 # Energy Every observable change requires energy.

## Presentation on theme: "Energy Every observable change requires energy."— Presentation transcript:

Energy Every observable change requires energy.
Energy comes in several different forms (food, electrical, solar, chemical), and can be converted from one form to another.

Kinetic energy Energy associated with motion KE = ½ mv2
units are Joules mass MUST be in kg velocity MUST be in m/s Example: What is the kinetic energy of a baseball moving at a speed of 40 m/s if the baseball has a mass of 0.15 kg? KE = ½ mv2 KE = ½ (0.15 kg)(40 m/s)2 KE = 120 J

Potential Energy: The energy stored in motionless objects Four types: 1. Elastic potential energy 2. Chemical Potential Energy Stored by something that can stretch or compress Energy is released when the object is allowed to return to its normal state Chemical bonds store energy. Breaking the bonds releases the energy

3. Electrical and Nuclear Potential Energy
4. Gravitational Potential Energy Electrical-stored energy due to the position of electrical charges. Nuclear-energy stored in the nucleus of an atom Anything that can fall has stored GPE GPE = mgh m = mass in kg g = gravitational acceleration (9.8 m/s2) h = height above the ground The higher above the ground something is, the greater the GPE EX: Find the height of a baseball with a mass of 0.15 kg that has a GPE of 73.5 J. GPE = mgh 73.5 J = (0.15 kg)(9.8 m/s2)h h = 50 m

Conservation of Energy: Energy is neither created nor destroyed as is changes from one form to another GPE = mgh = (2 kg)(9.8 m/s2)(10 m) = 196 J 2 kg KE = 0 J h = 10 m While the energy has changed form, the amount of energy has not changed. Energy has been conserved. KE = ½ mv2 = 196 J 2 kg GPE = 0 J

3 kg GPE = (3 kg)(9.8 m/s2)(8 m) = 235 J 8 m KE = 0 3 kg GPE = (3 kg)(9.8 m/s2)(6 m) = 176 J 6 m KE = 235 J J = 59 J GPE = (3 kg)(9.8 m/s2)(4 m) = 118 J 3 kg 4 m KE = 235 J J = 118 J 3 kg GPE = (3 kg)(9.8 m/s2)(2 m) = 59 J 2 m KE = 235 J - 59 J = 176 J GPE = 0 J 3 kg KE = 235 J

3 kg 8 m 3 kg 6 m 3 kg 4 m 3 kg 2 m 3 kg KE = 0 v = 0 KE = 59 J
= ½(3 kg)v2 6 m v = (2*59/3) = 6.3 m/s 3 kg KE = 118 J 4 m v = (2*118/3) = 8.9 m/s 3 kg KE = 176 J 2 m v = (2*176/3) = 10.8 m/s 3 kg KE = 235 J v = (2*235/3) = 12.5 m/s

Mechanical Energy = KE + GPE
GPE = max KE = 0 GPE = max KE = 0 GPE = 0 KE = max Q: Why does a real pendulum stop swinging? A: Because friction converts some of the mechanical energy into thermal energy.

E = mc2 During nuclear fusion, some of the mass of the fusing nucleii is transformed into energy. H 1 2 3 + He 4 neutron + Energy