Einstein's Box Change in Centre of Mass

In summary, the conversation is discussing the concept of compensation of shift in centre of mass. The question involves a box of mass M moving leftwards and a small mass m being added to the right end to prevent the centre of mass from moving left. The difference between the attempted solution and the given explanation is the choice of reference point - one being a fixed point in space and the other being the left end of the box. The question raises the question of whether to choose a reference point that is fixed in space or in the same frame of reference. A thought experiment is used to illustrate this concept, but it does not seem to apply in this particular scenario.
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Homework Statement



The question is posted here: http://galileo.phys.virginia.edu/classes/252/mass_and_energy.html

I'm not too convinced by their explanation of 'compensation of shift in centre of mass'

The Attempt at a Solution



What I understand is this:

1)Box of mass M moves distance d leftwards
2)To prevent centre of mass moving to the left, a small mass m is 'added' to the right endThen shouldn't it be:

M(d) = (L/2 - d)m

The difference between my answer and theirs is that:

I take the reference point to be an absolute, fixed point in space - the centre of the Box initially.
However, their reference point is the left-end of the box. But that has clearly moved a distance 'd' leftwards.
This raises the important question:

Do we 1)select a reference point that is fixed in space, unchanging with time OR 2) select a reference point in the same frame of reference (left end of the box in this case)

A simple thought experiment:

Imagine a box of length L, with its centre of mass initially at (0,0). Some time later the box moved 10 units right, with its centre of mass now at (10,0). Taking either (0,0) or left end of the box to be the reference point in this case would yield the same result..

However this doesn't seem to be the case in this experiment..
 

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any ideas?
 

FAQ: Einstein's Box Change in Centre of Mass

1. What is Einstein's Box Change in Centre of Mass?

Einstein's Box Change in Centre of Mass is a thought experiment proposed by Albert Einstein to demonstrate the principle of relativity. In this experiment, a person inside a sealed box throws a ball against one wall, causing the box to move in the opposite direction. This results in a change in the center of mass of the system.

2. Why is Einstein's Box Change in Centre of Mass important?

Einstein's Box Change in Centre of Mass is important because it illustrates the concept of conservation of momentum, which is a fundamental principle in physics. It also demonstrates the idea that the laws of physics are the same for all observers, regardless of their relative motion.

3. How does Einstein's Box Change in Centre of Mass relate to the theory of relativity?

Einstein's Box Change in Centre of Mass is a thought experiment that helps to explain the principle of relativity, which states that the laws of physics are the same for all observers, regardless of their relative motion. This experiment also demonstrates the concept of time dilation, where time appears to pass slower for an observer in motion compared to a stationary observer.

4. Can Einstein's Box Change in Centre of Mass be observed in real life?

No, Einstein's Box Change in Centre of Mass is a thought experiment and cannot be observed in real life. However, the principles demonstrated in this experiment have been confirmed through various experiments and observations in the field of physics.

5. What are some practical applications of Einstein's Box Change in Centre of Mass?

While Einstein's Box Change in Centre of Mass is a thought experiment, the principles it demonstrates have practical applications in various fields such as astrophysics, engineering, and space travel. For example, understanding the concept of conservation of momentum is essential for designing spacecraft and predicting the movement of celestial bodies.

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