Maybe This will help out:
Friction and weight are common experiences and taken for granted, but were not always understood. Aristotle believed that objects that contained the "element," earth, fell because Earth was at the center of the universe, and that was the natural order of things. We now know that weight, which is the force of gravity between objects, not only makes apples fall from trees, but keeps the Moon circling the Earth, and the Earth circling the sun. Without gravity to hold them in orbit, they would continue to move in a straight line until interfered with.
Aristotle also believed (and some students still believe) that the natural state of an object is to be at rest. That is, he believed unless a force was pushing an object, the object will slow down to a stop. This view overlooks friction, the force that resists the movement of surfaces sliding against each other. Friction causes most objects we see to come to rest. Unlike Aristotle, we know that there is nothing pushing planets along their orbit: since there is no friction to slow down planets, they will continue to move until interfered with.
A man tries to push a crate of 8kg across a rough surface. The static friction coefficient is 0.6 and the kinetic friction coefficient is 0.4. Calculate the friction force exerted on the crate if: a) a horizontal force of 45 N is exerted on the crate and b) a horizontal force of 60 N is exerted on the crate
2 answers
Ff = mu Fn = mu mg = .6*8*9.8
So 45 won't do it, but 60 will.
Once it's moving
Ff = mu mg = .4*8*9.8
F - Ff = ma, solve for a
So 45 won't do it, but 60 will.
Once it's moving
Ff = mu mg = .4*8*9.8
F - Ff = ma, solve for a
0 answers