|MadSci Network: Physics|
with respect to your questions I must make some declarations. :
In the second question, in the one which takes issue with the friction$BCT(J force, you say that when there is no tangential force there is no friction$BCT(J force and this is not true, since there always exists a friction$BCT(J force due to (by Newton$BCT(J mechanics):
being : Uk =Static friction coefficient
Ff = Force of friction
Fn = Normal Force to the body. (perpendicular to the body).
Something which shows us that there is always a friction$BCT(J force, since in the worst case, this normal force will be a component of the weight.
The other thing with respect to walking on the land as opposed to ice is that the ice$BCT(J Uk is less than land$BCT(J Uk and so the applied friction$BCT(J force is greater on land in comparison with ice. With respect to the first question :
The force that Hook$BCT(J law refers to is to the force exercised by the body when an external force is applied to the body. This force is equal and opposited to the external force applied.
That is the reason why you can use it like the external force! With respect to the third question I consider :
The a1 acceleration is referenced to the body B and not to the land!
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