Download Potential and Kinetic Energy

Potential and Kinetic Energy
• Energy: is the
ability to do work
Kinetic Energy
= the energy an object possesses
because of its motion
• The amount of Kinetic energy is
dependent on the mass of the object in
motion and it’s velocity.
VELOCITY
Velocity = distance ÷ time
Distance = meters
Time = seconds
Calculating kinetic energy
If we know the mass of an object and its velocity
we can determine the amount of kinetic energy
possessed by using the following formula:
kinetic energy = 1/2 (mass of object)(velocity of
object)2
or KE = 1/2 mv2
or KE = 0.5mv2
The SI unit for kinetic energy is the Joule (J).
A Joule is kg  m2/s2
A bicycle with a mass of 14 kg
traveling at a velocity of 3.0 m/s
east has how much kinetic
energy?
KE = 0.5mv2 = 0.5(14 kg)(3.0 m/s)2
= 0.5(14 kg)(9.0 m2/s2)
= 63 kg x m2/s2 = 63 J
A 1200 kg automobile is traveling
at a velocity of 100 m/s northwest.
What is the kinetic energy of the
automobile?
KE = 0.5 mv2 = 0.5(1200kg)(100 m/s)2
= 0.5(1200 kg)(104 m2/s2)
= 6 x 106 kg  m2/s2 = 6 x 106 J
Potential Energy
• The energy of position
• The amount of energy contained in an
object at rest
Determining Potential Energy
• By its position and its weight (mass X
gravity)
PE = (mass)(gravity)(height) = mgh
• where m is mass in kg
• g is the force of gravity = 9.8 m/s2
• h is the height
• The SI unit that represents potential
energy is the Joule (J) (kg  m2/s2).
Examine an example of
potential energy
A flower pot with a mass of 15 kg is sitting
on a window sill 15 meters above the
ground. How
much potential energy does the flower pot
contain?
• PE = (mass)(gravity)(height)
• = (15 kg)(9.8 m/s2)(15 m)
• = 2205 kg  m2/s2
• = 2205 J
• = 2.2 x 103J
Examine an example of
potential energy
• If the flower pot is lowered to a window sill
that is 10. m from the ground. Does this
change the potential energy of the flower
pot?
PE = (mass)(gravity)(height)
= (15 kg)(9.8 m/s2)(10. m)
= 1470 kg  m2/
= 1470 J
= 1.5 x 103J
Potential or Kinetic Energy?
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Moving car
Tree branch
Bent car fender
Balloon filled with air
Balloon squirting around room
Person inside a moving car
• What type of
energy does the
space shuttle
have at lift off?
Conversion of Potential to Kinetic
Energy
• In this picture
both kinds of
energy are
evident. Can you
point them out?
• The water at the
top has potential
energy
• When water falls
to a lower level,
the potential
energy is
converted to
kinetic energy.
Example