12-2: Simple Machines
Monday, December 14, 2015
8:02 AM
Key Terms:
1. simple machine – one of the six basic types of machines, which are the basis for all other forms of
machines.
2. compound machine – a machine made of more than one simple machine
I. The Lever Family
i. All levers have a rigid arm that turns around a point called the fulcrum.
ii. Force is transferred from one part of the arm to another, which multiplies or redirects the
output force.
a. Levers are divided into three classes
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b. Pulleys are modified levers
i. The point in the middle of a pulley is like the fulcrum of a lever.
ii. The rest of the pulley acts like the rigid arm of a 1st class lever.
iii. Multiple pulleys are sometimes put together in a single unit called a block and tackle.
c. A wheel and axle is a lever or pulley connected to a shaft
i. A wheel and axle is made of a lever or pulley (the wheel) connected to a shaft (axle).
ii. When the wheel turns, the axle also turns.
iii. When a small input force is applied to a steering wheel, the force is multiplied to become a
large output force applied to the steering column.
iv. Screwdrivers and cranks are other common wheel-and-axle machines.
II. The Inclined Plane Family
a. Inclined planes multiply and redirect force
i. An inclined plane turns a small input force into a large output force by spreading the work
out over a large distance.
ii. Pushing something up a long, gradual ramp is easier than pushing something up a short,
steep ramp.
b. A wedge is a modified inclined plane
i. A wedge functions like two inclined planes back to back.
ii. Using a wedge is like pushing a ramp, instead of pushing an object up a ramp.
iii. A wedge turns a single downward force into two forces directed out to the sides.
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c. A screw is an inclined plane wrapped around a cylinder
i. Like pushing an object up a ramp, tightening a screw with gently sloping threads requires a
small force acting over a larger distance.
I. Compound Machines
a. A machine that combines two or more simple machines is called a compound machine.
Quiz:
List the two families of simple machines and the type of simple machines that belong to each family. Then
describe what a compound machine is.
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