Make a sundial. Mark which direction is north. Mark the shadow every hour. Can you use it to show time? more...
Make a compass. Find north. Turn the compass. Does the needle rotate? What happens if expose it to a magnet? more...
Make timers by filling bottles with salt, sand or water. Count how long it takes for bottles to empty. more...
Make a spring scale and use it to weigh your halloween candy. Swing it around and measure force. more...