Conservation of energy Potential to kinetic Conservation of energy

Quick review Kinetic energy is the energy of movement Potential energy is the energy of position or condition the equation for PE=mgh Kinetic energy is the energy of movement the equation for KE = ½ mv2 Law of conservation of energy says that energy cannot be created nor destroyed, only changed from one form to another

Check out this video https://www.youtube.com/watch?v=LrRdKmjhOgw Click here for roller coaster conservation of energy

Comprehension check: So _______________ energy pulls the roller coaster car to the top of the first hill. At the top of the first hill, the coaster has ________________ potential energy. During the first downhill run, the Potential is gradually converted to __________________ and at the bottom of the first hill, there is __________ potential energy left. At the bottom of the first hill, the coaster has ________________ kinetic energy.

Comprehension check: In a world with no friction, pe at the top of the hill and KE at the bottom of the hill would be ___________. Energy is conserved. In the real world, some energy is lost to __________ energy from friction, and _________ energy as the coaster rolls on the track. This means that the second hill is always __________ than the first hill. (in the real world)

A visual explanation: https://www.youtube.com/watch?v=87E0DKs5bok Click here to see a visualization of this transfer of pe to ke Make sure to click on the explanation after the video finishes

One last story: Click here to listen to the story / explanation https://www.youtube.com/watch?v=7K4V0NvUxRg Click here to listen to the story / explanation

What did you learn? Write a note or two

Mini quiz:

1- If a 20.0 Kg child + swing is raised to a distance of 2.0 m from the sand, then released, calculate the: (assume no air resistance) Potential Energy at the top of the swing arc Kinetic Energy at the top of the swing arc Total Energy at the top of the swing arc

1- PE at top: PE top = mgh = (20.0 kg) (9.8 m/s2) ( 2.0 m) = 392 J = 400 J Since the swing is not moving at the top, it has 0 velocity and 0 KE Total Energy is PE + KE = 400 J + 0 J = 400 J

2- If a 20.0 Kg child + swing is raised to a distance of 2.0 m from the sand, then released, what is the total kinetic energy at 1.0 m above the sand?

200 J = KE at 1.0 meters above sand 2- If a 20.0 Kg child + swing is raised to a distance of 2.0 m from the sand, then released, what is the total kinetic energy at 1.0 m above the sand? (Assuming no friction) At this point, some of the potential energy at the highest spot has been converted to kinetic energy, so PE top - PE at 1.0 m = KE at 1.0 m 392 J - (mgh) = KE 392 J - (20.0 kg) (9.8 m/s2) ( 1.0 m) = KE 392 J - 196 J = KE 196 J = KE 200 J = KE at 1.0 meters above sand

3- A 0.5 Kg hammer drops on a concrete floor of a skyscraper under construction from 19.6 m high. Determine the kinetic energy of the hammer just before it hits the concrete. (assume no friction)

KE just before impact = PE at the top = mgh A 0.5 Kg hammer drops on a concrete floor of a skyscraper under construction from 19.6 m high. Determine the kinetic energy of the hammer just before it hits the concrete. (assume no friction) KE just before impact = PE at the top = mgh = (0.5 kg) (9.8 m/s2) (19.6 m) = 96.04 J = 100 J

4- A pendulum with a mass of 3 kg swings at the end of a chain. At the top of the arc, it has a PE of 40 J. At the very bottom of the swing, it has a velocity of 4 m/s. This is the real world, and some energy will be converted to sound and heat. Calculate the KE at the bottom of the arc Energy used to do work Total Energy of the system

A pendulum with a mass of 3 kg swings at the end of a chain A pendulum with a mass of 3 kg swings at the end of a chain. At the top of the arc, it has a PE of 40 J. At the very bottom of the swing, it has a velocity of 4 m/s. This is the real world, and some energy will be converted to sound and heat. Calculate the KE at the bottom of the arc KE = ½ mv2 = ½ (3 kg) (4 m/s)2 = 24 J

A pendulum with a mass of 3 kg swings at the end of a chain A pendulum with a mass of 3 kg swings at the end of a chain. At the top of the arc, it has a PE of 40 J. At the very bottom of the swing, it has a velocity of 4 m/s. This is the real world, and some energy will be converted to sound and heat. Calculate the KE at the bottom of the arc Energy for Work = PE top – KE bottom = 40 J - 24 J = 16 J = 20 J

A pendulum with a mass of 3 kg swings at the end of a chain A pendulum with a mass of 3 kg swings at the end of a chain. At the top of the arc, it has a PE of 40 J. At the very bottom of the swing, it has a velocity of 4 m/s. This is the real world, and some energy will be converted to sound and heat. Calculate the KE at the bottom of the arc Total energy of the system is the original PE it was given when the pendulum was raised. 40 J