Screw
A screw actually uses an inclined plane to work! Look at the little ridges going around the screw. Imagine if you were to stretch them all out an unwind them. You would get a little ramp! When the screw is turned by a screwdriver, the inclined plane works on the material and drives the screw into the wood. Look at this video of a screw in action:
Can you see the inclined plane that is wrapper around the screw? Screws can either be turned by hand with a screwdriver or by a motor. A drill uses a motor to spin screws very fast and can screw together hard objects with no problem at all! We use screws all the time: to build buildings and make them safe, to hang up picture frames and televisions, and to hold two things together. Even plastic bottle lids use a screw to hold the lid on tight. Look here for some examples of screws:
Use the arrows to navigate through the simple machines or you can pick any one you want by clicking on the images above.