Unit 5 Blogpost

A. Work and Power

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• Work
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• 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
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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.
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C. Conservation of energy

• Energy is never created nor destroyed
• Energy can only be transformed
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• 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 
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• The work in will be the string you pull and the work out will be the box going up on a tuesday
• Inclined Plane
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• 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