The Top Ten Car Rules of Physics

Physics Rules of The Road

Everything about cars involves several aspects of physics. 

1.First we must talk about some safety guidelines. When a person is driving along in a car, they must wear a seat belt! This is because when a person is in a car, the car and the person are moving forward together. When the car comes to a stop the person will not stop and continue to move. We know this because of Newton's First Law which states that an object in motion or an object at rest will remain doing so unless acted upon by an outside force. In other words, objects like to be lazy and continue in the motion they are already in (inertia). So when the car stops and the person keeps moving, they very easily fly forward. However, seat belts prevent this from happening. Seat belts are able to stop the person when the car stops. This also goes for unfortunate accidents such as leaving your cup of Joe on the roof of your car. When this sugared and sweetened cup is at rest on top of the car and the car takes off, the coffee will fall. Because Newton's first law tells us that an object in motion 
or an object at rest will remain doing so unless acted upon by an outside force, we know that the while the car starts to move, the coffee will remain motionless, causing an lack of caffeine to start your morning. 

2. So how do airbags keep you from getting hurt?
Lets first establish that Momentum is defined as the product if the mass of an object and its velocity.
P= momentum
m= mass
v= velocity
P=mv
The change in momentum is formatted as Δp= pfinal-pinitial 
-A moving object can have a large momentum if either its mass or its velocity are large. 
-In order to have momentum you must be in motion.
Impulse is a force exerted for a certain amount of time. 
Therefor, Impulse is force x time interval.
And impulse is then defined as Ft.
Impulse changes momentum- the greater the impulse exerted on something, the greater will be the change in momentum. 
Impulse= change in momentum
Ft= Δ(mv)
J= FΔt

3. The law of conservation of energy is the law that states  "The total amount of energy in a system remains constant (is conserved), although energy within the system can be changed from one form to another or transferred from one object to another, energy cannot be created or destroyed. It can only be transformed." Before the car starts to move, there is potential energy, once it does, it becomes kinetic energy (energy of movement).
It also means that work in= work out.
Work= force x distance
Machines are able to decrease the amount of force needed for work to happen. (pulleys,ramps)
P=mv
ΔP= pfinal-pinitial
ΔP is the same regardless if you stop quickly or slowly. 
You will go from moving to not moving not moving no matter how you stop. Therefor, the change in momentum is the same no matter how you stop. J= ΔP 
J= FΔt 
J remains the same.
J is the same whether or not there is an impulse.
The airbag increases the time of the impulse and increase the distance between your body and the steering wheel. Since work stays the same, the force must compensate and decrease. Without an airbag, work is equal to a large force and a small distance. 
With an airbag, work is equal to a small force and a large distance. Less force = less injury!


4. Newton's second law states that acceleration is directly proportional to force and inversely proportional to mass.
 a=F/m 
 Acceleration is the change in velocity over a certain time interval
(a= change in velocity/ time interval)
(a=Δ v/t)
Constant acceleration is when you gain the same amount of speed (m/s^2) per second. 
You can find how fast a car is going at a constant acceleration by using this formula: v=at
And you can find the distance of a car moving at a constant acceleration by this formula: d=1/2at^2

If a train runs into a parked car, they both will experience the same force. Neither one exerts a larger force on the other. However, they will experience different accelerations. The one with the smaller mass (parked car), will experience a greater acceleration than the train. This is because mass and acceleration are inversely proportional to acceleration. 


5. So let's explore this concept. When a car hits another car they will experience the same amount of force. We know this from Newton's third law. 
Newton's Third Law states that every action has and equal and opposite reaction. Action reaction pairs are two equal and opposite forces of which include equal sizes and opposite directions. They are represented through vectors. 

For example, if you are holding an apple, the action reaction pair would be: 
-hand pushes apple up; apple pushes hand down. 
-Horse pulls buggy left;Buggy pulls horse right.
-Car hits truck; truck hits car.

A action reaction pair would not be:
-A girl pushing a present up; the earth pulling the present down.
Although they are equal and opposite, they are not a pair. A action reaction pair requires two components, where as this has more than two. 
So another rule of the road is to watch for buggy's! You know, those people on holiday that want nothing less than to be pulled in a carriage by some horses and tour your city! You do not want to crash into them because that would be just bad! 
It looks a bit like this-

 So how does this happen? How is the horse able to pull the buggy if they exert the same amount of force?

 It is important to note that the strength of the pull does not matter. The horse will pull the buggy with the same force the buggy pulls the horse with. We know this from Newton's third law that states that every action has and equal and opposite reaction. The reason the horse is able to pull the buggy is because the horse is pushing the ground harder than the buggy does. The horse and the buggy will move in the direction of the horse. 

Here are the action reaction pairs:

-Horse pulls buggy right; buggy pulls horse left

-Buggy pushes ground forward; the ground pushes the buggy backward

-Horse pushes ground left; ground pushes horse right

6. Lets talk about race cars!

I have to establish the difference between speed and velocity. 

-Velocity requires direction while speed does not require direction.

So this is a simple concept but an important one! On a racetrack you can have a constant speed but not a constant velocity. This is because the race track is circular and constantly changing direction. However, you can still go just as fast on the curves if you wanted to.  

7. Tangential speed is the speed of an object moving along a circular path (radial distance x rotational spin) or (v~rw)

Rotational speed (or angular speed) involves the amount of rotations per unit of time. 

On the race track we see several cars. However take a look at the innermost orange one and the outermost green one. If these cars were to stay side by side the whole race, they will go around the race track the same amount of times, so they have the same rotational speed. However, the outermost green race car will have to have a greater tangential velocity.This is because he located further from the axis of rotation and will have to cover more distance than the car on the inside of the track in the same amount of time. Thus, he will have to go faster and have a higher tangential velocity. 

The size of your wheels can also affect the wheel's rotational velocity. Big wheels= large rotational velocity

small wheels= small rotational velocity.

The bigger the wheels the bigger are, the more mass it has and then the more RI it has. 
The smaller the wheels are, the less mass there is and less RI. 
Tangential velocity is the linear speed of an object moving along a circular path. 
You want a large tangential velocity, which requires wheels moving at a fast pace.

8. Force of Friction

So, acceleration occurs anytime a net force (total force) is on an object. 

Equilibrium occurs when an object is at rest or moving at a constant velocity.  In other words, anytime the net force (total force added together) is at zero. 

Force is a push or pull (measured in Newtons(N). 

Anytime the net force is opposite of the v direction, the object will slow down. 

So when you press the breaks of your car, the Fnet is opposite the v direction and it will bring your car to a stop. 

9. So how does the car stay on the ground and not fly up into the stars and moon? GRAVITY! The gravitational force is proportional to mass (F~m) and inversely proportional to distance (F~1/a). If you're driving on a mountain top, you will experience more gravity because gravitational force is measured from the middle of the planet. 

The Universal Gravitational Law is F=Gm1m2/d². This problem essentially demonstrates the relationship between force and distance².

This way the car will stay on the earth. 

10. Lat but not least, tiny cars! 

Here is a picture of my pal, Henry, and I with our tiny mouse trap car, Thomas! Thomas was a speed demon and demonstrated many aspects of physics. We originally designed him in a fashionable triangle shape with two records and a CD. But after watching some tragic mousetrap car failures, we decided this was a bad idea. After reviewing Newton's second law, we knew that the mass had to be smaller if we really wanted Thomas to accelerate and go fast! We also experimented with other laws, and equations, and all sorts of scientific things. Now, if you want to put your knowledge of cars and physics to the test, make a mouse trap car!  

Wind Turbine

The wind turbine was a project that included several physics components that we learned over the year.

-In order to understand how the wind turbine worked, we needed to know Newton’s Laws. These were found on the website “Newton’s Three Laws of Motion”.

http://csep10.phys.utk.edu/astr161/lect/history/newton3laws.html

1. “Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.” After the wind discontinues, the fan will continue spinning until acted upon by an outside force such as air resistance or friction.

2. “The relationship between an objects mass m, its acceleration a, and the applied force F is F= ma. Acceleration and force are vectors (as indicated by their symbols being displayed in slant bold font); in this law the direction of the force vector is the same as the direction of the acceleration vector”. The mass of the wind turbine is directly proportional to the acceleration. So, the lighter we made the wind turbine, the easier it would be to accelerate.

3. “For every action there is an equal and opposite reaction”

The forces of the magnets towards the coils are equal to the forces of the coils towards the magnets.

Electromagnetic Induction

-Electromagnetic induction occurs when a magnet changes the magnetic field of a current carrying wire. This induces a voltage, which causes a current.

Torque

Torque= force x lever arm

Torque is why something rotates.

In a wind turbine, the turbine will rotate.

Energy Conservation

-In a wind turbine, which is a type of generator (opposite of motor), the energy goes from electrical energy to mechanical energy.

Friction

-Friction could stop the wind turbine from moving because friction is an opposition to motion. If the friction slowed it down, it would create less energy. 

Here are the materials we used:

• Magnets
• A cardboard box
• A flat wooden circle
• Plastic spoons (silver is too heavy- note Newton's second law)
• Wire & current carrying wire
• A plastic cup
• fastener
• LOTS of tape
• LOTS of glue

Magnet Placement 

We put the magnets on the bottom of the flat wooden circle. We stuck them close to the center in order to be close to the coils of wire. This closeness is what made it easier for the voltage to move. 

Coils

Just like our attempt to put the magnets closer to the wires, we also attempted to put the wires closer to the magnet. This occurred for the same reasons

Wind Catching Device

This is where the "LOT of glue" came in. We glued the plastic spoons to the circle (the other side contained the magnets). It hung from the top of the cardboard box and was held in position by the blue cup. The wind would cause the spoons to move and get the whole thing spinning.

This is the overall wind turbine, all put together and lookin' mighty stylish! You can see all the parts with in the cardboard box. 

In the end we ended up generating

• 0.0015 Amps
• 0.0018 Volts

-In order to generate a lightbulb we needed to have generated 0.3 Amps of current. 

 I think from this project, I learned that the voltage can be influenced by the sizing of the wires and magnets. Along with this, and along with the placement, the close the two were to each other, the more energy was created. If the wire is really long, there is more resistance which is inversely proportional to the voltage. 

However, there would be more voltage if the magnets are bigger because of their larger magnetic field. And if the wind turbine spun really fast, a lot of energy was produced. We saw that we had to experiment a few times with the placement of items but after coming to understandings such as the ones stated above, we could notice what worked better where. Thus, we placed the coils and the magnets close together and used a certain amount of coil. Our plan to use the spoons really turned out well. We didn't have to alter many things. It was also hard too because a lot of us missed class due to AP exams, and we needed that time. We didn't really have to experiment that much, we liked the style of it and it was super easy going. My advice to people doing it in the future is to keep an open mind and trust your original plan. Don't be afraid to alter or change plans either. If I could do anything differently, I wouldn't have wasted time trying to uncoil knotted wire. I needed to keep the wire organized in the first place.

Magnetism

In this unit we learned about (the order is weird but just go along with it)

• Magnetism; magnetic poles; Electromagnetism
• Forces on charged particles in an electric field; Motors
• Electromagnetic induction and common applications
• Generators and Energy Production
• Transformers and Energy transfer from Power company to Home

Electromagnetic Induction
-Changes the magnetic field of a loop of wire
-Induces voltage
-Causes current

For example, electromagnetic induction is happening when a traffic light at an intersection is changed when a car approaches. In the concrete there is a coil of wire. When the car rolls over this, the coil's magnetic field is changed. This induces a voltage which causes current. This current signals the light to change.

In a credit card there is a series of magnets. There are coils of wire in the machine. The pattern of magnets change the magnetic field of the wire. This induces a voltage which causes a current. This signals the credit card number thus charging your card.

Transformers
-A transformer is used to increase or decrease the voltage from the wall in order to apply the right amount of voltage needed for an appliance or device.
The primary must have an alternating current (AC) which means the magnetic field of the primary is always changing. Because of this, the magnetic field of the secondary will change as well. It induces a voltage. This causes a current. You find the transformer in an appliance that needs either more or less voltage then the wall supplies. There are two kinds- a step up and a step down. Step ups are used when the voltage given from the wall needs to increase and step downs are used when it needs to decrease to fit the appliance.
Faraday's law states that "the voltage induced is directly proportional to the number of loops".
-It consists of two coils of wire, a primary and a secondary. In a step up the secondary more coils and less in the primary. In step down there are more in coils in the primary than the secondary.
1. A washing machine requires 1600V to work and the wall socket provides 160V. What type of transformer is required?
-Step up
If the primary coil of the transformer has 10 turns, how many will the secondary coil have?

loops primary = Loops secondary

V primary V secondary

10 = x

160 1600

160x = 16000

x=100 coils

If the washing machine requires 100A current, what will the current drawn from the wall socket be?

Power of Primary= Power of Secondary

IV=IV

(160)(I) = (1600) (100)

(160)(I)=160000

I=160000/160

I= 1000 Amps

Right Hand Rule

The right hand rule allows you to know the direction of the force. For example, if a wire in a current is running towards the right of the screen and the magnetic field ran up to the top then the wire will be forced into the screen.




Generators
-Made of coils of wire and magnets
-Goes from mechanical energy to electrical energy
-Electromagnetic Induction
-Spinning magnets
-Induces V in coil
-Causes current (I)

Motors
-Made of coils of wire and magnets
-Goes from electrical energy to mechanical energy
-Rely on the fact that a current carrying wire feels a force in a magnetic field.
-Torque

Magnetic Fields
-The source of all magnetism is moving charges.
-Not all charges have magnetic fields, they have to be moving in order to have one.

• Current Carrying Wires move like this- if the current is moving to the right, the force goes in this direction (black arrows)
  

• Permanent Magnets

The picture on the left shows unmagnetized domains and the right shows one that is magnetized.  A domain is a cluster of electrons that are spinning in the same direction. The one to the right shows that it has north and south poles (moving from south to north). This is magnetized and therefor has a magnetic field.
-Like poles repel and opposite poles attract. Like poles repel because their field lines are moving in different directions and force each other away. Opposites have field lines moving in the same direction. Thus, they attract.
-A compass is a magnet that is free to move

Why do paperclips stick to magnets and each other?
Domains in a paper clip are random. The magnet has a magnetic field. When the magnet is close to the paper clip, the domains of the paper clip align to match the magnetic field of the magnet. The paper clip now has a north and south pole. The magnetic field lines move from south to north on the inside and then move north to south on the outside. And the south pole is attracted to the north. Thus, the paperclip sticks to the magnet.

Why do cosmic rays only enter the Earth's atmosphere in the North and South poles?
Cosmic rays enter there because it will only feel a force and be repelled if they are in a perpendicular position to the magnetic field. So, when the rays are parallel and can enter the atmosphere at the poles, they will enter the Earth's atmosphere. (northern lights)