1. Forms of energy

2. The ability to do work What is Energy?
Energy is transferred by a force moving an object through a distance.

3. What Unit is Energy Measured in?
joules J
Remember that work was also measured in joules.
1J = 1kg*m2/s2

4. 2 General Types of Energy
Kinetic energy
Potential energy

5. Energy of motion Kinetic Energy
Depends on the mass and speed of the moving object

6. KE = ½ m v2 Mass in kilograms Speed in m/s Kinetic energy in J

7. KE Practice
A 70.0 kg man is walking at a speed of 2.0 m/s. What is his kinetic energy?
KE = ½ m v2

8. KE Practice
A 70.0 kg man is walking at a speed of 2.0 m/s. What is his kinetic energy?
KE=½ m v2
KE=1/2 (70.0)(2.0) 2
First square the speed.
Then multiply.
½*70.0*4.0=140J
Remember!!!The unit is part of the answer!

9. KE Practice
A 50.0 kg cheetah has a kinetic energy of 18,000J. How fast is the cheetah running?
KE = ½ m v2

10. KE Practice
A 50.0 kg cheetah has a kinetic energy of 18,000J. How fast is the cheetah running?
KE=½ m v2
You are solving for v this time.
√(2KE/m) = v
First multiply 2 * 18,000.
Then divide that number by 50.0.
Last, take the square root of that number.

11. KE Practice √(2KE/m) = v First multiply 2 * 18,000.
Then divide that number by 50.0.
Last, take the square root of that number.
√ 2*18000/50.0=27 m/s

12. Stored energy Objects position or shape give them potential energy.

13. PE=mgh Potential Energy M=mass and g=gravity so mg=weight Mass in kg
On Earth g=9.8m/s2
H=height
Height in meters

14. PE Practice
Suppose the diver at the top of a 10.0 meter high diving platform has a mass of kg. Calculate her potential energy.
PE=mgh

15. PE Practice
Suppose the diver at the top of a meter high diving platform has a mass of kg. Calculate her potential energy.
PE=mgh
PE=50.0*9.8*10.0
G is 9.8 because we assume she is on Earth.
Simply multiply through.
PE=4900J

16. PE Practice
A skydiver with a mass of 68kg is about to jump from an airplane. His potential energy is J. What height is he jumping from?
PE=mgh

17. PE Practice PE=mgh Solve for h. PE/mg=h 3046781/68*9.8
A skydiver with a mass of 68kg is about to jump from an airplane. His potential energy is J. What height is he jumping from?
PE=mgh
Solve for h.
PE/mg=h
/68*9.8
Multiply the bottom numbers first.
Then divide.
H=4572 m