Machines:

Objectives:

    1.    Classify machines.

    2.    Define mechanical advantage and efficiency.

    3.    Calculate the mechanical advantage and efficiency of machines.

Resources:

    http://pc65.frontier.osrhe.edu/hs/science/pwork.htm

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 (F_E) – The amount of force that you put into the machine

• Resistance Force (F_R) – 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 (W_I) – The amount of work that is done on a machine

• W_I = F_E * d_E

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

• W_O = F_R * d_R

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

            W_I = W_O or F_E * d_{E =} F_R * d_R

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

 Mechanical Advantage:

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 = F_R/F_E  or MA = d_E/d_R

• 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 = W_O/W_I * 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.