Work, Energy, and Power
There are a lot of
advantages of knowing
some physics but this one
is definitely not one of
them.
Potential Energy PE (Ug)
An object can
store energy as
the result of its
position.
Potential Energy PEgrav or
Ug
Ug = PEgrav = mass * g * height
Gravitational potential
energy is the energy
stored in an object as the
result of its vertical
position (i.e., height).
Ug = PEgrav = m * g * h
m = mass of object (kg)
g = gravity = 10m/s^2
h = height (m)
Unit: Joules (J)
Kinetic Energy
Kinetic energy is
the energy of
motion.
m = mass of object
v = speed of object
Unit: Joules (J)
The Joule is the unit of work and energy.
1 Joule = 1 Newton * 1 meter
1J = 1 N * m = (Nm)
Hoping to replace steam engines by
electric motors, his first research sought to
improve electric motor efficiency. His
investigations concerned themselves with
James Prescott Joule the production of heat.
Great Britain (1818-1889)
Mechanical Energy
ME = PE + KE
Unit: Joules (J)
ME = PE + KE
The total amount of
mechanical energy
is merely the sum
of the potential
energy and the
kinetic energy.
Work W= F*d
Work is the energy expended to move something.
If there is no motion, no work has been done no matter how
much force is applied.
In physics, work is
defined as a force
acting upon an
object to cause a
displacement.
The Joule is the unit of work.
1 Joule = 1 Newton * 1 meter
1J = 1 Nm
Work- Energy Theorem
Energy is conserved
Energy Transformation for Downhill
Skiing
Roller Coaster
Energy Transformation on a Roller
Coaster
Energy Transformation for a
Pendulum
Power P P = W/t
Power is the rate
at which work is
done.
Unit: J/s = W (Watt)
James Watt (1736-1819)
James Watt dies, age 83,
healthy, happy, and famous
1781-1802 Patents
steam engine
In 1782 a sawmill ordered
an engine that was to
replace 12 horses.
James Watt was born in
1736 in Greenock,
Scotland. James was a
thin, weakly child who
suffered from migraines
and toothaches. He
enjoyed mathematics in
grammar school, and also
learned carpentry from his
father.
The standard metric unit of power is the Watt.
Unit: W (Watt)
One horsepower is equivalent to
approximately 750 Watts.
Formulas
PE = Ug = m*g*h
(J)
KE= ½*m*v2
(J)
W = F*d
(J)
P = W/t P = (F * d)/t
(J/s or Watt)
P= F*v
(J/s or Watt)
ME= KE+PE
(J)
Hint: to make kg to a “Force” use W= F = m* g
g=10
Formulas
Impulse
I = F*t
(Ns)
Momentum
p = m* v (kg*m/s)
Impulse = change in momentum I = p
Impulse-Momentum
F*t = m*v
Conservation of momentum
m1 * v1 = m2 * v2