Elementary Science Fair Proect with Matchbox and thread
Materials required:- an empty match box, a needle, broomsticks and thread.

Take an empty match box. Pull out the inner portion and make two small holes one on either side of it as shown in the figure. Take two broomsticks and insert them horizontally. Insert the thread through the top hole and pull it out through the bottom hole. Stitch across the small sticks tightly into lid so that the thread moves under one stick and over the other stick. See that the sticks do not slip down. Insert the inner lid into the outer one. Hold the thread vertically so that both the ends are tight. The box will rest somewhere on the thread when we slacken the pull. See how the box slides down. Tighten the thread between your fingers. See how it stops. You can order it to move or stop. It looks like a magic box obeying your commands.

What is the magic in thie science fair project? When the thread becomes loose the box slips down. When we hold it tight, the sticks press the thread firmly. The box does not move now.