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When I throw a ball at a wall and it bounces off of it and there is conservation of momentum we can say that the springiness of the ball and the wall is the action reaction force responsible for the conservation of momentum but if we zoom in at the atomic or subatomic scale at the interface of interaction what is specifically the first action reaction force that contributes to the ball bouncing off of the wall?

How did Rutherford rule any other forces out in order to conclude that the deflection of the alpha particle was due to electrostatic repulsion in his gold foil experiment?

Rutherford also shot electrons at a sheet of metal and they bounced back. What did the electrons interact with and what action reaction forced was responsible?

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  • $\begingroup$ en.wikipedia.org/wiki/Geiger%E2%80%93Marsden_experiments . "The prevailing theory of atomic structure at the time of Rutherford's experiments was the "plum pudding model"" , according to the plum pudding model " Both the negative and positive charges within the Thomson atom are spread out over the atom's entire volume, and Rutherford had calculated that this volume was too large for strong deflection to happen." etc $\endgroup$
    – anna v
    Commented Jan 9 at 19:30
  • $\begingroup$ There are two repulsive 'forces' in modern mainstream physics. One is electrostatic repulsion of like electrical charges. This force acts via 'interaction', i.e. the charges 'interchange' photons (both real and virtual), and momentum is conserved at every interaction. The other is the Pauli exclusion principle which says that two identical fermions cannot be in the same state. The PEP is a form of quantum entanglement and does not involve 'interaction'. It causes degeneracy pressure that resists compression. Rutherford couldn't have known anything about it. $\endgroup$
    – Chad K
    Commented Jan 9 at 19:30
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    $\begingroup$ The problem of the alpha particles bouncing off the Gold nuclei is essentially a problem of scattering off a central inverse square potential. The "Rutherford" formula quantifies the cross section for this type of interaction. $\endgroup$ Commented Jan 9 at 19:33
  • $\begingroup$ I guess I should add that the Heisenberg uncertainty principle is also a kind of 'resistive force' to confinement. A particle can't be in a fixed position with zero momentum. If you try to confine a particle to a small space, it gets a large momentum trying to escape the confinement. $\endgroup$
    – Chad K
    Commented Jan 9 at 20:00

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If we zoom in at the atomic or subatomic scale at the interface of interaction what is specifically the first action reaction force that contributes to the ball bouncing off of the wall?

Molecules at the surface of the ball and molecules at the surface of the wall are repelled from one another by electrostatic forces. This repulsion stretches the bonds between the molecules in the wall and in the ball, and deforms them. The bonds between molecules in the wall are very strong, so they only deform by a very small amount. The bonds between molecules in the ball are weaker, so they deform by a larger amount.

How did Rutherford rule any other forces out in order to conclude that the deflection of the alpha particle was due to electrostatic repulsion in his gold foil experiment?

The only force known to Rutherford was electrostatic repulsion (we can rule out gravity because it is not significant at atomic scales). The strong and weak forces were not discovered at the time - but even if Rutherford had known about them, they would have been unlikely to be involved in an interaction that did not disrupt the nuclei of the gold atoms.

What did the electrons interact with and what action reaction forced was responsible?

If there was no nuclear reactions involved then the electrons must have interacted with the orbital electrons in the target atoms, and been repelled by electrostatic forces.

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