Simple Machines
Work and Machines
- Simple machine: machine that does work with only one movement of the machine.
There are six types of simple machines: lever, pulley, wheel and axle,inclined plane, screw, and
wedge. The pulley and the wheel and axle are modified levers, and the screw and the wedge
are modified inclined planes.
- Lever: simple machine consisting of a bar free to pivot around a fixed point called the fulcrum.
There are three classes of levers and the differences among the three classes of levers depend
on the location of the fulcrum, the input force and the output force.
A. First-class lever: lever with the fulcrum located between between the input and output
forces. The output force is always in the opposite direction to the input force in a first-class
lever.
B. Second-class lever:
lever where the output
force exerted is
between the input
force and fulcrum. For
a second-class lever,
the output force is
always greater than
the input force.
C. Third-class lever:
lever where the input
force is applied
between the output
force and the fulcrum.
The output force is
always less than the
input force in a thirdclass lever, but the
distance over which
the output force is
applied is increased.
IMA of lever = length of input arm / length of output arm
Mr. Saoulis
- Pulley: simple machine that consists of a grooved wheel with a rope, chain, or cable running
along the groove p; can be either fixed or movable.
The system of pulleys consisting of fixed and movable pulleys is called a block and tackle. The
IMA of a block and tackle can be increased by increasing the numbers of pulleys in the pulley
system.
Mr. Saoulis
- Wheel and axle: simple machine that consists of a
shaft or axle attached to the center of a larger wheel,
so that the shaft and the wheel rotate together.
Examples of wheel and axles are doorknobs,
screwdrivers, faucet handles, and gears. Usually the
input force is applied to the wheel, and the output force is
exerted by the axle.
IMA = radius of wheel / radius of axle
- Inclined plane: simple machine that consists of a sloping surface, such as a ramp, that
reduces the amount of force needed to lift something by increasing the distance over which
the force is applied.
IMA of inclined plane = length of slope / height of slope
- Screw: simple machine that consists of an inclined plane
wrapped around a cylindrical post.
The IMA of a screw is related to the spacing of the threads, so
the IMA of a screw is larger if the threads are
closer together.
Some examples of screws include the lid of
jars and bottles, cork screws, augers, and
even spiral stair cases.
Mr. Saoulis
- Wedge: simple machine that is an inclined plane with one or
two sloping sides.
Knives, scissors, axes, and sledge hammers are some
examples of a wedge.
- Compound machine: machine that is a combination of two or more simple machines.
Mr. Saoulis