One of the first accomplishments of Archimedes, an ancient Greek mathematician, was his description of the lever. A lever can be made using a fulcrum, lever and some sort of load. Depending on the size desired, the lever can be anything long with a flat surface, such as a ruler or piece of lumber. The fulcrum can be any object that can be placed under the lever, such as a triangle-shaped wooden block or a large cardboard box. The load can be any item that will sit on the lever, such as a small wooden block or a brick. Move the position of the lever and load to demonstrate the amount of effort it takes to raise the load.
Students can discuss the invention of the battery while making a potato battery to demonstrate how batteries work. They will need a potato, a steel nail, a zinc-plated nail, 3 or 4 inches of copper wire with the insulation removed, a small piece of sandpaper and a basic voltmeter. Insert the copper wire and steel nail into the potato without letting them touch each other. Touch the ends of the meter leads to them and observe the reading on the voltmeter. Remove the wire and insert the zinc nail. Observe the reading. Remove the steel nail and insert the copper wire to observe this reading. Compare the results to reveal the best conductors.
Students can make a movie wheel, or phenakistoscope, and demonstrate to the class how movies were invented. Patterns for movie wheels can be found online at Sciencetoymaker.org. Choose a pattern such a rotating cube or a bounding cat. Print the pattern and retrace the lines to darken them if needed. Cut out the pattern. Insert a toothpick through the center. You may also glue a small foam cube to the back center of the pattern, and insert the toothpick through it. This helps the wheel turn more smoothly. Stand in front of a mirror and spin the wheel. Look through the notches and watch the wheel spin in the mirror to see the figures move.
Fourth-grade students can make a pinhole camera using an empty Pringles potato chip can. Take off the lid of the can and wipe out the inside. Measure about 2 inches from the bottom and draw a line around the can. Cut along the line. Poke a hole in the center of the metal bottom using a thumbtack. If the lid is clear, cover it with wax paper. Place the lid on the shorter section of the can. Tape two sections together. Cover the entire can with aluminum foil. Bright light works best so look out the window or go outside. Hold the tube to your eye and see an upside down picture of your view cast on the lid.