MadSci Network: Physics

Subject: classical mechanics

Posted by Radu Grigore
Grade level: 10-12
School: highschool 'Gh. Sincai'
City: Bucharest State/Province: No state given.
Country: Romania
Area of science: Physics

I do not agree with my new physics teacher in some problems. Please tell me who 
is right.

1. I consider that the force to which Hooke's law refers is the restoring 
force opposed by the material. She tells us that this force refers to the
force applied on the body. Of course I know that for practical problems it is 
numerically the same thing.

2. I consider that the _static_ friction is ALWAYS equal and opposed to the force
applied on the object, and so if there is no tangential force applied on the 
object the friction force is 0. She tells us that the static friction is always
smaller than the dynamic one but we do and can not know exactly how big it is. 
She even tells us that a body can _stay_ more easily on earth than on ice. My 
opinion is that a body can _walk_ more easily on earth because the friction force
can better annihilate the effect of the normal force and weight.

3. Consider this case:
          | A |           We make thease notations:
     ---------------          F - a force applied horizontal on
     |      B      |              A body
     ---------------          Fba - Friction force on A
         Earth                Fab - Friction force on B
                              Ff - Friction between B and earth
                              Ma, Mb - the mass of the bodies

We write thease equations:

I think that a1 is the acceleration of A body in earth's referrence
system. She's sure that a1 is relativ to B body, not to earth.

Re: classical mechanics

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