A box is sliding across a table, and it gradually slows down and stops. Explain why it stopped, using Newton's Laws.

Question

xishem · Answer

Newton's 1st: An object in motion will stay in motion unless acted upon by an external force.

In this case, the object IS being acted upon by an external force: friction.

Newton's 2nd: The acceleration of an object is directly proportional to the net force acting upon it and inversely proportional to the mass of the object. In otherwords, F=ma

The object is accelerating because the frictional force between the box and the table is against the direction of motion of the box, therefore decelerating it since the net force is in the opposite direction of the velocity of the box.

I think that that's enough to describe the box's actions -- I don't think it's necessary to use Newton's 3rd, as it wouldn't add much towards explaining why the box stopped.

anonymous · Answer

Thank you, very helpful!! :D

.sam. · Answer

Include this,
$$F_{fr}+F_{R}>F$$
The frictional force with air resistance has to be greater than force of gravity parallel to surface

anonymous · Answer

ok, thank you very much!! :D