Machines:

Objectives:

1.    Classify machines.

2.    Define mechanical advantage and efficiency.

3.    Calculate the mechanical advantage and efficiency of machines.

Resources:

Notes:

Machines:

A machine is a device that makes work easier.  A hammer, bicycle ramp,  and scissors are all examples of simple machines

• Machines make work easier by changing the size or direction of the applied force.
• Machines can make work easier by multiplying the applied force.

• Machines can make work easier by redirecting the applied force.

There are always 2 forces involved in machines.

• Effort Force (FE) – The amount of force that you put into the machine

• Resistance Force (FR) – The amount of force that is applied by the machine.

Since there are 2 types of forces, there are 2 types of work.

• Work Input (WI) – The amount of work that is done on a machine

• WI = FE * dE

• Work Output (WO) – The amount of work that is done by the machine.

• WO = FR * dR

Although machines can make work easier, they do not multiply work.

WI = WO or FE * dE = FR * dR

The work output can never be greater than the work input.

Mechanical advantage is equal to the number of times a machine multiplies the effort force.

• Is equal to the resistance divided by the effort force

• MA = FR/FE  or MA = dE/dR

• The MA can be less than 1, 0, or greater than 1

If the MA is > 1, the machine multiplies force.

If the MA is = 1, the machine changes the direction of the force.

If the MA is < 1, the machine increases the distance or speed of an object.

Efficiency:

Efficiency is the comparison of work output to work input.

• Efficiency is expressed as a percent.

• Efficiency = WO/WI * 100

• The efficiency can never be greater than 100%

What is the major reason that the work output would be less than the work input?

Friction:

The less friction a machine has, the higher its efficiency and work output.