Newton’s Balls: A lesson in Motion and Friction

By Benjamin Flanders

Newton’s balls are a display toy usually used to show the principle of conservation of energy. It consists of five balls hung by two strings each. The strings are attached to two parallel bars and the balls are spaced so that each ball when at rest hangs right to next to the other. Each touching the other by the slimmest margins. In order to show the principle of conservation of energy one pulls a number of balls away from the rest and drops them. A corresponding number of balls on the other side of the group of five will continue on the arc showed by the original balls that were dropped.

Unlike other balls that we know and love, friction is not a wanted attribute. The placement and the way the balls are suspended are important because they decrease the effects of friction. This is the reason they are hung by strings. The strings are an efficient way for the balls to move. Also the balls are small enough to be played with by one hand. If they were larger then the strings would have to be longer and the speed of the balls as they go through their arc would be great enough to be effected by wind resistance. Also for this reason the material of the balls are important.

Newton’s balls are made of steel. They would have to be steel or some other material that is very dense and heavy because the heavier the balls, the smaller the effects of wind resistance would seem in comparison to the energy of the ball. Also because of steel’s hardness it is a very good transmitter for energy. Newton’s balls have to be able to transmit energy from one ball to the next. If Newton’s balls were made of a more plastic material then they would absorb a lot of energy that should be coming out of them. Not only is the material of the balls important but placement is also.

Newton’s balls swing back and forth but never side to side. Looking down from the top you would notice that all the balls are in a perfect line. This creates a two dimensional plane in which the balls work. This has to be the case because if the balls weren’t in a line and just a millimeter off to one side, the balls would be pushed to the side creating a three dimensional movement. This movement takes a lot of energy that would otherwise be transmitted to the other balls.

Newton’s ball are great at transmitting. This transmission of energy is shown by the relative stillness of the middle balls and the action of the last ball. What happens is that the one ball that you pull up stores potential energy with respect with its position of rest. When you release the ball it gains kinetic energy from gravity and hits the second ball. The kinetic energy is transferred to the second ball, and since the balls are made of steel and transfers the energy well, the energy gets transferred to the next ball and so on and so forth until the energy gets to the last ball. Like the other balls the last ball gains the energy but unlike the like the other balls it doesn’t have another ball to transfer the energy to. So the last ball is pushed up and moved by that energy. I think.

You can also pull on more than one of Newton’s balls. Lets take two for instance. When you pull on two and drop them the same thing happens as when you only pull on one except the energy is twice as great. The energy gets transferred through the middle balls the exact same way as with one ball, the only difference is at the end. Remember that there is twice as much energy going through the balls and when the energy is transferred to the second to last ball that ball pushes on the last ball with twice as much force. Since that force is twice the amount needed to move the last ball, the last ball starts moving halfway through the energy transfer leaving half the original energy in the second to last ball. This is still the energy needed to move one ball so that ball also moves up. Well I am going over my allotted page and that is basically all I know or think I know.