Download What is ENERGY?

April 7, 2009
• Study for 5 min for your quiz.
• You need: Calculator and Writing Utensil
• When you are done with quiz: Bring it up
and pick up a note sheet for Energy!
Goals
• To explain different types of energy
• To calculate potential and kinetic energy
Q: What is ENERGY?
• Energy is….
– the ability to do work
– a measure of how much work is done
– a word to describe the power and effort
of a force.
– measured in Joules
ENERGY
• Energy is the ability to do work
• Doing work uses energy
• An object can gain energy if work is
done on it
Q: What is ENERGY?
• Two MAIN types of mechanical energy:
– Potential energy
– Kinetic Energy
Q: What is POTENTIAL
ENERGY?
 Potential Energy (PE) is stored energy
• Coaster has PE when it is at the top of the
hill. Even if it isn’t moving yet, it may if a
force is applied and it begins to move
Q: What is POTENTIAL
ENERGY?
• Gravitational potential energy (GPE) is the energy
of an object due to its position above the surface
• GPE = mgh = wh
• m=mass (in Kg)
• g=acceleration due to gravity … 9.8 m/s2
• h= height (in m)
• w = weight (N)
• UNITS:
“Homework”
• Complete the Practice Problem for PE on
your note sheet!
PRACTICE PROBLEM: Find the PE
of a rock climber as she climbs 35
m above the base of a cliff. Her
mass is 65 kg.
•
Given:
h = 35 m
m = 65 kg
g = 9.8 m/s2
GPE = ?
• Equation:
GPE = m x g x
h
• Solve: GPE =
65 kg x 9.8 m/s2 x 35m
=22,295 J
Q: What is KINETIC
ENERGY?
• Kinetic Energy (KE) is the energy due to an
object’s motion
– Active energy
– A rock as it falls off of a cliff
• Formula: KE = ½ * m * v2
– m= mass (kg)
– v = velocity (m/s)
• UNITS:
PRACTICE PROBLEM:
What is the KE of a 44 kg
Cheetah running at 31 m/s?
• Given:
– m = 44 kg
– v = 31 m/s
– KE = ?
• Equation:
KE = ½ * m * v2
•Solve: KE =
(1/2) (44 kg) (31
m/s)2
21,142 J
Homework
• Kinetic and Potential Energy WS