There is tremendous energy both in moving air and in moving water. Moving air has been used for many purposes, e.g. in windmills for grinding corn, making electricity, etc. Moving water is used in hydro-electric power stations to make electricity. There is huge energy in the ocean – both in tides and waves – and much research is being done to see if the ocean can provide us with electricity. Trapped air and water can also produce great forces. Air brakes on buses and trucks, and drills for breaking up roads, are examples of pneumatics. Hydraulics (using trapped liquids) are used in many heavy machines because of their huge strength, e.g. bulldozers, forklifts, hydraulic brakes.