Simple Machines

Supporting files for this material can be found here.

  • Energy is the ability to do work.

Work is the use of a force to move an object across a distance.  The formula for work is:    work = force x distance

A force is any push or pull on an object.  Force is measured in units called Newtons (N).  It takes 1N to move a mass of 100g.  The formula for force is:    force = mass x acceleration

Work is measured in units called Joules (J).  Using our formula for work, we know that 1 Joule is equal to 1 Newton times 1 meter.  (1J = 1N x 1m)

Types of Energy
Potential Energy - "Stored energy" or "Energy of Position".  This is energy that is stored by the object's position, shape, or chemistry.

Kinetic Energy - "Energy of Motion".  This is the energy that an object has while it is moving.

Chemical Energy - A type of potential energy that is stored in chemicals (food, fuel, etc.) and is realeased by chemical reactions.  For example, when you eat food, your body digests it to release the energy stored in the food so that you can run and jump and skip and play.

The Law of Conservation of Energy
Energy cannot be created or destroyed; it can only change form.

Types of Forces
  • Buoyancy - Force exerted when water pushes an object to its surface.  (i.e. - A ship's buoyancy causes it to float.)
  • Elastic Force - Exerted when an object wants to return to its original shape.  (i.e. - A stretched rubber band exerts an elastic force, because it will snap back to its original shape.)
  • Friction - Force that opposes motion.
  • Gravity - The pull exerted by the Earth.
  • Magnetism - Force exerted by a magnet (attractive or repulsive).
  • Mechanical Force - A physical push/pull exerted by an object.  (i.e. - Throwing the ball is an example of a mechanical force.)Pressure - Force created when a substance is compressed.  (i.e. - There is pressure at the bottom of the ocean from the weight of all that water pushing down.)

Simple Machines
  • Machine - A device that makes doing work easier.
  • Simple Machine - One of six basic devices that change the size or direction of a force.  Simple machines are divided into two categories:
    • Inclined Planes - Sloping surfaces (such as a ramp).
      1. Inclined Plane
      2. Wedge
      3. Screw
    • Levers - A bar that can pivot around a fixed point.
      1. Lever
        • 1st Class - fulcrum in the middle  (reduces input force, increases input distance - makes the work easier)
        • 2nd Class - resistance in the middle  (reduces input force, increases input distance - makes the work easier)
        • 3rd Class - effort in the middle  (reduces input distance, increases input force - makes the work faster)
      2. Pulley
      3. Wheel & Axle

We will be looking at four types of simple machines in this unit: the inclined plane, lever, pulley, and wheel & axle.  Students will need to learn and be able to use the following formulas:

1 N = 100 g                         10 N = 1,000 g = 1 kg

Work = Force x Distance     (J = N x m)

Mechanical Advantage =
Force Output
                                            Force Input

Efficiency = Work Output
                      Work Input

Input is the force/work that you put into a machine.  It is the work you do to push on the lever or pull the string of the pulley.

Output is the force/work that you get out of the machine.  It is the work that the machine does to move the object.

Mechanical Advantage is a measure of how much the machine multiplies your force.  For example, if a machine has a mechanical advantage of 3, this means that it will triple the force that you exert on it.  (If I push on the lever with 1N of force, the other end of the lever will push on the object with 3N of force.)  This number will generally be larger than 1.

Efficiency is a measure of how much work you get out of a machine, compared to how much you put in.  Efficiency is sometimes written as a decimal, and sometimes as a percentage.  As a general rule, it will always be less than 100% (less than 1, if written as a decimal).


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  • Supporting files for this material can be found here.

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