Simple Machines:

Objectives:

1.    Identify the six simple machines.

2.    Explain how each simple machine works

3.    Calculate the mechanical advantage for each simple machine.

Resources:

Notes:

Simple Machines:

There are six simple machines:

1. Inclined Plane

2. Wedge

3. Screw

4. Lever

5. Pulley

6. Wheel and axle

Inclined Plane:

An inclined plane is a slanted surface used to raise an object.  It reduces the force required to move an object by increasing the distance of movement.

• The MA of an inclined plane is the Length/Height

• The MA is always >1.  Why?

The height will always be shorter than the length. (dots.physics.orst.edu/.../ inclined_plane_orig.gif)

Wedges and Screws:

A wedge is simply an inclined plane that moves.

• A wedge multiplies a force from a larger area to smaller area. (think pressure)

• The longer and thinner a wedge is the less FE is required to overcome resistance.

A screw is an inclined plane wrapped around a cylinder.

• The screw multiplies the FE by acting through a longer distance. (em-ntserver.unl.edu/NEGAHBAN/ EM223/note16/IMG00006.GIF)

Lever:

A lever is a bar that is free to move about a pivot point when a FE is applied to it.

• The pivot point is called the fulcrum.

• There are 3 classes of levers

• The type of lever depends on the location of the fulcrum

1st class levers:

• The fulcrum is placed between the FE and FR

• 1st class levers multiply the FE and change its direction.

2nd Class levers:

• The FR is placed between the FE and fulcrum

• 2nd class levers multiply the FE but do not change its direction.

3rd Class levers:

• The FE is placed between the FR and fulcrum

•   3rd class levers multiply the distance but does not change its direction or increase its FE.

MA = FR/ FE or effort arm length / resistance arm length

• You should notice that the 3rd class lever will always have a mechanical advantage that is less than 1.

Pulleys:

A pulley is either a belt, chain, or rope around a wheel.

• A pulley can change the direction or the amount of a FE

A pulley attached to a wall or ceiling is a fixed pulley

• A fixed pulley cannot multiply FE, it can only change direction.

• Changing the direction makes lifting the object easier.

• The MA = 1

A movable pulley is hung on a rope so that it moves with the FE.

• A movable pulley can multiply the FE.

• A moveable pulley cannot change the direction of the FE.

• The MA > 1 The MA can be estimated by adding the lengths of rope below the top pulley.

Wheel and Axle:

• Is a lever that rotates in a circle.

• Is made of 2 wheels of different sizes.

• The FE is equal to the radius if the wheel.

• The FR is equal to the radius of the axle.

The MA = the radius of the wheel / radius of the axle Compound Machines:

Are a combination of 2 or more simple machines.

Cars, bikes, watch, … Nearly everything that we can think of is made from simple machines. How many simple machines can you see?