All machines are composed of simple machines. A simple machine is a device that changes the direction or magnitude of a force. Simple machines are devices that make the work required easier, or multiply it, causing more work to be done than normal. There are six (6) types of simple machines, listed below:
1. Lever- a lever is a movable bar which works against a fixed point called a fulcrum. Levers are useful for prying things, such as using a screwdriver to open a paint can lid.
2. Wheel and Axle- a wheel and axle is a basically a large circumference wheel surrounding and connected to a small circumference wheel. Think of a bicycle tire's outer rim and the axle it is connected to.
3. Pulley- pulleys are wheel and axle combinations that use a rope, chain, or a series of ropes/chains to both change the direction a force is applied and the magnitude of the force used.
4. Inclined Plane- an inclined plane is a fixed incline device that divides the height something is to be lifted (or lowered) over a linear distance, literally rise/run. A set of stairs is a good example of an inclined plane.
5. Wedge- a wedge is a double combination of inclined planes put together to deliver a "splitting" force; a wedge used to split firewood is a good example.
6. Screw- a screw is a combination of a wheel and axle and an inclined plane. Screws are used to increase the force used to hold something up or together, such as screws used in the construction industry.
For ideas about a model working machine, pick any machine in your house and examine it for examples of the six simple machines mentioned above. Decide what your machine will do and design the construction using any three of the simple machines listed here. Feel free to borrow what you observe with the machines in your home.