Potential Energy Kinetic Energy Transformations Energy Conservation By

Potential Energy & Kinetic Energy Transformations; Energy Conservation By Nickey Walker

Mechanical Energy Potential Energy: stored energy; energy of position. (Springs, bow strings, rubber bands, chemical energy from food/fuels etc. ) Kinetic Energy: energy of motion.

Kinetic Energy: energy of motion KE = ½ 2 mv (S. I. Unit : Joules (J)

Describe the energy, as the cart rolls down the ramp. Potential energy transfers to kinetic energy.

http: //www. physicsclassroom. com/mmedia/energy/se. cfm

KE=1 2/3 J PE= 3 1/3 J KE=3 4/5 J PE=1 1/5 J How much total energy will the object have?

How much work was done if you had energy bar graphs with these numbers? KE = 3 J PE = 6 J ΣE (TME) = 9 J KE = 5 J PE = 3 J ΣE (TME) = 8 J W = 9 J – 8 J = 1 J

Work = Kinetic Energy Start with : F=ma Multiply each side of the equation by d Fd=mad 2 Fd=mad (By substitution, d = ½ at ) 2 Fd = ma ½ at 2 2 Fd = ½ma t (By substitution, v=at) Fd = ½m(a 2 t 2) Fd = ½ mv 2

http: //phet. colorado. edu/sims/html/energy-skate-park-basics/latest/energyskate-park-basics_en. html

Work-Energy Theorem When you throw a ball, you do work on it to give it speed. Fd = 1/2 2 mv You have to do 4 times the work to give the ball twice the speed. Work equals change in kinetic energy. This is the work-energy theorem. Work = ΔKE It takes work to stop a moving object too!

Fd = 1/2 2 mv

Assuming no work has been done, the graph shows: 1) Velocity began at the origin (0, 0). 2) Slope shows constant acceleration. Freefall? Ramp? 3) Since the velocity is increasing, KE=1/2 mv 2. 4) W=Fd If no work, no outside (external) force exerted. 5) Potential Energy transferring to Kinetic energy.

How do you know work was done? W=Fd 1) A bag of groceries is lifted and then placed back in the cart at its original position. 2) An airplane glides to cruising altitude, slowing down as it climbs. (deceleration: no Force applied) 3) A ball, originally at rest, rolls down a ramp and speeds up. (no Force applied) 4) A bowling ball, originally at rest, is thrown down the lane at 12 m/s.

Two boxes with a total mass of 75 N are pushed across a 6 meter long hallway. Was there any work done? If so, how much? Was a push or pull applied? Did the position change? (Did you return to The same place? ) W=Fd W = 75 N *6 m = 450 N

A golf ball that has 650 J is hit into a glass. After colliding with the glass, the ball is moving with 500 J. How much work was done on the ball? 650 J – 500 J = 150 J

A flying pig is pushed with 75 N. It moves in a circle, returning to the initial position. How Much work was done on the pig? (None. No distance was covered. It returned to the same spot. )

http: //www. physicsclassroom. com/Physic s-Interactives/Work-and-Energy/Roller. Coaster-Model/Roller-Coaster-Model. Interactive

Assume each box is 1 J. What is the PE? What is the KE? What is the total energy?

Newton’s Cradle Pair & Share: Talk with a neighbor about Energy Transformations…. .

What type of energy does an airplane have that is flying above the ground? Potential Energy (It has height above the ground. ) Kinetic Energy (It is moving. )

http: //www. physicsclassroom. com/class/energy/Lesson-2/Application-and-Practice-Questions

A pendulum is constructed from a string 1 meter long. The mass is 0. 20 kg. The mass falls a vertical distance of 0. 30 m from the highest to lowest point. Calculate the KE at the lowest point. PE = mgh PE = (0. 2 kg) (10 m/s 2)(. 3 m) PE = 0. 6 J 1 m 0. 20 kg 0. 30 m

If PE=KE, what can you do that will increase the kinetic energy the most? mgh = ½ m v 2 Double ……