Unit Seis

A. Charges and Polarization including Coulomb's law

• Types of charges
• Positive
• Negative
• Opposite charges attract

• Positive charges will be drawn to negative charges and will be repelled by positive charges and vice versa

•  An object can be
• Positively/Negatively Charged
• This mean the electrons or protons outnumbers the other causing the object to be overall charged
• Neutral
• Polar
• All protons go to one side and electrons go to the other giving it charged sides but remaining with an overall neutral charge
• 
  
• Non-Polar
• Protons and electrons are evenly distributed
• Three ways an object can become charged
• Induction
• Lightning
• Contact
• Static Electricity
• Contact
• Balloon on Wall
• Coulomb's Law is used to measure the attraction between two charges
• 
• In this formula distance has the biggest impact because it is squared

B. Electric Fields

• An electric field is the area around a charge that can influence another charge
• How close two things must be to attract or repel one another
• Arrows
• An arrow of an electric field shows the direction in which a PROTON would go in that electric field
• 
• In the picture above, the proton would be repelled from the proton and attracted to the electron
• Electric Shielding
• A force within a sphere that will feel no force
• Metal keeps electricity
• Examples
• Seran Wrap on a Bowl
• Electronics encased in metal
• 

C. Electric Potential/Electric Potential difference, Capacitors

• Electric Potential measure how much power something can put out
• Only matters if there is a difference in electric potential
• Birds on the electric lines
• The lines are far enough apart so that the birds never touch another wire and get shocked
• This is because the lines have difference electric potential and the bird would complete a circuit between the two
• A difference in electric potential is voltage
• Capacitors
• Two sides
• Positive
• Negative
• The sides are attracted
• They are briefly connected and emit energy
• Example
• Flash on a camera
• When they are connected light is emitted and the flash then goes off and shines a light
• D. Ohm’s law and electric potential difference
• I= Current
• Amps
• V= Voltage
• Volts
• R= Resistance
• Ohms
• Current is directly proportional to voltage applied to a device
• Current and resistance are inversely proportional\
• Resistance
• To increase resistance, increase thickness of the wire
• To increase resistance decrease temperature
• Example questions:
• A circuit has a current of 40 amps and a voltage of 20. What is the Resistance?
• 2 ohms
• A circuit has a 120V and 60 ohms of resistance. What is the current?
• 2 amps
• The only reason why a circuit has voltage is because there is a diffence in two volts. Each side has a different amount of

E. Types of Current, source of electrons, Power

• Types of Current
• Alternating
• The electrons within this circuit move back and forth
• Start by going forward then reverse directions
• Direct
• The electrons within this circuit move in the same direction at all times and go around the circuit
• 
• Where do electrons come from?
• When we get power from the power company, a common misconception is the idea that we pay for the electrons. This is not true. We pay for current which causes the electrons to move. The electrons are already in the wires and running through our homes, but we must have current for them to move.
• Power= Current*Voltage
• Measured in watts
• Also defined as work over time
• 
• Rate at which work is done over a certain amount of time
• J/s

F. Parallel and Series Circuits

• Types of circuits
• Series
• One circuit total
• All devices must be connected and on for all to work
• This is because the devices complete the circuit
• As devices are added the current goes down because they are each taking away from he same amount of power
• Fuses and circuit breakers are wired in series so they cant cut the entire system off when the current is too high
• Parallel
• Independent circuits within the entire system
• Devices can be disconnected and others will still work
• Most houses are wired in parallel 
• Current goes up and resistance goes down as more devices are added to the circuit
• Fuses and Circuits prevent fires because parallel circuits can get hot as more devices are added

Physics Mousetrap Car

Newtons laws were very applicable to the cars performance. The first law told us that the car wouldn't stop unless there was an external force acted upon it. The only external force that would act on our car would be the force of friction. This told us that we wanted to have  surface or wheels that would have as little friction as possible. Friction was our enemy within this project. The second law told us that we want to make the object as small as we could because we wanted the quickest acceleration. To get a high acceleration you want to maximize force and decrease mass. Our force was constant so the smaller the car the better. The third law told us that each reaction had an equal and opposite. This means that as the car moves friction will cause it to slow down. Also as the string pulls the axle to axle pulls the string equally but since the car has a small mass the force is able to cause it to move. This means the force of the mousetrap is greater than the force of friction. The part of the car that we wanted to have friction was the part where the axle touched the wheels. This was helpful because if there isn't friction on the axle will turn without the wheels, and we want to maximize their rotations. On the other hand friction on the wheels was bad because the more friction the ground would push the car back. You also do not want friction on your axle to string. This is why we added a balloon on our axle to reduce friction between it and the string. Our wheels began too small; they had little rotational inertia but couldn't gain very much tangential velocity as disks could. This is why we switched to get bigger disks. The disks were not too hard to get a torque but they were also able to get a great tangential velocity. The car's only force was the force of friction as it moved and the force of the trap. The trap is what made the car go forward and it had the same amount of energy as it went. But as the car went forward friction would slow it down until it completely stopped the car. The potential energy is stored in the spring and then when you let it go it is converted into kinetic energy. We can't calculate the work of the spring because the spring's direction is not parallel to the direction which the car is moving.

Reflection-
My final design changed a great deal. For one, the wheels had to adjust to become disks because our original disks were too small. Also we added a balloon on the axle to increase the friction between the string and axle. We also added tape to the wheels to decrease friction between the ground and wheels. We also used yarn rather than string because it was much stronger and sturdier. One of our problems was winding the yarn because sometimes the wheel with the axle was our front wheel and we wanted it to be our back wheel. We also had to use several pieces of yarn because they kept getting tangled causing the yarn to stop half way through the run. If I could do the project again, I would have started earlier. I would've finished it sooner so I wouldn't have had to adjust after it was too late. If I were doing another building project, I would work in a group of three because the work is then divided into smaller parts. Also I'd add someone who has past experience in the subject because neither of us knew what we were doing.

Unit 5 Blogpost

A. Work and Power

• 
  
• Work
• 
  
• In order for work to be done, the force must be parallel  to the distance moved. 
• Work is a force that is applied to an object moves that object
• Work is defined as distance x force
• Force and distance have an equal affect on work
• Distance and work, and force and work are directly proportional

• Take this waiter for example
• In the picture above, the waiter is not doing work on the tray
• This is because the force down (the weight of the tray) and the distance that the tray moves is horizontal 
• Work is measured in Joules 
• Joules is also J
• Work is unaffected by time
• Regardless of how fast something is done, it will require the same amount of work
• Power
• Power is the rate in which work is done
• Power is defined as work/time
• Power and work are directly proportional
• Power and time are inversely proportional 
• Power is measured in watts
• 

B.Work and Kinetic Energy Relationship

• Work
• Work is distance x force
• Work is measured in J
• Work is a force that is applied to an object to move the object
• Kinetic Energy 
• Kinetic comes from Greek
• Kinema means moving such as cinema/movies
• Energy comes from the works "en" which means in and "ergon" which means work
• Energy is the ability to do work
• Movement
• Work and  the change in kinetic energy are equal
• If there is 40000J of work being done there is a change of 40000J in kinetic energy
• Work and kinetic energy are directly proportional
• Airbag question: Why do airbags keep us safe?
• Airbags keep us safe because they decrease the force we hit the wheel with. Regardless of how you stop your work will be the same because you will go from moving to not moving and change in kinetic energy is equal to work. Knowing this, we know that the work will not change. If the distance goes up, which is what the airbags do, the amount of force will therefore have to go down to maintain the work. The airbag increase the time and distance in which you slow down, so thereby decreases the force you hit with so you get hurt less.
• 

C. Conservation of energy

• Energy is never created nor destroyed
• Energy can only be transformed
• 
• As the kinetic energy goes up the potential energy goes down
• As the potential energy goes up the kinetic energy goes down
• Potential energy is the energy of position
• The higher up you are the more potential energy you will have
• It is how much energy you can acquire by going down
• Kinetic energy is the energy of movement
• The change in kinetic energy will be equal to the change in potential energy
• We know this because the potential energy at the top will be equal to the kinetic energy at the bottom

D. Machines

• A machine is something that makes it easier to do something
• Not exactly
• A machine makes it seem easier to do something like lift a box 
• No matter how you lift something, the work required will be the same amount
• A machine decrease the force required to lift it, but it also decreases the force
• This is why it feels easier
• Types of machines
• Pulleys 
• 
• The work in will be the string you pull and the work out will be the box going up on a tuesday
• Inclined Plane
• 
• The work in will be you pushing it on the ramp and the work out will be the vertical height of the ramp
• Most machines are not efficient
• Machines will get less work out than the work in
• For example, a car only uses 30 percent of the gas to move the car
• This is because energy is lost in friction as heat and energy will remain the same
• To calculate efficiency you put work in/work out and multiply it by 100 percent

Blogpost 4

A. Rotational and Tangential Velocity

• Factors of Circular motion
• Tangential motion
• Linear speed of something moving in a circle
• How fast an object with a circular path is moving
• Usually measured in m/s or km/h
• Rotational Speed

•  Also called angular speed
• Evaluates the number of full revolutions an object does over a period of time
• On a line from the center of a circle to a point on the outside, all objects on the line will have the same rotational speed
• If you begin at the center of a table and crawl outwards as it spins the rotational speed will remain the same
• Tangential speed is directly proportional to rotational speed at any fixed distance from the axis of rotation
• Examples
• 2 kids are on a merry go round. One is on the outside and one is on the inside. The one on the outside will have a greater tangential velocity but they both will have the same rotational velocity. This is because the make the same rotations in a period of time but the one on the outside will cover a much greater distance.
• 2 gears. One large and one small. They will both move one tick at a time, but since one tick is the same distance they will move at the same speed. On the other hand the smaller one will have a greater rotational velocity because it may have 10 ticks and the other has 30. So they move at the same tangential speed but the small one will make 3 full revolutions as the big one makes one.

B. Rotational Inertia

• The property of an object to resist changes in its rotational state of motion
• Greater rotational inertia makes it much harder for it to fall or rotate over
• Something rotating will continue rotation while something not rotating will remain at rest
• Dependent on mass
• More specifically mass distribution
• The further the mass is from the axis of rotation the greater the rotational inertia will be making it harder for the object to rotate
• Tightrope walkers use long poles to take advantage of this
• The pole has a great rotational inertia and the longer the pole the harder it would be for them to rotate
• An object with a high rotational inertia is harder to get sped up, but once they begin rotating they have a tendency to continue rotating
• A long baseball bat is much harder to swing but it will continue to rotate once it begins to rotate
• A ring will lose to a solid marble regardless of their mass because a hoop has a great rotational inertia
• It is much harder to get spinning

C. Conservation of Angular Momentum

• If no external net torque acts on a rotating system, the angular momentum of that system remains constant
• With the weights far away from the axis of rotation he moves at a slow speed but when he pulls the weights in close to him, he speeds up
• Though he goes much faster the angular momentum remains the same
• If he were to put the weights back out, he'd slow down again
• Pulling the weights in makes him easier to spin because 
• Similarly, a diver in the air
• While flipping divers will sometimes "tuck" 
• Brings legs in towards chest and curls up with a "cannonball"
• Allows you to rotate much faster because you decrease your rotational inertia
• As he goes up he will go slow
• As he tucks, his rotational speed will increase
• As he leaves the tuck, his rotational speed will go back down
• Throughout the entire flip his angular momentum remained the same

D. Torque

• Rotational counterpart of force
• Torque causes a rotation or twist of an object
• Defined as torque= lever arm x force
• Lever arm is the part of the system that provides leverage
• The shortest distance between the applied force
• Torque is directly proportional to both lever arm and force
• The ratio of effect lever arm an force have on torque is 1:1
• They have equal effects on torque
• 2 children on a seesaw

• One is twice the force as the other
• The smaller one will need a bigger lever arm so must be further from the center of the seesaw

E. Center of Mass/Gravity

• Center of Mass
• CM
• The average position of all the mass that makes up an object
• A symmetrical object will have its center of mass directly in the center
• An irregular object will have its center of mass closer to the bigger side
• The center of mass doesn't have to touch the object at all
• Center of Gravity
• CG
• Same as CM since mass and weight are proportional
• The center of mass cannot go beyond the base of support or the object will rotate/fall over
• This is why athletes are told to crouch and bend their knees.
• Much harder for them to fall over 
• Much harder for them to get knocked over

F. Centripetal/Centrifugal Force

• Centripertal
• Center seeking
• Pulls inward toward the center of a circle
• Tin can whirling on a string, you must keep pulling the string
• String omits the centripetal force
• Centripetal force depends on the mass of the object
• Also depends on tangential speed and radius of the circle
• Centrifugal Force
• Center fleeing
• Not real 
• NEVER THE ANSWER
• NOT WHAT CAUSES YOU TO KEEP GOING STRAIGHT IN A TURNING CAR
• Turning car is by properties of inertia
• Nothing made you stop, so you continued going straight

Meter Stick

Step 1:
A. Gives an example of a meter stick with a torque
Shows that the position of the fulcrum determines whether it will be balanced

B. Shows the meter stick being balanced on the table also showing that if they are balanced there are two equal torques

The center of gravity was very close to the 50cm mark  and the lever arms were then equal at about 50cm

C.We then added the weight to one side of the meter stick. This changed center of gravity therefore we had to change the location of the fulcrum to keep them balanced.

When balancing each side, lever arm and force were inversely proportional. The force on one side went up therefore its lever arm had to decrease to keep both torques equal to each other. On the other side the lever arm went up to balance.

Step 2:

1. Balance the meter stick
2. Measure each lever arm
3. Convert mass of the additional weight that was clamped on to weight
4. Use three solved variables in the formula for torque and counter torque to solve for the final (force/weight of meter stick)
5. Convert force of meter stick to mass

Step 3:

Torque= Counter-Clockwise Torque

Lever Arm(A) x Force(A)= Lever Arm(B) x Force(B)

23 x .98= 27 x Force(B)

22.54=27 x Force(B)

Force(B) = 8.348

Mass= 0.0851kg

Mass= 8.51g

The method that I developed worked because all I had to was make calculations and plug them into a formula with one variable. This is what the torque formula allowed me to do. We had the resources to find both lever arms and the mass of the weight added to the side was given. Unless given more information this was the only way to do the problem. When the weight was added and we were told that we had to keep them balanced, you immediately know that the lever arm would have to be increased on the other side so they could have the same torque. 

2 Resource Posts

I found this resource helpful because of the examples he provides throughout the video. He begins with a simple definition of center of mass and goes on to give an example that everyone understands and then goes on to explain other examples of where the center of mass on different objects would be. This video also helped me fully understand an object that has a center of mass that doesn't touch the object. The boomerang will have a center of mass and axis of rotation in the center, and will not touch the boomerang. 

http://education-portal.com/academy/lesson/what-is-torque-definition-equation-calculation.html

This resource was helpful because of its use of diagrams. Each diagram was an explanation of torque and they allowed a person to visualize the ideas literally or conceptually. Regardless of the type of learner you are, you could easily learn torque. 

Unit 3

A. Newton’s 3rd Law and  Action/Reaction Pairs

• Newton's third law states that every action has an equal and opposite reaction

• For example, when you walk, you push the ground back and the ground pushes you forward
• The difference is that the ground has a much greater mass so its acceleration is much less
• Another example is if you push someone in a chair 
• You push the chair and the chair pushes back on you
• The reason you don't move is because you push the ground forward and it pushes you backwards
• This is similar to the tug of war/horse and buggy
• Even if nothing is in motion forces are still in action
• If a book sits on a table the book is pushing the table down and the table is pushing the apple up
• The book is always being pulled down by the Earth and the apple pulls the Earth up

B. Tug of war/horse and buggy

• Many people are under the impression that to win a tug of war battle you must pull the hardest
• This is false
• We know that from Newton's Third Law every interaction there is an equal and opposite reaction
• This means that pulling the rope harder just means the other team pulls just as hard
• The truth is that winning is not based on how hard you pull
• Rather it is based on how hard you push the ground

• The person who pushes the ground the hardest will have the ground push them back the hardest, therefore the winner is whoever pushes the ground the hardest

C. Forces in perpendicular directions

• This is best described by a box sliding down a ramp
• 
• The weight of the box is caused by gravity and will always be in the downward direction
• The box pushes up while the ramp pushes down
• When drawn the vectors will end up in the diagonal direction causing the box to accelerate down the ramp
• The steeper the box, the greater the acceleration the box will have
• This can also be seen in someone canoeing across a current going downstream
• If there is a velocity going down stream and a velocity across the velocity will end up being in the diaganol direction and the person will not canoe straight across

D. Gravity and Tides

• The force of gravity is increased as the mass of the object increases


• The more mass an object has, the more it is attracted to other object
• The force of gravity is defined by the formula: 
• As mass goes up so does the force
• They are directly proportional 
• As distance goes up, the force goes down
• They are inversely proportional
• This is why the moon has a larger impact on the tides than the sun does
• Though the sun's mass is much greater than that of the moon's,the moon is much closer
• When mass goes up by the same factor that distance does, distance  has the greater impact
• If mass goes up by a factor of 2, the force doubles
• If distance goes up by a factor of two. the force goes down to 1/4 of the original force
• The reason why distance has a greater affect is because it is squared
• The tides of the Earth are most affected by the moon
• The force of the moon on one side, and the much less force it has on the other side of the Earth is what causes what is called the tidal bulge
• The tidal bulge is caused by the moon pulling on side very hard, and very weak on the other side, because they have a greater distance
• The moon pulls one side hard, the Earth comes over some and then the oceans are spread thin causing the North and South side to have lower 
• When the moon is on the East side of the Earth, the oceans on the East and West side will be in high tide, and the North and South side will be in low tide

E. Momentum – and Impulse momentum relationship

• Momentum is a way to describe an object in motion and with relation to the object's mass
• If two objects are in motion with the same velocity but one with a higher mass, the one with the higher mass will have the higher momentum
• Momentum is also p
• p=mv
• When an object's momentum changes over a period of time, it is called an impulse
• Impulse is also equivalent to the change in momentum
• Impulse is J\
• J is also to be calculated 
• Impulse is what determines how you hit the airbags 
• Regardless of how you hit the airbags you will go from moving to not moving
• The airbags increase the time but impulse will not change
• The airbags therefore decrease the F
• The impulse of you hitting the airbags versus hitting the dashboard are the same because the change in momentum is the same:moving to at rest

F. Conservation of Momentum (Including the lab)

Within a system we know that momentum is conserved

For example, if a 5kg cart is moving at 6m/s and it hits a 1kg cart and stops, it has to have the same momentum as the other cart

• It will be moving at 30m/s
• This can also be solved by using M(a)V(a)+ M(b)V(b)= M(a)V(a)+M(b)V(b)
• 5(6)+1(0)=5(0)+1(x)
• 30+0=0+x
• 30=x
• If the objects stick together then you must use another formula such as M(a)V(a)+M(b)V(b)=M(a+b)V(ab)
• The ab at the end are not to be multiplied but is to show that the two objects are now one and stick together
• If the objects in the previous stuck together rather than the first one stopping it would be 5(6)+1(0)=6x
• 30+0=6x
• 30=6x
• x=5m/s