From Really Heavy to Really Light

You guessed it!  The inclined plane.

Picture a piece of wood.  That would be called a plane.  Leave it just on the floor and it's called a floor.  That is not an inclined plane.  If you raise one end up and leave the other end on the floor it's called a slide and it's also called a piece of wood that's lifted up.  That is an inclined plane.  If it's straight up and down then it's called a wall.  A wall is not an inclined plane. 

An inclined plane is a piece of wood that's on an angle.  Not a zero degrees angle.  Not a 360 degrees angle and not a 90 degrees angle. 

If you are using an inclined plane to lift stuff up and down it will weigh less than if you are picking it up with your hands.  The longer the inclined plane the less the stuff weighs.