Transcript Kinetic Energy

Work

Work
– Work is done on an object when a
force is applied and it moves in a
direction that is parallel to the force
acting on it.
Unit for Work is the Joule
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Work = Force x Displacement
Joule
Newton
Meter
Nm
kg m/s2
m
Work is only done on an object if the force is
parallel to the object’s displacement.
Work = F x cosine Θ x D
Energy
Energy is the ability to do work.
Energy is expressed in Joules.
Work and energy are interrelated.
– Work must done on an object to get to it
move.
– Moving objects can do work.
Positive and Negative Work
– Positive work is done on object when it moves
in the same direction in which the force is
exerted.
The speed of the object increases.
– A student pushes back on the sidewalk to increase the
speed of his skateboard.
– Negative work is done on an object when the
force opposes the forward motion of the
object.
The speed of the object decreases.
– A student uses the brake on his roller blades to slow
down.
Kinetic Energy
Kinetic energy is the energy of motion.
– It can be calculated by using the following
equation.
KE = ½ mv2
Joule = kg x (m/s)2
N = kg m/s2 x m
Nm = Joule
If the object’s mass is doubled then the kinetic
energy is doubled but it the velocity is doubled the
kinetic energy is quadrupled!
Potential Energy
Potential energy is stored energy.
– Anytime a particle or object is forced to maintain a
position in which it would not naturally exist has
potential energy.
– This natiral position is known as equilibrium.
Types of Potential Energy
–
–
–
–
Gravitational Potential Energy
Elastic Potential Energy
Electrical Potential Energy
Chemical Potential Energy
Elastic Potential Energy
The energy stored in an elastic material
Elasticity
Elasticity is the ability of a material to
return to its original shape after being
deformed.
– F = kx
F = Force (N)
k = spring constant (N/m)
x = amount spring or material is stretched or
compresses. (m)
– a negative x means the spring is compressed
– A positive x means the spring is stretched.
Elastic Potential Energy
The amount of elastic energy stored in a
spring.
– Ee = ½ kx2 expressed in Joules
– Ee = elastic potential energy
k = spring constant
x = degree spring is stretched or compressed
Gravitational Potential Energy
PE = mgh
mass x 9.8 m/s2 x height
Work Energy Theorem
Work causes a change in kinetic energy.
Work = Δ energy
W = ½ mv2final - ½ mv2initial
Slowing down or increasing the speed of an
object changes its kinetic energy.
A force must be applied and thus work must be
done to change the kinetic or potential energy of
and object.
Power
Rate in which work is done.
Power is expressed in Watts
– Watts = Joules/second
– 1 horse power = 740 W