Talk:Newton's laws of motion

figure skaters and 3rd law

hi, I wonder if the figure skater diagram is optimal? It doesn't indicate any forces: are they holding hands while spinning? are they (about) to push apart? Are there any forces at all involved?

Also, the key 3rd law concept is that of opposite laws: An ideal diagram would show one person pushing the other, and experiencing a force back into their body (the opposite reaction, and also the correct image for a free body diagram...

Removal

I removed the following as the conservation of energy article disproves it: Conservation of energy was discovered nearly two centuries after Newton's lifetime, the long delay occurring because of the difficulty in understanding the role of microscopic and invisible forms of energy such as heat and infra-red light.

Newton's unfaithful first law - better explained

There is the explanation:

The first law states that if the net force (the vector sum of all forces acting on an object) is zero, then the momentum of the object is constant. Momentum is mass times velocity, with the mass derived from density times volume, while velocity is an vector quantity which expresses both the object's speed and the direction of its motion; therefore, the statement that the object's momentum is constant is a statement that its mass, speed and the direction of its motion are constant.

The first law can subsequently be stated mathematically as

$\sum \mathbf {F} =0\;\Leftrightarrow \;{\frac {\mathrm {d} \mathbf {p} }{\mathrm {d} s}}=0.$

Consequently,

• An object that is at rest will stay at rest unless an external force acting upon it is strong enough to move the objects mass.
• An object that is in motion will not change its momentum unless it changes its mass or an external force acts upon it.

Cheers, 81.6.59.42 (talk) 13:08, 22 June 2015 (UTC)

Videos on page

In light of MIT removing the videos of Professor Lewin from the OCW site, the links don't work, and this page would do well to remove them, or link to other locations on the web where these videos may reside.

As the removal from the MIT website prompted an investigation into the nature of the 'serious matter' described, I learned of things not related to physics.

Thank you, CLK — Preceding unsigned comment added by 205.166.161.61 (talk) 19:52, 1 October 2015 (UTC)

Limitation

The limitations section does not say whether Newton's laws are applicable to cases where acceleration is measured relative to a rotating frame of reference. g4oep