Newton's Cradle: Speed of Force Q&A

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In summary, the conversation is discussing the speed of kinetic energy and its impact on a hypothetical scenario involving a Newton's cradle one light-year long. The participants mention that kinetic energy does not actually have a speed, but rather communicates force through pressure variations that travel at the speed of sound. This means that the ball at the far end of the cradle will not move until the pressure wave reaches it, which takes time. The conversation also touches on the concept of speed of sound and its relationship to the speed of light.
  • #1
The Divine Zephyr
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Hey I'm new here and I would like to propose a question about the speed of kinetic energy. If let's say we had a Newton's cradle one light-year long, will the last ball fly up as soon as the first ball hits the second? Assume all the balls are in perfect contact with each other. Does this happen instantly or at light or sub-light speed? I do not think the speed is limited, but what do you people think?

-tdz
 
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  • #2
Kinetic energy does have a "speed."

Futhermore, the balls communicate force via pressure. Pressure variations propagate at the speed of sound, which is different for different media, and is always less than the speed of light.

So no, the ball at the far end won't move until the pressure wave reaches it, which will take some time.

- Warren
 
  • #3
I think the the Newtons cradle example, the shockwave will travel through the material at the speed of sound (about 5-10 km/s).

Originally posted by chroot
Kinetic energy does have a "speed."
Don't you mean 'does not'?
 

FAQ: Newton's Cradle: Speed of Force Q&A

What is Newton's Cradle?

Newton's Cradle is a device that demonstrates the conservation of momentum and energy. It consists of a series of suspended steel balls that are able to swing back and forth like pendulums.

What is the purpose of Newton's Cradle?

The purpose of Newton's Cradle is to illustrate the principles of conservation of momentum and energy. It shows how energy and momentum can be transferred from one object to another without being lost.

How does Newton's Cradle work?

When one ball on the end is lifted and released, it gains potential energy as it moves upwards. This potential energy is then transferred to the next ball, causing it to swing upwards as well. This process continues until the energy is transferred to the last ball and it swings upwards. As the balls come back down, they transfer the energy back to each other, creating a continuous swinging motion.

What is the speed of force in Newton's Cradle?

The speed of force in Newton's Cradle is equal to the speed of the initial ball that is released. This is because the energy and momentum are transferred from one ball to the next without any loss. However, the speed of the balls may appear to decrease due to friction and air resistance.

What are some real-life applications of Newton's Cradle?

Newton's Cradle is mainly used as a teaching tool to demonstrate the principles of conservation of momentum and energy. However, it can also be used in some engineering and design applications, such as in shock-absorbing mechanisms or in the design of cranes and other lifting devices.

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