• There are 6 basic types of simple machines.
Simple machines are the most basic tools
used to decrease force while increasing
distance. They are:
– The Lever
– The Pulley
– The Inclined Plane
– The Wedge
– The Screw
– The Wheel and Axle
• Levers are simple machines that involve a
rigid arm and a fulcrum. The fulcrum is
the point about which a lever pivots.
“Give me a place to
stand and a lever
long enough, and I
will move the world.”
Class 1: Input (effort) is on
opposite side of fulcrum from
Class 2: Effort (input) is farther
from fulcrum than load
Class 3: Effort (input) is closer
to fulcrum than load (output).
This lever is does not have
much mechanical advantage.
• Pulleys are devices that change the direction
of tension in a rope or wire.
allow you to
over a greater
• Inclined planes are
useful because they
require less force to
ascend. What sorts
of situations might
you expect to see
• What is the mechanical advantage to the
inclined plane shown below?
• Wedges are essentially
• An axe blade is a great
example of a wedge.
• A screw is a central
axle with a helical
• Rotary force is
• Some car jacks work
on the principle of a
• A wheel is a circular
device which rotates
around a central pivot
called an axle.
• When you turn a
steering wheel, you
exert relatively little
force, but large
amounts of force are
felt closer to the axle.
Why do you think
truckers have such big
• Mechanical energy is generally classified in two
– Kinetic energy – energy associated with movement.
Examples: running, car moving, a ball thrown with a
– Potential energy – energy associated with temporary
storage of mechanical. That is, it has the “potential” to be
converted to kinetic. Examples: a rubber band wants to
move when stretched; a ball wants to fall off a tall building
b/c it possesses gravitational potential energy.
• To measure energy, the SI unit we use is the
Joule. This is the equivalent energy needed to
exert a force of 1 N over a distance of 1 m.
• Other units of energy include the kWhr, eV,
Calorie, BTU, and even the erg.
• Energy is NOT to be confused with Power!
Power is the dissipation of energy over time.
Without a time description, one cannot have
• Objects that have mass and move at a non-zero
speed have kinetic energy. The amount of this
energy is supplied by a simple equation:
• 1.) If you have an object with a mass of 3kg that
moves at a constant speed of 5 m/s, what is the
kinetic energy associated with this movement?
• 2.) If you triple an object’s speed, what happens to
its kinetic energy?
• When you have a mass at any height above the Earth’s
surface, what happens to the mass when it is released? Why?
• We like to describe the energy that is available to masses by
putting them at given heights above Earth’s surface by
gravitational potential energy.
• For example, when an object falls from a building, it begins
with a height (and gravitational potential energy). As it falls,
that potential energy is directly converted to kinetic. At the
bottom of the fall, the object now has zero gravitational
potential, because it has all converted to kinetic, and there is
no more height to supply additional potential.
• We have a simple equation for gravitational
potential energy near Earth’s surface:
This equation is only valid for situations in which objects are close to
Earth’s surface. This is b/c when we move away from Earth, the
gravitational force decreases exponentially.
• We can actually prove this equation based on our
knowledge of work:
Say you pull an object from the reference level
shown such that the object moves at a constant
speed (equilibrium). The amount of work performed
by our pull force is:
W F d mg h mgh
• 1.) A diver jumps off a 10-m
platform. Assuming the diver
“weighs” 52 kg, what is his or her
potential energy on the platform?
• 2.) What is his or her potential
energy when he or she reaches a
height of 7 m?
• 3.) 5m?
• 4.) The water?
• Anytime there is frictionless “freefall”
occuring, potential is converted directly into
kinetic. There is no energy lost: the first law of
thermodynamics. One cannot create or
• That is, the sum of kinetic and potential must
always add to a constant, mechanical energy