Doing a simple machine science project is a great way to see how simple machines, when put together, form the basis of much of our modern world.
Put simply, a simple machine is a device that only requires a single force to do work. We are going to cover the basic ideas behind two of the most popular simple machines here: levers and pulleys.
Lets take an example: a lever. In this picture, the man is using a simple machine, a lever to lift a heavy rock he would not otherwise be able to move.
The simple machine pictured here is composed of the rod (lever) and fulcrum. The closer the fulcrum is to the object being moved, the easier it will be to move the object - that is, the closer the fulcrum is to the object being moved, the less force is required to move it.
A simple machine science project can be created using just this one concept - did you know that many common tools are based upon the lever? Crowbars, pliers, scissors and row boat oars are all based upon levers and fulcrums. Here is a great link about levers to help you with your simple machine science project.
Without going into the detailed physics behind how they work, pulleys allow a person to lift an object using about half the effort it would normally require.
What's going on here? Take a look at this diagram:
Lets say that the grey wheel in the center is a pulley, and the purple line is a rope - the grey weight-like object is, well, a weight - of 10 pounds. Now, if you were to try and lift the weight without the pulley in place, it would feel like you are lifting a 10 pound weight. No surprise.
But if you were to setup a pulley system like the one shown here - with one end of the rope attached to a fixed point, like a wall or a rigid beam, the pulley as shown with the weight attached to the pulley, then thread the rope through the pulley wheel - when you pull on the left side of the rope (the one with the arrow on the end of it) it would feel like you are lifting only 5 pounds, even though you are lifting 10!
Are we cheating somehow? How can you do half the work you normally would need to lift the weight using this simple machine science project? The answer is that we are not doing half the work. Even though the weight will feel lighter, we will have to pull twice as long to get the weight to the same height that we would get if we did not use the pulley system.
So, we are exchanging the force necessary to lift the weight for the distance or amount of pulling we need to do. No cheating involved.