Energy Energy is the ability to change or cause change. If there is no energy, there can be no change.
Most of our energy comes from the sun Light from the sun powers all plant growth Plants in turn feed all living organisms (either directly or indirectly) Plants also become our fossil fuels
Potential and Kinetic Energy Potential Energy – Energy of what might happen – Has potential to cause change – Ex. Compressing a spring, a ball lifted above the floor (gravity), etc.
Write these 4 scenarios down and predict which shows Potential or Kinetic Energy? 1.A bow is drawn back. 2.An arrow is shot from the bow. 3.A boulder at rest at the top of a hill. 4.A boulder rolling at the bottom of a hill.
Which Have Potential or Kinetic Energy? PE 1.A bow is drawn back. PE KE 2.An arrow is shot from the bow. KE PE 3.A boulder at rest at the top of a hill. PE KE 4.A boulder rolling at the bottom of a hill. KE
Potential vs Kinetic Potential Energy (E p ) – Increases when mass, gravity or height increases. – If the height doubles, E p doubles Kinetic Energy (E k ) — Increases when mass increases — If the mass doubles, E k doubles — If the velocity doubles, E k quadruples (squared) — What if velocity were tripled?
The total energy is the same at all points of an object’s path
Law of Conservation of Energy Energy can never be created or destroyed. Energy can be converted from one form into another – Kinetic to potential – Potential to kinetic – Kinetic to heat (from friction) Total Energy before = Total Energy after
A falling rock has a potential energy of 750 J and kinetic energy of 450 J. A few seconds later, it has a potential energy of 400 J. Determine its new kinetic energy.
A heavy weight that has a mass of 50 kg is lifted using a rope and pulley to a height of 8 meters above a wood post. The rope is cut and the weight falls to hit the post. What is the speed of the weight on impact? Hint: List the E p and E k for each position of the weight.
A 2,000 kg car moving with a speed of 5 m/sec starts up a hill, and the accelerator and brakes are not working! How high does the car roll before it stops?
A 0.057 kg car starts from rest at the top of a 0.133-meter hill. Find the speed when it reaches the bottom of the hill.
A 500 kg roller coaster car starts from rest at the top of a 60-meter hill. Find the speed when it is halfway to the bottom.