1. Regents Physics Mr. Rockensies

2. How does energy manifest itself physically?

3. Energy is the ability to do Work. Energy exists in several different forms. Almost all energy on Earth can be traced back to the Sun. Examples: Mechanical, Thermal (Heat), Chemical, Nuclear, Electromagnetic, Kinetic, Potential

4. Work is a measure of the amount of energy used to move an object. Mathematically: Work = Force displacement Because we are multiplying two vectors, we end up with a scalar quantity – Work is a scalar quantity. Work is only done when the Force and the displacement are in the SAME direction.

5. Unit for work: Work = F d = Newtonm To simplify this, we use Joules (J). 1 J = 1 Nm All energy quantities will be measured in Joules.

6. Work and Friction When friction is present, energy in a system is lost because of it. When two objects come into contact and move past each other, energy is given off in the form of HEAT – this is due to FRICTION.

7. Power is the rate at which energy is used, transformed, or transferred. Power = Work/time AND Power = Velocity Force Power = Force Distance time Units: Watts = Joules/second = N m = kg m 2 s s 3 We measure Power in Watts to simplify the units

8. A measure of the amount of energy expended by the average horse over a given period of time. One horsepower is equal to 746 Watts, but depending on how you are using horsepower, it is up for debate.

14. Energy cannot be created or destroyed; it can only change forms.

15. E i = E f PE i = PE f + Ke f mgh i = mgh f + 1/2mv f 2 gh i – gh f = v 2 /2 ΔhiΔhi ΔhfΔhf m m initial final vfvf If an object starts from some initial height and enters free fall, its initial Potential Energy will equal the sum of its final Potential Energy and Kinetic Energy

16. Because energy is a scalar, direction doesn’t matter, and this works for curved motion as well hihi m m hfhf vfvf

17. A B C E A = E B = E C PE A + KE A = PE B + KE B = … hAhA hChC

18. v i = 0 Ke i = 0 All PE v f is max KE is max No PE E top = E bottom PE = KE

19. E i = E f Pe s = Ke cart 1/2kx 2 = 1/2mv 2 PE = 1/2kx 2 KE = 1/2mv 2

20. Initial Mechanical energy (PE + KE) becomes final mechanical energy plus some internal energy, converted by friction. (PE + KE + Q) height reached with no friction height reached with friction Q = internal energy, usually heat, caused by friction

21. In a closed isolated system, what happens to the gravitational potential energy of an object as it falls? the kinetic energy? the total energy? Does the amount of energy an object has change if the object changes direction? How does Potential Energy change if a spring is compressed more? When is Kinetic Energy the greatest for a swinging pendulum?