# Mach's Principle and Newton's Pail Experiment?

• Deslaar
In summary, the water in a spinning pail is rotating relative to the "fixed stars", which means that the water is accelerating.
Deslaar
Can someone please explain this to me and the apparent mystery it's suppose to offer with regard to absolute acceleration.

I don't see it, a spinning pail of water that results in a curved surface is meant to somehow reveal an insight into relative mass and absolute acceleration. As far as I can tell, the curvature of the water is completely explained by classical mechanics.

What am I missing? Thanks.

Someone? Please? Am I being unclear?

Newtonian mechanics relies heavily on inertial frames of referance. Those are the frames of referance in which Newton's laws are supposed to hold. Mach observed that inertial frames were not rotating relative to the so-called "fixed stars". This gave rise to Mach's Principle which states that the inertial property of any given object depends on the presence and the distribution of other masses.

SO if you're accelerating with respect to an inertial frame of referance what that is supposed to mean, at least according to Mach's Principle, is that you're accelerating relative to the "fixed stars". so there is no "absolute acceleration". Only acceleration with respect to an inertial frame which in turn means that you're accelerating relative to the "fixed stars".

A spinning pail of water is thus rotating relative to the fixed stars. So if the water is trying to climb out of the pail, i.e. the surface of the water is curved, then you're (or actually the bucket) is rotating relative to the fixed stars.

Pete

Originally posted by Deslaar
Someone? Please? Am I being unclear?

Well, ..OK; but only because you're a friend of St. Thomas Aquinas.

Newton recognized constant motion is relative. However, rotation is different; and one can determine which party is actually rotating and which is stationary due to the principle of inertia.

If two bodies attached to a string appear to be rotating about each other with a string taut between them, then IF they are actually rotating then the string would have tension. If however it was the observer that was rotating around the two bodies, there would be no tension in the string.

Likewise, he reasoned with a pail of water. If you rotated around it, you would observe no curvature of water up the sides of the bucket; but if the water were actually rotating (and you were stationary) curvature would be observed. Thus, one could distinquish which party was actually rotating (WITHOUT reference to the outside environment)- and so he concluded rotational acceleration is not relative.

Creator

Opps I think I crossed Pmb's post.

Last edited:
Ahhh...thanks people.

## 1. What is Mach's Principle?

Mach's Principle is a concept proposed by physicist Ernst Mach that suggests that the inertia (the resistance to changes in motion) of an object is determined by the distribution of all the matter in the universe. In other words, the motion of an object is influenced by the mass and movement of all other objects in the universe.

## 2. How does Mach's Principle relate to Newton's Pail Experiment?

In Newton's Pail Experiment, a bucket filled with water is attached to a rope and swung in a circular motion. According to Mach's Principle, the water in the bucket would be affected by the inertia of all the matter in the universe, causing it to bulge outwards as the bucket is swung. This is because the water is not only affected by the forces acting on it locally, but also by the distribution of matter in the entire universe.

## 3. What is the significance of the Newton's Pail Experiment in understanding Mach's Principle?

The Newton's Pail Experiment was designed to demonstrate Mach's Principle and its application to rotational motion. By showing that the motion of the water in the bucket is affected by the matter in the entire universe, it provides evidence for Mach's Principle and helps us better understand the relationship between inertia and the distribution of matter in the universe.

## 4. Is Mach's Principle widely accepted in the scientific community?

Mach's Principle is a controversial concept and has been debated for many years. While some scientists believe it offers a deeper understanding of the laws of physics, others argue that it is difficult to test and may not be compatible with other theories, such as general relativity. Therefore, the acceptance of Mach's Principle varies among scientists and continues to be an ongoing topic of research and discussion.

## 5. Are there any practical applications of Mach's Principle?

At this time, there are no direct practical applications of Mach's Principle. However, it has influenced the development of other theories, such as the Einstein-Cartan theory, which attempts to incorporate Mach's Principle into general relativity. Additionally, understanding the relationship between inertia and the distribution of matter in the universe may have implications for our understanding of the origins and evolution of the universe.

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