Transcript Energy and Work

Energy and Work
Work…
Work = Force
//
x Displacement
Rights belong to Universal Pictures
and the writers of Despicable Me.
W = F// x d
** Remember that displacement is the distance AND
direction that something moves. It is a vector quantity. It
has magnitude and direction.
Start
End
Facts about Work…
Measured in Newton meters
(Nm) or Joules (J)
Work is parallel to
displacement
The symbol for work is W
Working or Not??
Work only happens if the forces
acting on the object are
unbalanced.
Balanced forces = NO work
Work does not happen if the
object is returned to its original
position.
Why work?
Work can change the potential
energy of an object. When you lift
something against the force of
gravity, you are increasing the
height of the object and increasing
its potential energy.
The amount of work done to an
object is equal to the object’s
change in kinetic energy.
How are energy and work related?
Energy is the ability to do work
Work is done when the kinetic
energy is changed
Anytime something accelerates,
it is doing work
What is Energy?
Energy is the
property that
enables something to
do work.
What is kinetic energy?
Kinetic energy is the
energy of motion.
KE =
2
1/2mv
What happens if…
KE =
1/2mv2
 What happens if you double the mass?
 What happens if you double the velocity?
 What happens when you half the mass?
 What happens when you half the velocity?
Kinetic Energy Example…
A 75 kg skater is moving at 20 m/s across the concrete.
How much KE does the skater have?
Potential energy
Gravitational Potential Energy (PEg)
is the amount of work an object can
do because of its height
Elastic Potential Energy (PEelastic) is
the amount of work an object can
do because of its position
Gravitational Potential Energy
PEg = mass (kg) x acceleration due to gravity (9.8m/s2) x height (m)
PEg = mgh
PEg will be measure in Joules
Wile E. Coyote is 2 m above the ground and has a mass of 50 kg.
What is his PEg?
Who has more PEg?
Now who has more PEg?
Elastic Potential Energy
PEelastic=1/2 kx2
K = the spring constant (related to the strength of the
spring)
X = the amount the spring is stretched or compressed from
equilibrium
Elastic Potential Energy
Wile E. Coyote compressed his Acme giant spring 5 m. The
instruction book stated that the spring constant is 3x103
N/m. How much elastic potential energy has Wile E.
Coyote stored in the compressed spring?