Transcript Energy & Conservation of Energy Notes

7.2 Energy
What is Energy?
Energy is the ability to do work.
It measures the ability for things to move or
cause a change in matter
Examples:
changes in temperature, speed, position,
pressure, or any other physical variable.
Some Forms of Energy
Units of Energy
Pushing a 1 kilogram object with a force of
one newton for a distance of one meter uses
one joule of energy.
1 J = 1 N•m
Potential Energy
Potential energy: energy due to position.
Usually due to height!
Think of as “potential to fall”
Highest EP
Lowest EP
Potential Energy
EP = mgh
gravity (9.8 m/sec2)
Potential Energy Example
What is the potential energy of a 4 kg cat crouched
in a tree 3 m off the ground?
Potential Energy Example
What is the potential energy of a 10kg baseball
that is 2m off the ground?
Kinetic Energy
Kinetic energy: energy due to motion
The kinetic energy equals the
work the object can do by
exerting force as it stops.
Kinetic Energy Example
What is the kinetic energy of a 10 kg dog
running at 5 m/s?
Kinetic Energy Example
What is the velocity of a 50 kg pterodactyl
flying with a kinetic energy of 90,000 J?
7.2 Conservation of Energy
Energy Flow
Kinetic energy can be
converted into potential
energy and vice versa.
Conservation of Energy
 The Law of Conservation of Energy says that
energy cannot be created/destroyed, just changed.
Total energy before = total energy after
Conservation of Energy Example
When you throw a ball in
the air, the energy
transforms from kinetic to
potential and then back to
kinetic.
Conservation of Energy Example
A 0.5 kg ball moving at a speed of 3 m/s rolls
up a hill. How high does the ball roll before it
stops?
Conservation of Energy Example
A 800kg roller coaster cart is at the top peak of
Valley Fair’s Wild Thing (60m drop!). At the
bottom of the drop, what will its velocity be?
(assume all energy is converted to kinetic energy)
Potential & Kinetic Energy Example
A 2 kg rock is at the edge of a cliff 20 meters above a
lake. The rock becomes loose and falls toward the
water below. What is the potential energy and the
kinetic energy of the rock at the top of the hill and
when it is halfway down? Its speed is 14 m/s at the
halfway point.
Potential (top) =
Potential (halfway) =
Kinetic (top) =
Kinetic (halfway) =