PSC 1121 Lecture Notes - Lecture 6: Kilogram, Net Force, Weightlessness
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Physical science (l6, l7, l8, l9) for(cid:272)es a(cid:374)d newto(cid:374)"s law"s/weight/free fall/weightless(cid:374)ess: a force is the push or pull on an object. It is the cause that makes object to change their state of motion (or their shape): frictional forces, due to the roughness of surfaces. When you hold a book between your hands, the force that holds it in place is friction. Isaac newton (1642-(cid:1005)7(cid:1006)7) e(cid:454)te(cid:374)ded galileo"s fi(cid:374)di(cid:374)gs a(cid:374)d realized how to use forces to understand motion: he was first a student and then a professor at cambridge university. N: a medium-sized apple weighs about 1 newton. Forces of everyday life (force inventory): weight: the force by which the earth pulls every massive object towards its center, normal forces: the forces between surfaces touching each other. They are normal to the surface and they are always present: friction: the forces between two surfaces trying to rub against each other.
