Would you be surprised to learn that Newton’s Cradle was invented in the 20th Century? How about that an actor created it in the 60s? The history of Newton’s Cradle began in Britain when actor Simon Prebble created the swinging-ball toy for the executive office. This wasn’t an easy sell for Prebble as toys were not an option for the desktop at the time. Eventually, he succeeded and convinced business people to buy, thus creating the executive toy market.
For the professional, Newton’s Cradle can be a personal representation of Isaac Newton’s third law of motion: For every action there is an equal and opposite reaction. Essentially, working toward a goal or vision, your internal drive and inertia move you forward toward success.
Although originally intended for office fun, relaxation and motivation, Newton’s Cradle was named in honor of scientist and mathematician Isaac Newton. The device demonstrates three physics principles: the laws of conservation of momentum, conservation of energy, and friction, in a simple and fun toy. This makes it a great tool for student interaction and learning, and because of this the toy has made it into the classroom.
Newton’s Cradles vary in size, weight and material, but mostly you will see them tabletop size with five small, same-sized silver balls evenly hanging, attached to two parallel horizontal bars that are attached to a base. Prebble’s Cradle had a wooden base; today you will find many high-quality, precision-made cradles, creating for an even more accurate demonstration of physics, and very appealing and sleek desktop toy.
Newton’s Cradle is used by holding up one of the balls and letting it release, swinging back toward the other four balls, this causes the ball on the opposite end to swing back the other direction, then fall again toward the other four balls. This continues until the two end balls become slower and slower, loosing speed, and finally stopping. So, how does this teach physics fundamentals?
Conservation of Energy
Newton’s Cradle demonstrates conservation of energy by beginning with the conversion of potential energy and kinetic energy. Potential energy is energy that results from something’s position. Kinetic energy is the energy something possesses because of its motion. Therefore, when we take the first ball of the cradle and rise it up, it is gaining potential energy, as we let go gravity will move the ball. As the ball falls and gets closer to hitting the second ball, its potential energy is going down and its kinetic energy is rising as the energy is converted.
At the ball’s lowest point its potential energy is zero, and because the law of conservation of energy states that energy cannot be created or destroyed, that potential energy converts into kinetic energy. The kinetic energy is displayed when the first ball hits the second ball, causing the energy from the first ball to continue and be transferred to the second ball. This continues down the line as the balls compress and convert their potential energy into kinetic energy so quickly that the balls don’t even seem to move, until ball four’s energy moves to ball five causing it to swing out. The fifth ball will move at the same speed and height as the first ball due to the conservation of energy, as it was hit with the same speed as ball one.
This sequence continues back and forth until the balls eventually stop. Why does this happen? In the classroom this is an opportunity to explain friction. It is impossible to have a perfect Newton’s Cradle where the energy continues to be converted, never ending because friction will eventually bring the balls to a stop.
The balls upon impact compress and return to their shape causing friction inside the balls, converting some of the kinetic energy into heat and vibration. This friction eventually causes the conversion of enough energy to cause the balls to stop moving.
Conservation of Momentum
Conservation of momentum answers the question, “Why doesn’t the first ball just bounce off the second upon impact and swing back again?” Momentum of the balls is directly correlated to the direction of motion, therefore if the motion begins moving to the right once you drop the first ball, the momentum will conserve and continue to move in that direction until reaching the final ball, switching the direction of motion with the force of gravity.
In a classroom, having a device that is clever and fun to help teach physics makes for an effective learning tool. Setting up experiments can help the learning process. Allow students to observe behavior, set expectations of results, predict what will happen if more than on ball is raised and released or even what would happen if the balls were not all the same weight.
There are many different ways to use and learn from a Newton’s Cradle, making it a diverse and creative tool enjoyed in classrooms throughout the world, as well as many office desks.
Bri Reagan is a writer and freelancer and wrote this article on behalf of Giant Newton’s Cradle.