The Top Ten

The Top Ten Places I See Physics

1.) In my room

I experience a Physics moment every time I sit in my desk chair and spin. 

As we learned when you sit in a spinning chair and are pushed you will go faster when you tuck your arms and legs inward. This is because of angular momentum. Angular momentum is your velocity times inertia. Inertia and velocity both depend on the distribution of mass. If the mass is closer to the center of rotation then there will be less inertia which means there would be more more velocity. There would also be less resistance since the arms and legs are closer to the body which means the angular momentum is faster. 

The angular momentum before = angular momentum after

She goes slower while your arms are out because they are further from the axis of rotation which means more resistance and more inertia which means less velocity. 

This is also seen in ice skating. 

2.) In my car. 

When I drive in my car and slam on my breaks I fly forward because of Newton's first law: an object at rest tens to stay at rest unless acted upon by an outside force.

You fly forward when you slam your breaks in the car because you are still moving while your car is stopping since and object in motion tends to stay in motion unless acted upon by an outside force. The seat belt is there in order to stop you from moving. Then when the light turns green and the car starts moving you are pushed back since you were at rest and the car is moving again. There is no force that is acting on you, it is just Newton's First Law. 

3.) In the Library.

When you place a book on the table, the book pushes the table and the table pushed the book right back with an equal force.

This is because of Newton's Third Law which states for every action there is an equal and opposite reaction. So when you place a book on the table in the library the book is actually pushing on the table and the table is pushing right back on the book with the same exact force. You would show this using vectors and saying table pushes earth earth pushes table then table pushes book and book pushes table. 

4.) On the field hockey field.

You learn when playing sports that you must always keep your knees bent, but why is this? 

The reason we bend our knees when playing sports is so that we move our center of gravity closer to your knees and to keep it inside your base of support which is your feet. By spreading your feet out you also widen your base of feet making it harder for you to fall over while playing a sport.

5.) In a garage.

In order to get a heavy object into a car you would generally use a ramp.

The reason you use a machine is because it lowers the amount of force needed by increasing the distance. As the distance increases the force decreases because work in=work out. The ramp is used to make it easier to push a heavy object into a truck because you don't have to apply as much force. If you were to lift the box, the distance would be a lot smaller but that means you would need to apply more force since both ways require the same amount of work. 

6.) On a roller coaster.

The reason we can make it through a roller coaster without stopping is because of the way the hills are designed.

You start off with a really high hill and then it goes to a small hill and then a medium hill. As the passengers KE increases due to the fact the hills go down they will go faster.  The energy you get while going up the roller coaster hill is called potential energy and it turns into kinetic energy as you go down the hill. Since an object in motion tends to stay in motion the roller coaster will continue to move forward in this way until an outside force causes it to stop.

7.) On my roof.

On most buildings there is a lightning rod to protect the home from being hit by lightning.

The lightning rod protects the home by providing an additional path for the lightning to take. It provides a path of least resistance so the lightning will choose this path to reach the path rather than the house or a tree nearby. The ground is positive and the ground is negative so that id why the lightning is attracted to the ground.

8.) Camping.

You want to make sure you having charged batteries before bringing your flashlight on a camping trip or else the light won't work.

In order to make a flashlight work in the first place there must be a complete circuit. The battery must be in contact with the lightbulb. The reason the light becomes dimmer when the battery loses its charge is because there is more resistance which means the light will become weaker. Also if the battery is fully charged and has voltage then the current will be stronger so the light will work but if the voltage is weaker than the current will be weaker.

9.) In the grocery store.

Whenever you are paying with a credit card the machine is able to read your card because of magnetism.

The credit card itself has a magnetic code and the reader has magnetic coils which induce voltage when the card runs through it ]. The reader will copy the card's code and the code will be transferred to the computer where it will then be authorized. 

10.) A toy car.

The motor in a toy car is operated by magnetism.

In general there is a battery with a magnet on top of it, two wires connecting to either sides of batter and connected to the metal loop above the magnet. The magnet will magnetize with the loop above it because the domains will align causing the loop to spin. The force must be perpendicular for this to happen and when it does the loop will move in one direction. The only way to change the direction is by changing the magnetic field. 

Unit 7 reflection

Magnetism, Magnetic poles, Electromagnetism 

What is Magnetism?
Magnetism is the force that is exerted by magnets which attracts other objects with opposite magnetic poles. Another way to put it is that magnetism is the movement between charged objects. When something with one charge moves towards another object with the opposite charge that is magnetism. It can be an electric current. I think the best way to describe magnetism though is the moving charges that cause things to become magnetic.
What are Magnetic poles?
A magnetic pole is one of the two ends of a magnet. It will either be the north pole or the south pole. On the outside of the magnet the electrical current flows from the north to the south pole and the inside of the current flows from south to north. The magnetic field is strongest in these two regions. The electromagnetic interactions cause the opposite ends to attract and the like ends to repel each other. The earths north pole is not actually the north pole and the earths south pole is not actually the south pole. The names were switched because the north end of the compass with points north would be attracted to the south pole of the earth. This is the same with the south pole. When the compass points south it is really the south pole of the magnetic which is attracted to the north pole of the earth. The names are just flipped.

FARADAY'S LAW: induced voltage in a coil is proportional to product of its number of loops the cross sectional area of each loo[ and rate at which magnetic field changes within the loops

What is electromagnetism?

Electromagnetism is a current carrying coil of wire. Its strength is increased by increasing the current. Sometimes the current is increased by adding iron. (pretty much what I already talked about in the previous sections)

Ways the voltage can be induced:

1.) change magnetic field

2.)move magnet / move coil

3.) change current in nearby coil

A few other important terms:

Magnetic force: the force due to the motion of the charged particles

Magnetic fields: the space around the magnet...filings align with magnetic field lines that spread out from one pole to the other

Magnetic domains: a cluster of aligned atoms

Forces on charged particles in electric fields/ Motors

What is a motor?

In order to make a motor you must have the following:

Battery: used to supply voltage and current

Coil of wire: provides a pathway for the current to flow through

Paperclip: the paperclip connects wire to the battery and completes the circuit

Magnet: makes the loop turn because it makes a magnetic field

The force is created because the wire is perpendicular to the magnetic so the upward current puts a force on the charges causing them to move in one direction. They change their direction because of the magnetic field. We had to coil the ends of the wire around the paperclip so it can connect to cause current to flow. There are two forces. One on the bottom and one on the top going in opposite directions causing the spin. 

Electromagnetic induction and common applications 

Electromagnetic induction is an electric force which is caused by the magnetic field around a charged object. The only way electromagnetic induction can occur is if the magnetic field is changing. The magnetic field can be changed by moving the magnets, moving the coils, or changing the current in the nearby coil. This induction can not occur if the magnetic field is staying the same. This is why DC does not work, and AC must be the only way to create induction because the force is alternating. 

One common application where electromagnetic induction is seen is in a generator. The way a generator works is that the mechanical energy is turned into electrical energy. Once the generator has a source of mechanical energy the current will be transformed into electrical energy. 

Transformers and energy transfer from power company

The transformer is used in order to make good use of all of the energy transferred from a power company. They don't want to waste the energy because then they would use money. Sometimes the energy isn't sufficiently used and it is transferred in other ways such as heat. In order to stop this from happening a transformer is used. 

The transfer does this by increasing the voltage which then will lower the current and thus less power is lost and the energy is used sufficiently.

There are two different sides of a transformer the primary and the secondary.

PRIMARY: input

SECONDARY: output 

The equation to prove this is Vp/Tp=Vs/Ts

The voltage of the primary is equal to the voltage of secondary and 

the turns of the primary equals the turns of secondary

Making a Simple Motor

When making our motor the first thing we did was attach the battery onto a a small piece of wood. The next thing we did was create a thick coil of wire and formed it in a circle.
Reason for the battery: to supply voltage and current
Reason for the coil of wire: it provides a pathway for the current to flow. The reason we want the coil to be thick is because the thicker/ the more wire there is, the more current that will flow through causing the motor to have more power.

After making the coil, we attached two paper clips to the north and south pole of the battery. We were able to connect the paper clips by using electrical tape to hold them in place. We wrapped the tape all the way around so that the paper clips were the same height and straight.
Reason for the paperclips: the paperclip connects wire to the battery and completes the circuit. You need a paper clip on both sides in order to complete the circuit.

Then we placed a magnet on top of the wire in order to create the magnetic field.
Reason for the magnet: to make the loop of coil turn because it makes a magnetic field


We then placed the coil on the paper clips, but it was too long. We had to cut the wire and then scrape the entire side of one side but only have of the other. You don't scrape the entire wire of both sides because then the current would want to move in both directions so it will just go side to side and not all the way around. We connected the wire to the paper clip to cause a flow of current.

The coil is moving in one direction because the force is perpendicular creating an upward current putting a force on the charges causing them to move in one direction. They change direction because of the magnetic field.

Why does the motor turn?
The motor is able to turn because of the magnetic field. Since the force of the magnet which is charged by the battery is perpendicular to the motor, it creates a force.

And as seen above the magnet creates a magnetic field. so the charges move in one direction which causes the motor to rotate. It turns because the force is in one direction. If it were in more than one direction the motor will want to pull one way and then pull back and the other way causing it to just go back and forth. That is why we didn't scrape the entire wire so there is still installation on one side causing it to turn in only one direction. 

Reflection

Charges and Polarization including Columb's Law

A charge is when an object is either positive or negative. It is important to remember that like charges will repel each other. And opposite charges will always be attracted to each other. CHarges are transferred through: friction, contact, and induction.

Polarization is the sharing of electrons and protons. If an object is polar it means that the object has both positive and negative charges. 

So why does plastic wrap stick to ceramic and glass bowls but not metal bowls? 

-Because of COULOMBS LAW: the force between any two objects is inversely proportional to distance 

1.) Plastic wrap is charged by friction and when brought near the bowl the bowl polarizes

2.) The positive charges in the bowl move close to negative the plastic wrap and the negative charges between the like repelling charges

3.) The distance between the opposite attractive charges is smaller than the distance between the like repelling charges

F=K(q1q2/d^2)

Since there is a greater distance between the repulsive forces, the force between them will be less than the closer attractive forces thus the plastic wrap sticks to the bowl.

Another good question related to polarization and Coulomb's law is:

Why does our hair stand up after taking a sweater or hat off?

-Because the sweater/ hat will steal all of the protons leaving only electrons left which will then repel each other since they are like charges causing your hair to stick up

Electric Fields

An electric field is the area around a charge that can influence another charge. Positive charges have arrows pointing outward because they will repel any positive charge and electrons have arrows pointing inward because they are attracted to protons. As a charge moves away from the electric field the force becomes weaker and the field shows this by getting further apart. 

OHM'S LAW

States that voltage is directly proportional to current times resistance. 

And in order to figure out the force of an electric field you say the electric field=the amount of force per coulomb. 

What is Electric Shielding?

-if you are inside a metal container the forces counter act because they are pulling from every direction so that no force is felt

SO then why are electric devices put in metal containers?

-so we keep the positive charges where they are because you don't want any negative charges near them 

Electric Potential/ Electric potential Difference/ Ohm's Law and Capacitors

OHM'S LAW

States that voltage is directly proportional to current times resistance. 

And in order to figure out the force of an electric field you say the electric field=the amount of force per coulomb. 

-So when there is more current the resistance is less but when there is more resistance the current will be less. 

-The Potential difference is when the circuit is completed. There must be two unlike charges which are different that must be attracted to each other to form a circuit. Without potential difference there would be no way for the current to travel through the circuit because there would be no circuit. Voltage is also potential difference per charge

PE/charge

V= change in PE per charge

measured in Volts 

A conductor is used in order to create more resistance so that less current will flow through.

Types of Current, Source of Electrons, Power

Current is the flow of charges through a circuit. Current is measured in amperes and in order to find current you use Ohm's law which is V=IR.

There are two types of current which are AC and DC

AC stands for alternating current which is when the flow of electrons switches from forward to backward.

DC stands for direct current where the flow of electrons is direct and only flows in one direction. 

The electrons which flow through the current are not supplied through power but they are already there. Power is the amount of voltage in the current.

Power=VI

Power companies don't sell power like their name implies but they sell energy.This energy is used in current. They do not sell electrons because electrons are already there and they do not sell power because power is what is generated.

In order for there to be a current though there must be a potential difference and the circuit must be completed.

**Flashlights**

Why do flashlights get dimmer as the batter becomes weaker?

-Because as the batter becomes weaker it means that the current is less because the voltage is lowered. With let current means there must be more resistance so the light will become weaker.

Why do bulbs often blow when they are first turned on?

-Because when bulbs are first turned on the filament is generally really cold so the hot current flowing through will be so hot there is little resistance causing the bulb to go out. But as the heat in the filament increases the resistance will increase so that the bulb will not blow out.

Parallel and Series Circuits

A Series circuit is a circuit which looks likes: 

Where the current travels straight through both of the lightbulbs. The resistance in a series circuit goes up as more appliances are added, which then causes the current to go down as more appliances are added, then causing the brightness to go down as more appliances are added. If a lightbulb were to stop working in a series circuit then the will all go out. This is because since they all have the same current running through them they will all go out if one bulb were to be removed. Series are not used in homes because of this fact.

A Parallel circuit looks like: 

The current is divided into two different paths in a Parallel circuit. The resistance will go down as more appliances are added causing the current to increase as more are added to the circuit. The brightness will stay the same though because voltage is the exact same for each branch in the circuit. If one of the bulbs were to go out though they are not all effected because they each have their own branch with the same amount of voltage. This is why they are used in most households. 

How is fuse wired and how does it work?

-They are used if the current gets too high it could overheat and the wiring could cause a fire so fuses/circuit breakers are used to protect. At a certain current level they shut off all of the power from the circuit. In order to do this they must be wired in series with the rest of the circuit.  fuse blows by melting the wire inside. Fuses protect your house because when the circuit overheats the fuse wire will melt so that the current will not pass through the circuit.

This unit has been the hardest unit so far for me. I have really struggled with my understanding of almost all of the different topics. It took me a while to grasp current in particular. Once I did though and I went in to conference period a few days I felt a lot better. I think that my effort has been pretty solid but not as good as it could be. I think that what I could do in the future is take better notes, because for some reason my notes for this section were a little disorganized. I am expecting to do well on this test but again this unit was particularly hard for me. 

Ohm's Law

This Video gives a simplified run-through of Ohm's Law which is easy to follow and not too advanced. He talks about voltage, current, and resistance and exactly what they are before he goes into talking about Ohm's law. I found this really helpful to think about each thing individually before looking at it as a whole. I chose to focus on Ohm's law because I was a little unclear of why and when you would use it. I was reminded of all of the symbols and also saw an example of using the equation which I found very useful.

What is Voltage?

This video gave a good simplified explanation of what voltage is. It gave the definition: voltage is the measure of electric energy per unit of charge. It also reminded me of the units of measure as well as the symbols. The symbol for voltage is v and it is measured in J. This video will be good to go back to when I need a simple reminder of what voltage is and how it can be found and why you would need to use voltage. The video helped me to see how simple voltage really is and how we see it everywhere such as batteries.

Mousetrap Car

        Speed of car: 6.57s
        Place in F block: 5th
     

This is a model of our car that we used. 

The wheels: 2 CD's in the back with balloons wrapped around the edges and a toy car wheel in the front with two bottle caps glued on either side

The sides: two light weight pieces of wood attached to the mouse trap

The axel: in the back we used a medal small axel and then drilled it through a piece of glue to make it thicker and in the front we used the same metal axel but without 

The lever arm: we used a pencil as our lever arm and fishing line as our string

          The mousetrap car can be related to all three of Newton's laws. Newton's first law states that and object in motion tends to stay in motion unless acted upon by and outside force and an object at rest tends to stay at rest unless acted upon by an outside force. This is related to the car, because once the car is moving the only thing that will stop it from moving is an outside force. This outside force could be a physical object or it could be friction. Our mousetrap car stopped because there was a lot of friction. The mousetrap caused it to move but once the friction caught up with the car it was brought to a stop. The car will not start to move unless acted upon by and outside force, in this case the mousetrap itself is what causes the car to move forward. Newton's second law states that acceleration is proportional to force and inversely proportional to mass. This means that the more force applied the car the more the car will accelerate and the smaller the amount of mass the faster the car will go. We tried to use the lightest weight wood and wheels because we knew that less mass meant it would  travel faster. The amount of force applied is also important to make the car move faster. We used a lever which created more force and more acceleration. Newton's third law states that for every action there is an equal and opposite reaction. This is seen in the care in several different ways. One example is that when the car pushes down on the floor while moving the floor pushes back on the car. Another example is when the mousetrap pulls the string that is wrapped around the axel the axel is pulling the string. It is important to remember that these forces are equal and opposite.

       There are two types of friction that are present. The first type is static friction which is only seen when the car is at rest. Static friction is what what makes it difficult for the car to begin to move. The other type of friction is kinetic friction which is see when the car is in motion. Kinetic friction slows the car down when it is in motion. One problem we had with friction was with the wheels. We added balloons to the wheels in order to make it smoother and thus decreasing the friction. We also encountered friction when designing our axels. We chose to use a thicker axel to attach the string to because in this case we used friction to our advantage. This is because it was applied closer to rotation thus making the torque smaller requiring less force. One mistake we made was that we glued two bottle caps to the front wheel which created more friction. It was good to have friction on the back wheels so that they wouldn't slide but the added friction to the front wheels made it harder for the car to accelerate. 

        When choosing our wheels we wanted something lightweight because we know that the smaller the mass the greater the acceleration because of Newton's third law. We also decided to use larger wheels in the back (CD's) because they were the wheels that controlled the whole car. We chose to have only one wheel in the front, because it would mean less mass and a smaller rotational inertia. A smaller rotational inertia means that the wheel will rotate more.The wheel in the front was only there so the car would move, it did not control the car. One mistake we made was that we glued two bottle caps to either side of the front wheel which added mass and it created more friction. Our car still made it 5m but it would have been a lot faster if the front wheel had a lower rotational inertia. The way to lower this rotational inertia is by making the wheel smaller.
         Before the mouse trap car was moving it had the highest amount of potential energy. Potential energy is the amount of energy an object has right before it begins to start moving. Once the car was in motion it's potential energy lowered while the kinetic energy became greater. Kinetic energy is the amount of energy an object had while in motion.When the car was at it's highest velocity it had the most amount of kinetic energy. Once the car started to slow down again though it's kinetic energy lowered and it gained potential energy in return.
       For our lever arm we used a normal pencil. It was shorter than the length of the car and without it our car would not have traveled 5m. For our first test trial we tried attaching the string just straight to the mousetrap without and sort of lever arm and it only made it about 3m. By using the lever arm we increased the torque and by increasing the torque we increased the rotation. There are three ways of increasing the torque. One way is by adding more force. The second way is by increasing the lever arm. And the third way is by doing both of these things. We just increased the lever arm which increased the torque and required less force. 

        Rotational inertia was seen in our wheels. The larger the wheels the more rotational inertia. The more rotational inertia the wheels have the harder it is for them to rotate. We had larger wheels in the back that had more rotational inertia than the front wheel. This causes them to be the wheels that drive and control the car though. Like the train wheels the larger wheels control the car. We chose a small wheel in front because it was just there to keep the car moving so we wanted it to have a really low rotational inertia. One mistake we made though was gluing two bottle caps to either side because this increased the rotational inertia making it harder for the wheel to rotate. The wheels have different rotational velocities because one wheel is smaller than the other wheels so it is rotating more than the back to wheels. All of the wheels have the same tangential velocity though because all three wheels are covering the same amount of distance in the same amount of time.
        Work is the measure of how much force is done in a certain amount of distance. We are unable to calculate the amount of work the spring does on the car because we don't know the amount of force the spring is putting on the car. We also don't know the potential energy and the kinetic energy in the spring that the car used. If we knew this information it could help us calculate the work because work is equal to the change in kinetic energy which is equal to the change in potential energy. We are unable to find the kinetic and potential energies because we do not know the mass of the spring in relation to the car. KE=1/2mv^2 we know the velocity but we cannot find the KE without knowing the mass. Same thing goes for PE. PE=mgh we know the gravity but we do not know the m and the h so we cannot find the potential energy. The reason that we cannot find the force the spring uses on the car is because we do not know the mass and we would have to calculate the acceleration since force=(mass)(acceleration).

Reflection

We followed our original design pretty well. We kept everything except once we did our first trial run without a lever arm we realized that we had to have a lever arm if we wanted our car to travel the 5m. One thing that we added that  made it worse was we glued two bottle caps to the front wheel. This created more rotational inertia which made it harder for the wheel to rotate, slowing down the car. We thought that this was necessary to make the car stay in place but it was not necessary. If we were to do this project again I think I would make the car have a smaller mass. This would mean not using wood but just try to connect the mouse trap straight to the axels because the smaller the mass the faster the car would go. I would keep our wheel set up though because I think that the small wheel in front (without the bottle caps glued to it) and the two CD's in the back worked well. Overall I was happy with our car though because it made it the 5m and it was overall successful although it was not very fast.