficult. At one point, someone took our 'magnet wheel' so we had to make a whole new rod, which was more annoying than hard, but it made us take longer to create the generator. We also had trouble putting the generator together. We knew what it had to look like, but we tended to make things more difficult for ourselves by focusing on potential problems that we had not yet encountered. I think it would have gone a lot faster if we had just tested it a bunch before deciding if something was a problem or not.

1.     Resistance

On the wire connecting the coil to the alligator clips

Friction inside the rotating piece

2.     Magnet Placement

The closer the magnet without touching the coil the higher voltage output induced

3.     Coil Strength

The thicker the coil, the stronger the coil. 

The thicker your coil is the higher voltage output it induces.

Motor

Function of each material:

• Loop of Copper wire: Conductor and turbine
• Battery: Provides current flow that allows the magnetic force to influence the wire loop.
• Magnet: provides a magnetic field and therefore a force on the current running through the wire, causing it to spin from the torque applied to the loop.
• Paper clips: hold up the motor coil and allow the current to flow from the battery to the coil.
• Rubber bands/electrical tape: holds the motor together
• Wooden Block: acts as a support for the motor

Why we scraped the armature in a specific way:

We needed the motor to be spinning in a constant direction for it to work, instead of a back-and-forth motion. In order to accomplish this, we had to scrape the wire. We needed the current to flow only when the loop was oriented in a specific way, and not the other. In order to make the motor run properly, we needed the current to flow while the loop was turning in one direction. This would need to happen without causing the loop to turn in the other direction because this would be counter productive.

Why the motor runs:

The motor was able to turn because of the magnetic pull created by the magnet. All magnetism is caused by moving charges. Because of this, in a magnetic field, moving charges are affected by the magnetic force; if the charges are moving perpendicularly to the field, the force is even greater. Therefore, since the motor coil is oriented perpendicularly to the magnet (the coil must be vertical), the magnetic force acting on the charges moving through it is even greater, and the force (which has an upward direction) also acts on the coil itself. Since the sides of the wire are pushed in opposite directions, the wire rotates. When the wire flips and the current is still going in different directions, the magnetic field continues to act on it unless affected by an outside force.

What the motor can be used for:

Unfortunately this motor cannot be used for anything, for it only has enough force to overcome its own friction.  This can however, potentially be used to:

• Entertain your friends
• Impress your physics teacher (**hint**)
• Look cool

Charges and Electricity Reflection

Charges and Polarization including Coulomb's law

Coulomb's Law

F=k(q1q2/d2)

Why does your hair stand up when you take off a hat?

Hat and hair charged by friction. The like charges repel each other and make the hair on your head stand up

Induction? Other ways to charge things?

Induction steals the electrons from an object and makes the object positively charged. Friction and contact are the other ways of charging.

The Difference Between AC and DC

AC stands for 'alternating current'. This means that the current will alternate directions.
DC stands for 'direct current'. This means that the current will keep the same direction throughout.

What is Voltage?

Potential Difference.

Change in PE/ charge

V=(change in PE)/q

Units
Volts (V) = Joules/Coulomb

Energy given to each Coulomb of charged, measured across two points.

What is current?

current is the flow of charge

Units
Amps (A)= Coulombs/second

Current goes through the circuit

What is Resistance?

Resistance is the resistance to the flow of charge.

Unit
Ohms (omega symbol)

Things to Remember:

The electrons that flow are already in the circuit. The actual speed of electrons is extremely slow (think snail's pace).

The Energy/Electric Field travels at neat the speed of light (NOT the electrons themselves... REMEMBER!!! Snail's pace!!)

When something is charged, it means that there is a 'imbalance of protons vs. electrons. To charge an object, charges must be transferred.'

There are 3 methods of charging:

1.) Contact

2.) Friction

3.) Induction

When something is Polarized it means that the the charges within an object have rearranged themselves and that the Net charge still equals zero. This does not mean that the object is now charged.

Electronic Shielding 

(Electric field/ Electric force inside a conductor=0)

Ohm's Law is V=IR

Coulomb's Law

F=k(q1q2/d*2)

The changes in distance affect changes in force shown by:

2d=1/4F and 1/2d=4F

Power=VI

Different filaments have different resistances. The resistance of something can increase in three ways:

1.) longer

2.) thinner

3.) both longer and thinner

What was difficult for me this unit was my organization, or more realistically the lack-there-of. my non-existent organization this unit is making my efforts in studying harder and harder. Next unit, I really need to make a designated binder to keep my quizzes, notes, and handouts in. My poor organization skills are going to kill my grade.

http://goblues.org/faculty/lawrencel/files/2012/08/ONQ-6-2-Answers1.pdf

http://goblues.org/faculty/lawrencel/files/2012/08/ONQ-6-1-Answers.pdf

Ohm's Law

This cartoon helps me remember that Ohm's law has to do with resistance. V=IR is the equation for Ohm's law. V= voltage, I= current, and R= resistance.

Units for V, I and R

The Filament in a light bulb is what gives resistance. The thinner, longer or both thinner and longer the filament is, the more resistant it will be. Resistance also increases the hotter it gets.

Voltage Resource

In this video, the person speaking makes clear some very important points about voltage.

• V= Potential Energy/q
• When you are dealing with volts, you are specifically dealing with energy
• and it is energy per charge
• 1 Volt= 1 J/C
• deals with 2 points

I really liked how he said "when we push, from A to B, we are exerting a force through a distance... We are expending energy, and the energy that we expend goes into potential energy and stored as electrical potential energy... There is more Potential Energy at point B then it had at point A." This was really helpful to hear and see him drawing it out. His comparison between gravity and electrical current was very helpful as well (when he is talking about the toaster). I wish he did more with solving problems, though. Pretty helpful, though, with getting the main ideas down.

Mousetrap Car Lab

This car made 2nd place in our class and 8th out of 18 cars with a time of 3.72 seconds.

Newton's 1st Law of Motion:

An object at rest, tends to stay at rest and an object in motion tends to stay in motion unless acted upon by an outside force.

Applied:

The mousetrap car will stay at rest unless triggered. The mousetrap in motion will continue to move unless affected by an outside force. The outside force of friction between the wheels and the floor caused the car to slow down and eventually stop. 

Newton's 2nd Law of Motion:

Force is directly proportional to acceleration, and indirectly proportional to the mass of an object.

Applied:

We purposefully made our car have less mass because the less mass, the force will cause a greater acceleration to occur. 

Newton's 3rd Law of Motion:

For every action, there is an equal and opposite reaction.

Applied:

Wheels push backward on ground, ground pushes forward the wheels. String pulls axle, axle pulls string. Axle spins wheels, wheels spin axle. 

Two types of friction present:

1. Static
2. Kinetic

Static friction is the type of friction that keeps and object from moving. This would occur when the mousetrap car would not move.

Kinetic Friction is the type of friction that occurs when an object is moving. This would occur when the mousetrap car was in motion.

In regards to friction, my partner and I encountered a problem where the car would not move very far, due to a lack of friction. We fixed this by adding balloons to the rear wheels which gave the wheels more friction, but also more traction so that they would be able to move the car. 

My partner and I found a model where the car had 4 wheels, and thought that that would be a good idea. Using 4 CD's, this made for an easy configuration. The smaller the wheel, the less tangential velocity it has, so using CD's we were able to get a lager tangential velocity than we would have if we used bottle caps (as some other people did). 

Energy can neither be created nor destroyed. This means that energy can never be lost, just transformed into something else. When our car slowed down, energy was transformed into either sound or heat (another form it could take when 'energy is lost' is light, but that did not apply to our car). The car's potential energy can never be greater than what it had in the beginning, which will be the same amount of kinetic energy for the car. 

At first, our lever arm was as long as the distance between the bar of the trap to the back axle. This was a problem because once it unwound from the axle, it would stop the car. By lengthening the lever arm, we found a solution for that problem, but by increasing the lever arm, we lessened the force which meant that our car would go slower. 

By using a CD, rather than a hoop, there was less rotational inertia for our wheels, because the mass was closer to the axis of rotation than the hoop's mass would have been. 

We can't calculate the potential energy that was stored in the spring or the kinetic energy, nor the amount of work the spring did not the car, nor the force the spring exerted on the car to accelerate the car.

REFLECTION:

Our final design was very similar to our original plan. One change we made was instead of using soda-can-taps to keep the front wheels in place, we used zip-ties. The zip-ties were better to use because they were more predictable, and were easier to adjust. Another change was that instead of using balloons to keep the front wheels attached to the axle, we used electrical tape. This was better because the electrical tape was a smoother surface which enabled us to put the wheels where we wanted to and kept them in that place (but also allowed for changes if we needed to). The electrical tape did not completely solve the problem of keeping the wheels centered, but it was much better than the balloons we were using. 

One major problem we encountered was our car stopping because the lever arm was too short. We solved this by increasing the length of the sting used for our lever arm. Another problem we had was keeping the wheels where we needed them. We originally used balloons to keep the front wheels attached to the front axle, but they would not keep the wheels where we needed them, causing the car to run into the wall a lot. By replacing the balloons with electrical tape, this enabled us to more predictably adjust the wheels and keep them where we needed them to be.

If I was to do this project again, I would spend more time on the length of the lever arm. I noticed that by the time the car slowed to a stop, there was still extra string. I would have shortened the lever arm, making the force exerted greater, as well as the acceleration.