CK-12 Physical Science Concepts - For Middle School

http://www.ck12.org Chapter 4. Motion and Forces

Mechanical Advantage of Different Types of Machines

Many machines—including inclined planes such as ramps—increase the strength of the force put into the machine
but decrease the distance over which the force is applied. Other machines increase the distance over which the force
is applied but decrease the strength of the force. Still other machines change the direction of the force, with or
without also increasing its strength or distance. Which way a machine works determines its mechanical advantage,
as shown in theTable4.2.

TABLE4.2:Mechanical Advantages

Strength of Force Distance Over which

Force is Applied

Mechanical Advantage Example

increases decreases >1 ramp

decreases increases <1 hammer

stays the same (changes

direction only)

stays the same =1 flagpole pulley

Summary

• The actual mechanical advantage of a machine reflects the increase or decrease in force achieved by the
  machine. It takes into account the force needed to overcome friction.


• The actual mechanical advantage can be calculated with the equation: Actual Mechanical Advantage=Output forceInput force


• The ideal mechanical advantage of a machine reflects the increase or decrease in force there would be without
  friction. It is always greater than the actual mechanical advantage because all machines must overcome
  friction.


• The ideal mechanical advantage can be calculated with the equation: Ideal Mechanical Advantage=Output DistanceInput Distance


• The mechanical advantage of a machine may be greater than, less than, or equal to 1, depending on the type
  of machine.

Vocabulary

• mechanical advantage: Number of times a machine multiplies the input force; calculated as the output force
  divided by the input force.

Explore More

Watch the video about mechanical advantage at the following URL, and then solve the problems below.

http://www.youtube.com/watch?v=K9RloG1rbNY

MEDIA

Click image to the left for use the URL below.

URL: http://www.ck12.org/flx/render/embeddedobject/82420

1. Juan uses a lever to lift a rock. He places the rock on the short arm of the lever and pushes down on the other
   arm of the lever. He applies 30 N of force over a distance of 1 m. The other end of the lever moves in the
   opposite direction and raises the rock a distance of 0.2 m. What is the weight (force) of the rock?