Simple Machines

A device created to make work easier.

How do machines make work easier?

• Machines can multiply the input force.• Mechanical Advantage (Force out / Force in)• Machines change the direction of the input

force.• Machines can never multiply work done that

would violate the law of conservation of energy!

What are three types of simple machines?

• Lever– 1st Class– 2nd Class– 3rd Class

• Wheel and Axel– Pulley

• Inclined Plane– Fixed and moving

Lever Classes

First class lever: See Saw

• E-F-R• Changes the direction of the input force.• Mechanical Advantage is adjustable.• Fin x d (effort arm) = Fout x d (resistance arm)

Second Class: Wheel barrow

• E-R-F• Always has a mechanical advantage greater

than 1.• The Resistance will always move a smaller

distance than the effort.• Effort and resistance move in the same

direction.

Third Class: Baseball Bat

• F-E-R• Effort and motion are in the same direction.• Mechanical advantage is always less than 1• Generally increase the speed of the lever.

Pulley: Bicycle pedals

• Fixed pulleys change direction but have no mechanical advantage.

• Mobile pulleys increase mechanical advantage.• Each rope attached to the load supports an equal

percentage of the load.• Multiple pulleys can greatly increase mechanical

advantage.• As mechanical advantage increases so does

distance.

Count the ropes!

Inclined planes: Ramps

• The lower the angle generally the greater the mechanical advantage.

• Reducing friction is the key.• Mobile inclined plane. An axe or a knife.

Efficiency: Work out/ Wok in

• How much energy can you convert to useful work?

• Where does the energy go that is not converted into useful work?

• The 2nd Law of Thermodynamics.

What are the major sources of Energy lost for each of our machines?

• Lever:• Pulley:• Inclined plane:

What happens to these loses of energy as the mechanical advantage

increases?• Lever

• Pulleys

• Inclined planes

Is there ever a free lunch?

• What is the general relationship between mechanical advantage and efficiency?

• What implications does this have for our high energy use society?

• How does this relate to respiration, combustion and photosynthesis?

• Matter works in cycles? Does energy?