LAW OF CONSERVATION OF ENERGY

 #1: What caused the penny to go up into the air?  What did you have to do to make sure it went almost up to the ceiling without hitting it?  #3-5: What happened to the deflection as the ball was rolled from a higher distance?  #6-9: What happened as you increased the deflection of the ruler from 2 cm to 6 cm?

 A force can change the position and speed of an object in a way that allows the position and speed to change back to how it was originally  What allows for this?

Law of Conservation of Energy – energy cannot be created or destroyed; it can be transformed from one form to another, but the total amount of energy remains constant Kinetic Energy – energy associated with motion; KE = ½ mv 2 Potential Energy – energy associated with position Gravitational Potential Energy – the energy an object possesses because of its vertical position from Earth; GPE = mgh Elastic Potential Energy – the energy of a spring due to its compression or stretch; EPE = ½ kx 2

 In Case You Missed it: ENERGY CANNOT BE CREATED OR DESTROYED! IT IS TRANSFORMED FROM ONE FORM TO ANOTHER!  Total Energy = Kinetic Energy + Potential Energy

 Review: What must happen in order for an acceleration to occur?

Work – the product of the displacement and the force in the direction of the displacement; W=Fd Law of Conservation of Energy – energy cannot be created or destroyed; it can be transformed from one form to another, but the total amount of energy remains constant Kinetic Energy – energy associated with motion; KE = ½ mv 2 Potential Energy – energy associated with position Gravitational Potential Energy – the energy an object possesses because of its vertical position from Earth; GPE = mgh Elastic Potential Energy – the energy of a spring due to its compression or stretch; EPE = ½ kx 2

Work: W=Fd; W = Work (Nm), F = Force (N), d = distance (m) Elastic Potential Energy: EPE = ½kx 2 ; EPE = Elastic Potential Energy (Nm), k = spring constant (N/m), x = amount of bending (m) Gravitational Potential Energy: GPE = mgh; GPE = Gravitational Potential Energy (Nm), m = mass (kg), g = acceleration due to gravity (m/s 2 ), h = height through which object is lifted (m) Kinetic Energy: KE = ½mv 2 ; KE = Kinetic Energy (Nm), m = mass (kg), v = speed (m/s) Newton: kgm/s 2 Nm = Joule (J)

 One way to think about energy is to consider it as “stored work”

 Let’s try to identify the different kinds of energy  Coin Toss  After you bent the ruler, but before you let it go:  After you let it go (rising), and before it hits the ground (falling):  At the peak (the highest the coin will go up before it starts to come back down; hint: v = 0 m/s)

 Let’s try to identify the different kinds of energy  Pole Vault  While the pole vaulter is running  When the pole vaulter uses the pole to spring herself up (bends pole)  When the pole vaulter is in the air and rising  When the pole vaulter is no longer rising, but has not started falling yet  When the pole vaulter is falling down

 Child has 28 blocks (possibly in the middle of the floor in her bedroom)  Sometimes one or two blocks are elsewhere (mom and dad’s room, living room), but there are still 28 blocks total

 A weightlifter uses a force of 325 N to lift a set of weights 2.00 m off the ground. How much work did the weightlifter do?  Want  Given  Formula  Solve (units)

 How much energy is stored in a pole with a spring constant of 15 N/m if it is deflected 1.6 m?  Want  Given  Formula  Solve (units)

 One of the highest pop flies every recorded in baseball was about 172 m. What is the gravitational potential energy of a baseball with a mass of 145 g that is hit that high into the air (g = 10 m/s 2 )?  Want  Given  Formula  Solve (units)

 A football player has a mass of kg and runs at a speed of 6.0 m/s. What is his kinetic energy?  Want  Given  Formula  Solve (units)

 If champion pole vaulters can clear a 6.0 m high bar with a 5.5 m long pole, why can’t they vault over a 12 m high bar with a pole 11.0 m long?  What factors (variables) do you think limit the height a pole vaulter has been able to attain?