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.

Unit 5 Reflection

Work and Power

Work is the amount of force that is applied for a certain distance, and it is measured in Joules.
         WORK=FORCE X DISTANCE

If you were to lift up a box that weighs 20N 2m high, how much work would you do? Using the equation work=fXd you would get 400J.

You can only do work if you are lifting an object. You are not doing work if you were to just carry a box for a certain distance. You are not doing work, because the force and distance are parallel. The only way you can do work is if the force and distance are perpendicular (carrying a box).

Another example of someone doing work is running up a set of stairs.

The man in this picture has a force of 600N and he is moving up a set of stairs with a distance of 10m, how much work is he doing? 

      He would be doing 6000J of work. It is important to remember that the distance is not distance of

      the stair themselves but it is the height of the stairs. 

Power is the amount of work that is done in a certain amount of time, and it is measured in watts. Another way to word it is how quickly work is done. (power=work/time). 

Here's an example problem:
If you do 6000J of work in 60 seconds, how much power was produced?
    Power=work/time
    Power=6000/60
    600 watts

Work and Kinetic Energy

Work and energy are connected because work is the change in kinetic energy. This means that the work will always be equal to the kinetic energy. Energy is the ability to do work. Kinetic energy is the change of movement. It is related to the velocity because the equation is KE=1/2 mv^2. In order to fin the change of kinetic energy you must know the finial KE and subtract the initial KE.

Here's an example:

If a car is moving 20 m/s and requires 10m to stop. How many meters will it take to stop if the speed of the car is 40 m/s?

First you must realize that work=forceXdistance then remember work= the change in KE.
KE=1/2 mv^2
since you are going twice the speed you plug two in for v
which equals 4
this means you are going 4 times the speed and since work=KE you doing 4 times the work and going 4 times the distance.




Another question that is related to both work and KE is: why do airbags keep us safe?

Conservation of Energy

The conservation of energy means that the change in potential energy is equal to the change in kinetic energy. Potential energy is the energy stored within an object. It means that the energy has the potential to do work. In order to find the potential energy you must know the mass, gravity, and the height. The equation looks like this PE=mgh.
Kinetic energy is the energy of movement. It depends on the motion of an object. In order to find the kinetic energy you must know the mass and the velocity. The equation looks like this Ke=1/2mv^2.
The energy is conserved because when you lose one you gain the other.

Here is an example:

The ball doesn't hit the womens face because it was dropped from rest. This means it will not get any higher than it was dropped from. When she drops it the ball has the most amount of potential energy and the least amount of kinetic energy. The ball while in motion loses it's potential energy and when it is straight it has the highest amount of kinetic energy and the lowest amount of potential energy. 

Energy is always released in some shape or form. A car for example does not use all of its energy to accelerate forward. The energy is also released in ways like heat, light, vibration, and sound. 

In order to find out how efficient an object is you would calculate work out over work in.

Machines

Machines are used when you are trying to move a heavy object. They are useful because they make the objects easier to move. Machines make it easier because they require less force. They sacrifice force for more distance. If you were to lift the same exact heavy object without using a ramp you would do the exact same amount of work since work in = work out. The difference is that you use much more force when lifting the object over a short distance. With the machine you use more distance and less force.

Machines are not always used to lift objects. Another example are metal cutting shears. These shears have very long hands with much shorter blades.

These are able to cut through metal because the handles are long. This means that less force is required to use them. 

Here's an example question: If two people are in charge of putting some boxes into a bus that is 1m tall and they both grab 200N boxes but one person uses a ramp while the other lifts the boxes, who does more work?

They do the exact same amount of work because, one person uses more force while the other person uses more distance.
work= F X d
vs.
work= F X d

This unit in physics has been challenging for me. I felt rushed when learning these concepts and I never fully understood every aspect. I am comftorable  with work and power but once it gets into kinetic energy and potential energy I get lost. There are still 2 big questions that I am struggling with but I think with more time (when I study) I will be able to go over them a few times and be ready for the test. This unit though I would say I have caught up with.  I have done all of the homework assignments and watched all of the videos. I just feel like this is one of the hardest units and I still feel a little behind even though I have done all the work to stay caught up. I feel like I have put a lot of effort in though. Next unit I will continue to study for each quiz and begin studying for the tests further in advance. I think that now that I have prepared in advance for this test I should be ready!




 

Simple Machines

A simple machine is something that is used when you are unable to apply enough force in order to lift an object. A machine allows you to lift heavy objects. Machines help you to lift large objects because they increase the distance which means less force is required. When you do not use a machine you are required to use much more force because the distance is extremely small.(F)(d)=(f)(D). This means that the work will be the same as well. work in=work out. Bill Nye is really good at explaining the different ways machines are used and how they work. He explains where the work in is and the work out. Bill Nye is awesome and I think that this video is really clear.

Work and Power

This video does a really good at explaining work in force in a relatable way. Work is the amount of force applied for a certain amount of distance. If you were pushing a box with a force of 20N for 2m then the work applied would be 40J. Work= force X distance. Work is not applied if the force is not parallel though. For example if a waiter is carrying a tray there is no work being one on the tray. He explains how work is seen in a grandfather clock. When the cylinders inside the clock move in order to power the clock they have to be moved with a force that is equal to their weight. Power is how quickly work is done. In order for there to be power there must be work that is applied. Power is measured in something called watts. This video provides step by step explanation of how to find power and weight using a grandfather clock as the example. I really liked this video because it simplifies the whole concept and gives relatable and common examples.