Simple Machines

SPH4C

March 2010

History

• Archimedes – 3rd Century BC

• Heron of Alexandria – 10-75 AD

• Galileo Galilei – 1600 AD

What is a machine?

• Device that allows us to do work with less effort.

• Work is done when a force moves an object in the direction of that force.

Work

• Work is the energy transferred to an object.

• Machines make work easier.

• W is the work done on the object,• F is the magnitude of the force,• Δd is the magnitude of the displacement.

dFW

Machines

• Machines are designed to achieve at least one of five main functions:– Change energy from one form into another– Transfer forces– Change the direction of a force– Change the magnitude of a force– Change distance or speed

Simple Machine Families

• Lever Family– Lever– Pulley– Wheel and axle– Gears

• Inclined Plane Family– Inclined plane– Wedge– Screw

Lever

A lever is a rigid bar that can rotate freely around a fulcrum ( a support around which a lever can rotate).

An effort force, FE, is a force applied to one part of a lever to move a load at another part; the load exerts a load force, FL.

Lever Classes

• First-class– Fulcrum between FE and

FL

• Second-class– FL between FE and fulcrum

• Third-class– FE between FL and fulcrum

Other Levers

Inclined Planes

• An inclined plane is a ramp that increases the load than can be moved by an effort force.

Inclined Planes

• A wedge is a double inclined plane that increases the applied or effort force.

• A screw is an inclined plane wrapped around a central shaft that increases the applied or effort force.

Compound Machines

• A machine made of two or more simple machines.