Another important element of the physics of waterskiing is the speed at which the boat tows you. The average speed needed for a 150-pound person is 20 to 25 miles per hour (32 to 40 kph). However, when skiers use one ski, the speed needs to increase because there's less surface for pressure to build up on in the water.
When you're being towed in a straight line behind a boat, the two main forces acting on you are the force of the tow rope, which is created by the forward movement of the boat, and the force of the water on the skis. If there's constant tension in the tow rope, you'll travel at the same speed as the boat.
When you move in a direction perpendicular to the boat across the wake, the wave created by the boat and its engine, a centripetal force also comes into play. A centripetal force happens when a body moves in a circular path around another object, based on the fact that some force is pulling the body toward the center object. For example, think about a satellite circling the Earth. In that case, the gravitational pull keeps the satellite moving in a circular path around Earth. With waterskiing, the rope keeps the water-skier traveling in a circular path around the boat. When an object moves on a curve, it accelerates. Hence, when a water-skier starts to move on a curve around the boat, he or she accelerates. When centripetal, water and boat forces act on you at once, you'll move faster than the tow boat. The diagram above displays these forces at work.
Now that you know the physical principles behind waterskiing, you'll learn about the basics of standing up on those skis.