A machine eases the load by either changing the magnitude or the direction of a force.  A machine DOES NOT change the amount of work done!

Warning:  this is pretty much the worst definition that I have ever seen, so read the definition of a simple machine quickly, then I will explain to make it easier to understand.  :)  A  simple machine is a machine that only contains one machine.  Explanation:  There are many simple machines, levers, pulleys, wheel and axle, gears, inclined planes, wedges, and screws.  A simple machine is any ONE TYPE of these machines.  If you have 10 pulleys that are connected together, you only have one simple machine because everything is a pulley.  If you have 10 pulleys and one lever connected together, you no longer have a simple machine, because you have two different types of simple machines that are linked together.  A compound machine consists of two or more different simple machines that are linked together.

In this type of machine, a wheel or spoke is locked to a central axle so that when one is turned, the other must turn.  A longer motion at the edge of the wheel is converted to a shorter more powerful motion at the axle.  This simple machine is a wheel and axle.  It is not just a wheel or just an axle.  One does not work without the other.

Watch the video to see a demonstration and my explanation of a wheel and axle.

A screw is a central core with a thread or groove wrapped around it to form a helix.  While turning, a screw converts a rotary motion into a forward or backwards motion.

I have included three short cartoon clips about various simple machines.  These videos are a great way to learn about the different simple machines and how the physics of machines relates to them. 

Some parts are kinda corny, but it makes the physics easy to understand!  Watch them!  This is a video about the screw and wheel and axle.

A single pulley simply reverses the direction of a force.  When two or more pulleys are connected together, they permit a heavy load to be lifted with less force.  The trade-off is that the end of the rope must move a greater distance than the load.

If you pull with less force, you will move a greater distance.  If you pull with more force, you will move a smaller distance.  The work will always be the same, you will just trade force for distance.

Watch this video to see the physics behind pulleys and how adding more pulleys can permit someone to use less force to move something.  Again, if you can pull with less force, you have to move a greater distance.  If you are pulling with more force, the distance that you move is less.  

A wedge converts motion in one direction into a splitting motion that acts at right angle to the blade.  Nearly all cutting machines use the wedge.  A lifting machine may use a wedge to get under a load.

If you are using a cutting tool, such as a knife, or axe, you are pushing down on the cutting tool (wedge), and the wedge is pushing the object that you are cutting to the left and the right.

The force that we are exerting by using the machine is called the input force and the force that the machine does is called the output force.  

Gears are toothed or pegged wheels meshed together to transmit motion and force.  

In any pairs of gears, the larger one will rotate more slowly than the smaller one, but the larger on rotates with a greater force.  Each gear in a series reverses the direction of rotation of the previous gear.

Watch my video to see gears in action and how using a smaller force results in a larger distance moved and a smaller distance moved results in a larger force.

A lever is a stiff rod that rotates around a pivot point.  Downward motion at one end results in upward motion at the other end.  Depending on where the pivot point is located, a lever can multiply either the force applied or the distance over which the force is applied.

A more scientific term for pivot point is fulcrum.  

Watch this video to see the physics behind levers.  Pay close attention to how they change the distance to accommodate different forces.

Rube Goldberg, was an American cartoonist, sculptor, author, engineer, and inventor.  Rube Goldberg is best known for his popular cartoons depicting complicated gadgets performing simple tasks in indirect, convoluted ways.  The cartoons led to the expression "Rube Goldberg machines" to describe similar gadgets and processes.  He is the inspiration for international competitions known as Rube Goldberg Machine Contests which challenge participants to create a complicated machine to perform a simple task.

Be sure to head over to google classroom and fill out the exit pass.