Gravitational & Inertial Mass: Why the Difference?

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Discussion Overview

The discussion revolves around the distinction between gravitational mass and inertial mass, exploring whether they are equivalent and the implications of their relationship in classical physics and relativity. Participants raise questions about their definitions, interactions, and the effects of acceleration on these types of mass.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants question why gravitational mass and inertial mass are treated as distinct concepts, suggesting they may be equivalent.
  • Others argue that the equality of gravitational and inertial mass in classical physics requires explanation, indicating a lack of apparent reason for their equivalence.
  • A participant expresses a personal belief that gravitational mass results from inertial mass, seeking validation for this view.
  • There is a discussion about the forces acting on train cars moving at constant velocity, with one participant pondering the implications of Newton's Laws in this context.
  • One participant suggests that acceleration affects inertial mass but not gravitational mass, indicating uncertainty about how these concepts interact.
  • Another participant brings up the equivalence of inertial and gravitational mass in the context of relativity, questioning whether acceleration increases the gravitational field of an object.
  • A later reply references Einstein's "Principle of Equivalence" and its significance in General Relativity, providing links to external resources for further reading.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the relationship between gravitational and inertial mass, with multiple competing views and uncertainties expressed throughout the discussion.

Contextual Notes

Participants express various assumptions about the nature of mass and its behavior under different conditions, including acceleration and interactions between charged and uncharged objects. There are unresolved questions regarding the implications of these assumptions on the equivalence of mass types.

JasonRox
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Why do we make such a careful distinction between gravitational mass and inertial mass, rather that talking about one mass only, since they are equivalent?
 
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There is no apparent reason why they should be equal in classical physics. The fact that they are equal requires explanation.
 
This is a question in the book. Practice question so it's not worth marks. I personally thought they are different, and that gravitational mass is a direct result from inertial mass.

Is that right?

Another question... I've been pondering this one.

Let's say we have they train cars. They say that the first couplings have more force exerted on them than the last one.

If they are moving at a constant velocity, and we ignore friction, would they have all equal forces of 0.

According to Newton's Laws, they will continue on forever. If one had to snap, which is impossible, it would be impossible to predict on top of that.
 
I could be wrong about this, but I am under the impression that acceleration does not increase gravitational mass of the object, only it's inertial mass.
 
Think about a collsion between two charged objects compared to a collison between two objects with no charge.

Pallidin in relativity the inertial mass and the gravitational mass are one in the same.
 
jcsd said:
Think about a collsion between two charged objects compared to a collison between two objects with no charge.

Pallidin in relativity the inertial mass and the gravitational mass are one in the same.

So, the gravitational field coming from a given object is increased by acceleration? Thus, would a finely balanced, perimeter weighted gyroscope, having a rest weight of "x" actually weigh slightly more when accelerated?
 
The equivalence of inertial mass and gravitational mass is one form of Einstein's "Principle of Equivalence", which led to General Relativity.

Here's a nice discussion
http://www.pa.uky.edu/~cvj/as500_lec6/as500_lec6.html
http://instruct1.cit.cornell.edu/courses/astro101/lec24.htm
http://csep10.phys.utk.edu/astr162/lect/cosmology/equivalence.html

Here's a research group that tests the principle
http://www.npl.washington.edu/eotwash/index.html
 
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