If newtons third law (equal and opposite reactions) is correct, why does a newtons cradle work. ?

Question

Shouldn't the first ball bounce off the second with the same speed as the last balls reaction?

Answer 1

it does the second ball is at the other end as force transmits through the static balls , if you swing two balls then two balls swing at the other end .

Answer 2

Zebbedee is right, the opposite force of the second ball simply puts the first ball to rest.

To make the first ball bounce off the second ball right away, the second ball would have to apply more force than was applied by the first ball.

Answer 3

Newton's 3rd law always applies.

When the first ball strikes, it pushes ball 2. Ball 2 pushes back on ball 1 with an equal and opposite force.

The effect of ball 2 pushing ball 1 is to cause it to decelerate and come to rest.

The effect of ball 1 pushing ball 2 is to push the other balls until it hits ball 5. Here, as it is the only force *on ball 5*, ball 5 accelerates.

NB Ball 5 still exerts an equal and opposite force on ball 4! This force cancels the force placed on it by ball 3, keeping ball 4 in equilibrium.

Cheers,

Ben

Answer 4

First of all, Newtons third Law is the Law of reciprocal reaction: "All forces occur in pairs, and these two forces are equal in magnitude and opposite in direction."  So the question posted doesn't really question the third law. Maybe this is the common misconception about the third law.

The third law talks about a single force in which another force reacts on it. So meaning a ball with a force (bouncing in this case) is being reacted with an external force which can be the resistance of the floor when it bounces on.

To explain further, another good application is when you jump while standing on the floor. When you jump and land on the floor, the force you have exerted is equal to the force of the floor exerted on you. This is the reason why you can stand and won't be sinking on the soil.

Another example is when you sit on a chair. Wherein your weight which is also a force is equal to the force exerted by the chair wherein you do not stumble when you sit. That is also the reason why when your weight is greater than the force exerted by the chair, the chair usually breaks.

Answer 5

That executive toy was invented by Charlie Newton: nothing to do with Sir Isaac.

Answer 6

The energy is transmitted through the balls to the final ball, which is why that ball moves and the rest do not. The swings become less and less because of gravity, unless you have a battery in it to maintain the energy. Gravity in this case is an outside force (exerting a constant force downward on the balls). In a vacuum, the energy would be conserved.

Answer 7

"Every action has an equal and opposite reaction."

Third law

Whenever a particle A exerts a force on another particle B, B simultaneously exerts a force on A with the same magnitude in the opposite direction. The strong form of the law further postulates that these two forces act along the same line. This law is often simplified into the sentence "Every action has an equal and opposite reaction."

Answer 8

Make the set up simple, use two balls, as the first impacts the second it exerts a force on it causing an acceleration in the second at the same time the second exerts a reaction force on the first causing a deceleration (which brings it to rest) and the first swings upward with gravity exerting a force to slow it down and the process repeats. Now stick in a third ball. This first strikes the second resulting in a force which causes an acceleration into the third which results in a force on the third causing it to accelerate, It also causes a reactionary force on the first causing it to decelerate to rest. The third, under the influence of the force causes a reactionary force on the second causing it to decelerate. The acceleration and deceleration forces of the second cancel out and no change in motion is observed in an ideallized system. The system loses energy not to gravity but to friction and sound.

Answer 9

isn't this more about the conservation of energy?