Download Ch 6 Work, Power, Energy

Energy
Ch 6 Work, Power, Energy
Potential Energy

Energy that is stored
◦ Potential for doing work

Depends on object AND environment

Examples:

Type of potential energy
stretched rubber band, rock on edge of cliff,
food we eat, electric batteries, fuels
◦ Gravitational Potential Energy
◦ Elastic Potential Energy
◦ http://www.youtube.com/watch?v=Jnj8mc04r9E&feature=related
Gravitational
Potential Energy



An object with the potential to fall
Stored energy
depends on mass, gravity and height
Equation:
 EP or PEg = m g h
Potential Energy gravitational (joules) =
mass (kg)*acceleration due to gravity(m/s2)* height (m)

Units –joules or Newton*meter

Example
 Dropping book 1mm above foot vs 1 m above foot
Kinetic Energy
•
Energy of motion
• If an object is not in motion, No Kinetic Energy
◦ If you roll a bowling ball and beach ball at the same
speed, they still have different KE because of their
masses
Equation:
Depends on mass and speed
• EK or KE = ½ m v2
•
•
•
•
Kinetic Energy (joules) = ½ * mass (kg) * speed2 (m/s)
Think Speed (not velocity – direction is ignored)
Units – can be joules or Newton*meter
Potential Energy converts to Kinetic
energy ….
Example Problem 1
A tennis ball is falling 20 m. The total
Mechanical Energy is 100J.
Part A
Part B
50 J
50 J
Part C
80 J
Part D
0J
100 J
Total Mechanical Energy

Sum of all forms of potential energy and
Kinetic Energy of an object
totalEM=EK+Σ
EP
-Σ means SUM of
-total Mechanical Energy (EM) = Kinetic Energy (EK) plus the
sum of Potential Energy (EP)
Conservation of Energy
•
Energy is always conserved in one form or another
Energy cannot be created or destroyed, only change
forms
•
•
Bowling Ball Video http://www.youtube.com/watch?v=BVxEEn3w688
Conservation of Energy

MEi = MEf
◦ So (PEi + KEi = PEf + KEf)

When is it not conserved???
◦ The mechanical energy lost to friction is
changed to heat energy
◦ Total energy is still conserved
Type of Potential Energy
Elastic Energy
 Energy that is stored due to being
stretched or compressed is called elastic
(spring) energy

Like slingshot or bungee cord
Elastic potential energy