What would I have to do to create a Newton's Cradle with the least friction that can maintain its momentum as long as possible? Find steel balls that are as elastic as possible. This will require that you buy a representative of as many types of steel ball as you can find, and bounce them off of a very hard surface to identify which steel ball has the highest coefficient of restitution. After that, try to eliminate all sources of "lost" energy, including sound, air drag, etc.
This will necessarily require that you find a way to use your Newton's cradle in a vacuum, which by itself will eliminate sound and air drag. Sign up to join this community.
The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Elasticity is the measure of a material's ability to deform and then return to its original shape without losing energy; very elastic materials lose little energy, inelastic materials lose more energy. A Newton's cradle will move for longer with balls made of a more elastic material. A good rule of thumb is that the better something bounces, the higher its elasticity.
Stainless steel is a common material for Newton's cradle balls because it's both highly elastic and relatively cheap. Other elastic metals like titanium would also work well, but are rather expensive.
It may not look like the balls in the cradle deform very much on impact. That's true -- they don't. A stainless steel ball may only compress by a few microns when it's hit by another ball, but the cradle still functions because steel rebounds without losing much energy.
The density of the balls should be the same to ensure that energy is transferred through them with as little interference as possible. Changing the density of a material will change the way energy is transferred through it. Consider the transmission of vibration through air and through steel; because steel is much denser than air, the vibration will carry farther through steel than it will through air, given that the same amount of energy is applied in the beginning. So, if a Newton's cradle ball is, for example, more dense on one side than the other, the energy it transfers out the less-dense side might be different from the energy it received on the more-dense side, with the difference lost to friction.
Other types of balls commonly used in Newton's cradles, particularly ones meant more for demonstration than display, are billiard balls and bowling balls , both of which are made of various types of very hard resins. Amorphous metals are a new kind of highly elastic alloy. During manufacturing, molten metal is cooled very quickly so it solidifies with its molecules in random alignment, rather than in crystals like normal metals.
This makes them stronger than crystalline metals, because there are no ready-made shear points. Amorphous metals would work very well in Newton's cradles, but they're currently very expensive to manufacture. The law of conservation of energy states that energy -- the ability to do work -- can't be created or destroyed. Energy can, however, change forms, which the Newton's Cradle takes advantage of -- particularly the conversion of potential energy to kinetic energy and vice versa.
Potential energy is energy objects have stored either by virtue of gravity or of their elasticity. Kinetic energy is energy objects have by being in motion. Let's number the balls one through five. When all five are at rest, each has zero potential energy because they cannot move down any further and zero kinetic energy because they aren't moving. When the first ball is lifted up and out, its kinetic energy remains zero, but its potential energy is greater, because gravity can make it fall.
After the ball is released, its potential energy is converted into kinetic energy during its fall because of the work gravity does on it.
When the ball has reached its lowest point, its potential energy is zero, and its kinetic energy is greater. Because energy can't be destroyed, the ball's greatest potential energy is equal to its greatest kinetic energy.
When Ball One hits Ball Two, it stops immediately, its kinetic and potential energy back to zero again. But the energy must go somewhere -- into Ball Two. Ball One's energy is transferred into Ball Two as potential energy as it compresses under the force of the impact. As Ball Two returns to its original shape, it converts its potential energy into kinetic energy again, transferring that energy into Ball Three by compressing it.
The ball essentially functions as a spring. This transfer of energy continues on down the line until it reaches Ball Five, the last in the line. When it returns to its original shape, it doesn't have another ball in line to compress.
Instead, its kinetic energy pushes on Ball Four, and so Ball Five swings out. Because of the conservation of energy, Ball Five will have the same amount of kinetic energy as Ball One, and so will swing out with the same speed that Ball One had when it hit. One falling ball imparts enough energy to move one other ball the same distance it fell at the same velocity it fell. What's going on there?
The balls deform elastically near the point of impact. Can you find any other hypothetical situations that would conserve energy and momentum but do not happen? If we can answer this question for the three-ball case we might gain insight into the N-ball general case. In fact, if we look carefully at the two-ball case we might learn something about how the elastic properties of the balls store and release energy.
Some textbooks and web sites tell you nothing other than a description of the behavior of the system and note that this behavior satisfies the conservation of energy and momentum. Perhaps they are "playing it safe" by not attempting to answer the obvious questions that "inquiring minds want to know.
Why is just one of many momentum and energy conserving outcomes selected by the laws of physics, to be the only outcome that happens? Ball 1 has initial speed v o , balls 2 and 3 are in contact at rest.
Case 3, all three balls emerge at different speeds. The successive impacts model. The simplest model to understand is one that invokes a "cheat". It assumes the N balls are initially not touching. The first ball is pulled back and strikes the second with speed. The first ball comes to rest and the second moves forward with speed V, hits the third ball, and so on down the line, till the last ball is ejected with speed V. This is valid when the balls are actually separated. But then some folks assume that the explanation is also valid when the balls are touching.
Well, the results are nearly the same in both cases, but the dynamics of the processes are certainly different. We will move on to look at the interesting case, where all balls are initially touching each other. The compression pulse model. This assumes that the balls are initially all touching.
A compression pulse begins in the metal balls at the point of first impact, traveling through the balls with the speed of sound. The speed of sound in the material of which the balls are made is much greater than the speeds of the balls. So the pulse "does its work" before any of the stationary balls have moved. The pulse travels forward and backward, reflecting from the ends of the string of balls and meeting again simultaneously at one point.
Where is that point? Well, if the pulse originated between the first two balls, the pulse meets between the last two balls, where it gives up its momentum and energy, giving the last ball a kick, and slowing the others to a stop before they have moved much. This sounds plausible at first, and it agrees with experiment.
But there's a troublesome issue. This model requires that a pulse of energy and momentum from the first ball ends up at one localized point, the point where the last two balls touch. How does it do that without dispersion, for the compression pulse initially goes in all directions within the balls, forward, backward, up, down and all directions in between?
It is reflected from the ball surfaces the balls are spherical after all in very complex paths and most of these paths are not equal in length from start to finish. Though it sounds good, it fails to convince the skeptical student. But the model does work remarkably well in predicting where the chain of balls will break first.
One seldom discussed confirmation test is this. The model predicts that the initial break point of the ball chain is determined by the length of the compression pulse paths through the chain, and not on the mass of the balls. Therefore if mass were added to one or more of the balls, without changing its diameter, the initial break point should be the same.
This can be done with the real apparatus by attaching weight to the bottom of one or more balls. Experiment confirms the prediction. The balls-and-springs model. This model imagines a linear string of balls with small springs between them. Newton's cradle fights air resistance and restitution efficiency of rebound. You then want the highest density, hardest balls with the highest restitution. Cobalt-sintered tungsten carbide is magnetic.
Polished hardened tool steel ball bearings are a good start. For more shallow wallets, tungsten steel, thoriated tungsten. Here are some possible reasons the cradle may not work as expected. Similarly, the frame may be not sufficiently rigid. Sign up to join this community. The best answers are voted up and rise to the top.
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