1. Work & Energy

2. Work Work is the result of applying a force over a distance.
When you lift a book 1 m into the air from the table, you have done work.
The amount of work depends on the distance traveled and the magnitude of the force
You do more work lifting 5 books than just 1 book

3. Energy Energy is the ability to do work.
You eat a bowl of Wheaties to get energy to accomplish work.
The energy we will focus on will have two variations – Potential and Kinetic

4. Potential Energy (P.E.)
A student with a high IQ has the potential to do well in school – does he always do so? No! He has the potential
Potential energy is similar – it is stored and has the potential to make something happen
A rollercoaster at the top of the ride has the potential to roll down
A cup of gas has the potential to burn

5. Potential = stored, in place
Chemical, Gravitational, and Elastic are three common variations of potential energy

6. Calculation P.E.
The potential of any object due to gravity will depend on the mass of the object and the height of the object
A heavy book has the potential to hurt more when it falls on your hand
A book high up has the potential to hurt more than a book just above your hand
PE = mgh
M = mass (kilograms), g = gravity(m/s2), h = height (meters)
PE is measured in Joules (J)

7. Lets Practice
What is the potential energy of a 700 kg car at the top of a 20 m hill?
PE = mgh
PE = (700 kg)(9.8m/s2)(20m)
PE = 137,200 J
What is the P.E. of a 2 kg book 1.5 m above the floor?

8. Kinetic Energy
Just as kinetic friction dealt with friction in motion, kinetic energy deals with objects in motion
Just like P.E., K.E. will depend on the mass – more mass means more K.E.
The second factor in K.E. is velocity
The more velocity, the more energy
K.E. = ½mv2
m = mass (kilograms), v = velocity (m/s)

9. Lets Practice What is the K.E. of a 700 kg car moving 4 m/s?
KE = ½ mv2
KE = .5 (700 kg) (4 m/s)2
KE = 5600 J
What is the K.E. of a 300 g baseball thrown at 30 m/s?

10. Identify the type of energy (PE or KE)
A falling skydiver
A stretched rubberband
A flying rubberband
A book on the top shelf
A person walking
A waterfall

11. Which has more energy? A person running or walking?
A child and an adult riding bikes at the same speed?
A football player on a diving board or a gymnast on the same diving board?
A baseball or a shot put?