I was pulling a trolley with lots of goods on it, it weighed nearly 150Kg I guess. When I applied the force to pull it, it was so hard at the beginning but was super easy to pull it when it started rolling. At the middle of my journey, I figured out that its even hard to stop. Simple school physics!, the static friction is higher than the kinetic friction. That's true! But is that the real reason for what I experienced. Who is the superstar here? what plays the big role? is it the friction or inertia? My idea is that's inertia since the motion of a huge train powered by a single engine could also be explained in terms of inertia. Can anyone explain?
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$\begingroup$ Does the trolley have wheels? Then you can (ideally) rule friction out. $\endgroup$– SteevenCommented Oct 18, 2016 at 23:08
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2 Answers
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It depends on where the mass is. In space there would be no friction with only inertia to overcome. On a flat surface here on earth there could be anything from almost 0% to 100% friction depending on the surface.
answered Oct 18, 2016 at 23:05
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Inertia will not stop the acceleration of the trolley, so you could pull very weakly for a very long time and it would have the same result. Friction introduces a minimum force that must be overcome to begin that acceleration. Before it starts moving, no work has been done.
In the idealized situation, then, inertia is king, but friction is the bureaucrat telling you what must be the size of the onions in your tribute to the king. The total tribute, however, is the same.
In the real case, static friction does not disappear instantaneously. A friend of mine wrote his PhD on the subject. It will require some work into deformation. So the bureaucrat takes his small due.
