A screw is a cylinder or cone shape with a spiral groove cut into it. The groove in a screw is called the thread. The thread helps the screw turn and go down into wood or some other object. Each time the screw is turned, the thread slides down a little more into the wood. The thread of the screw is actually an inclined plane, because it is a tiny ramp that goes from one end of the screw to the other.
Picture taken by Bailey
Soda bottles have screw caps. If you look inside the cap, you will see the thread. Jars have screw caps, too. These screws help the contents of the bottles and jars stay fresh.
Picture by Bailey
A drill is a large kind of screw that is used to make holes in things. It has a larger thread than smaller screws have.
Picture of screws in a pencil sharpener by Bailey
Did you know that the propeller of an airplane is a screw? Instead of screwing through wood, the propeller screws through the air and pulls the airplane forward.
The propeller on a boat works the same way. It screws through the water to push the boat forward.
Do you have a water hose in your yard and a faucet attached to your house? The end of the faucet has a type of screw, and so does the hose. The two screws join together so that they hold tightly and no water leaks out.
To learn more about screws, visit this web site: http://www.factmonster.com/ce6/sci/A0844134.html
