Transcript ENERGY Energy Notes 2

Energy
The ability to do work.
Unit = J
Joule – relates to calorie
1 cal = 4.15 J
Potential Energy
• The stored energy of position.
PE = mgh
• The higher off the ground object
is, the more potential it has to do
work.
Potential Energy
• Potential Energy is energy of position.
• An object gets potential energy from
height, mass and gravity.
• An object with potential energy has the
potential to do work. This potential is
only released if the object falls.
• The energy is then transformed into
energy of motion or transformed into work.
Potential Energy
• Potential energy
helps us generate
electricity in
hydroelectric dams.
When the water falls,
gravity helps turn
energy of height to
electrical energy.
Potential Energy
Kinetic Energy
• The energy of motion
KE = ½
2
mv
• The faster an object is moving,
the more ability it has to do work.
• http://www.youtube.com/watch?v=qZ4FFWvZtyo
Kinetic Energy
• Kinetic Energy is energy of motion.
• An object gets kinetic energy from its
mass and velocity.
• An object with kinetic energy has energy
stored in motion.
• When the object slows down the energy is
released into potential energy (if going up)
or some other kind of energy (like heat
[thermal energy] in the brakes of car).
Kinetic Energy
Kinetic Energy
The Law of Conservation
of Energy
• Energy cannot be created or
destroyed.
• It merely transforms from one
form to another.
Problems
10kg
1. What is the work done to lift a
10kg box to a height of 5m?
2. What is the box’s potential energy
once it is there?
3. If the box is dropped, what is the
PE halfway down (at 2.5m)?
4. A 8 kg cat is running 4 m/s. How
much kinetic energy does it have?
5. A 4 kg bird has 8 joules of kinetic
energy. How fast is it flying?
Mechanical Energy
• Mechanical Energy is the sum of all the
kinetic energy and potential energy in a
system.
• Formula M = K + U
• K = Kinetic energy
• U = potential energy
• Unit- J