Plan on incorporating this activity into a day at the beach. Check your local newspaper to determine the time that both low and high tide will occur. Arrive early for high tide to set up the experiment. Bring long wooden stakes and insert one into the beach at the edge of the water. Begin timing with a stopwatch. Insert a new stake every hour, as the tide moves back and record the time into a notebook. Record also the distance between each newly inserted stake. Once you have determined that the tide is low, end the experiment and clean up. Analyze the data at home, using the gathered notes to make calculations, such as how long each section of beach stays out of the water.
Use a casserole dish from the kitchen to help create your own tide. Place rocks and sand inside it before propping it up to make a sloping 'beach'. Put a few drops of food coloring into a tall glass of water and place it at the lowest end of the dish; the low tide zone. Insert a length of aquarium tubing into the glass and secure it with tape. Gently suck the tube to encourage water flow, then place it into the dish. Tape it secure. Raise the glass to siphon water into the dish, creating high tide. Lower the glass again to create a low tide.
Wash out an empty soda bottle, then fill it with three quarters of a cup of water. Use a few drops of food coloring to color the water. Add a half a cup of vegetable oil to the water and secure the cap. Separate the water and oil by rolling the bottle on its side; the oil will rise to the top of the mixture and the water will sink down. Make waves by tipping the bottle back and forth, observing their formation. Talk about wave formation at both low and high tides, questioning whether any differences would be expected.
Use a shallow pan to demonstrate how low and high tides work. Fill it about a third of the way with water and explain that each end of the pan represents a beach on the opposite side of the world. Explain that the moon's gravity pulls the ocean water away from the shore. Tilt the pan and explain that both the sun and the moon cause the earth to tilt. Observe how one "beach" is at low tide and the other "beach" is at high tide. Round out the activity by planning a trip to the beach where children will determine for themselves what is occurring with the tide.