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Simple Machines
Ancient people invented simple machines that would help them overcome resistive forces and allow them to do the desired work against those forces.
Simple Machines
• The six simple machines are:
– Lever
– Wheel and Axle
– Pulley
– Inclined Plane
– Wedge
– Screw
Simple Machines
• A machine is a device that helps make work easier to perform by accomplishing one or more of the following functions: – transferring a force from one place to
another,
– changing the direction of a force,
– increasing the magnitude of a force, or
– increasing the distance or speed of a force.
Mechanical Advantage
• It is useful to think about a machine in terms of the input force (the force you apply) and the output force (force which is applied to the task).
• When a machine takes a small input force and increases the magnitude of the output force, a mechanical advantage has been produced.
Mechanical Advantage
• Mechanical advantage is the ratio of output force divided by input force. If the output force is bigger than the input force, a machine has a mechanical advantage greater than one.
• If a machine increases an input force of 10 pounds to an output force of 100 pounds, the machine has a mechanical advantage (MA) of 10.
• In machines that increase distance instead of force, the MA is the ratio of the output distance and input distance.
MA = output/input
Inclined Plane • The Egyptians used simple machines to build the
pyramids. One method was to build a very long
incline out of dirt that rose upward to the top of the
pyramid very gently. The blocks of stone were
placed on large logs (another type of simple machine
- the wheel and axle) and pushed slowly up the long,
gentle inclined plane to the top of the pyramid.
Inclined Planes
• An inclined plane is a
flat surface that is
higher on one end
• Inclined planes make
the work of moving
things easier
The Lever
• A lever is a rigid bar that rotates around a fixed point called the fulcrum.
• The bar may be either straight or curved.
• In use, a lever has both an effort (or applied) force and a load (resistant force).
There are 3 Classes of Levers
• Depends on the location of 3 items:
1. Fulcrum – fixed point on a lever
2. Effort Arm – the part of the lever that exerts the effort force.
3. Resistance Arm – the part of the lever that exerts the resistance force.
EA
RA
1st Class Lever
– Changes the
direction of the force
– Multiplies effort force
– Magnifies speed and
distance
– Ex: seesaw, crowbar,
scissors
2nd Class Lever
– Multiply effort force
– Mechanical advantage
is always greater than
1.
– Ex: bottle opener,
boat oars, wheel
barrow
3rd Class Lever
– Magnifies speed and
distance
– Mechanical Advantage
always less than 1
– Ex: baseball bat, golf
club, broom, shovel
WHEEL AND AXEL
• The axle is stuck
rigidly to a large
wheel. Fan blades
are attached to the
wheel. When the
axel turns, the fan
blades spin.
Pulleys
• Pulley are wheels and
axles with a groove
around the outside
• A pulley needs a
rope, chain or belt
around the groove to
make it do work
Diagrams of Pulleys
Fixed pulley: A fixed pulley changes the
direction of a force;
however, it does not create
a mechanical advantage.
Movable Pulley: The mechanical advantage
of a moveable pulley is
equal to the number of
ropes that support the
moveable pulley.
COMBINED PULLEY
• The effort needed to
lift the load is less
than half the weight of
the load.
• The main
disadvantage is it
travels a very long
distance.
Mechanical Advantage
• Ratio of Output Force to Input Force
• Follows simple pattern with Ropes
and Pulley system
Rube Goldberg Machines
• Rube Goldberg machines are
examples of complex machines.
• All complex machines are made
up of combinations of simple
machines.
• Rube Goldberg machines are
usually a complicated combination
of simple machines.
• By studying the components of
Rube Goldberg machines, we
learn more about simple machines