Transcript gravitational potential energy in J

Work is only done by a force on an
object if the force causes the object
to move in the direction of the force.
Objects that are at rest may
have many forces acting on them,
but no work is done
if there is no movement.
Work,
by definition, is
the product of the force exerted on
an object and the distance the object
moves in the direction of the force.
W = F·d
Work is a scalar quantity.
The SI unit of work
is the joule,
named in honor of
James Prescott Joule.
One joule, J, of work
is the work done when
1.0 N of force is applied
through a distance of 1.0 m.
Power,
by definition, is
the time rate of doing work;
or the time rate transfer of energy.
P=W/t
Power is a scalar quantity.
The SI unit of power
is the Watt,
named in honor of
James Watt.
One watt, W, of power
is the power achieved
when 1.0 J of work is done or
1.0 J of energy is transferred
in a time of 1.0 s.
Energy
the ability (capacity) to do work
Energy comes in many forms:
mechanical, electrical , magnetic, solar,
thermal, chemical, etc...
The SI unit of energy is the joule.
Energy, like work and power, is a scalar.
Work-Energy Theorem
the net work done on an object is
equal to its change in kinetic energy
Wnet KE
Kinetic Energy depends on two things:
mass and speed
A cart at rest
has NO
Kinetic energy
Applying a force can give the cart speed, and
therefore kinetic energy.
Applying a greater force
increases the speed and
therefore the kinetic energy
The amount of kinetic energy the cart has is equal to
the amount of work you do to get the cart moving
Increasing the mass also
increases kinetic energy
because it takes even
more force to push.
Kinetic Energy
energy of motion
All moving objects that
have mass have kinetic energy.
KE = 1/2
2
mv
m - mass of the object in kg
v - speed of the object in m/s
KE - the kinetic energy in J
Click here to explore energy, work, and the
Work-Energy Theorem in more depth.
A net force causes
an object to change its KE because
a net force causes an object to accelerate,
and acceleration means a change in velocity,
and if velocity changes, KE changes.
Learn more about the
Work-Energy Theorem
here and here.
Potential Energy
• Gravitational potential energy depends
on an objects mass and height
• Objects with potential energy don’t use
their energy until they start moving.
• The further the object is from the ground
the more potential energy it has
• Chemical potential energy is energy
stored in the form of chemical bonds.
Potential Energy
energy of position or condition
gravitational potential energy
PEg = mgh
m - mass of object in kg
g - acceleration of gravity in m/s2
h - height of object, in m
PE – gravitational potential energy in J
Potential Energy
energy of position or condition
elastic potential energy
PEelastic =
2
½ kx
k – elastic constant in N/m
x - elongation or compression in m
PEelastic – elastic potential energy in J
Click here to investigate elastic constants.