Question

A classroom demonstration of Newton's first law is as follows: A glass is covered with a plastic card and a coin is placed on the card. The card is given a quick strike and the coin falls in the glass. (a) Should the friction coefficient between the card and the coin be small or large? (b) Should the coin be light or heavy? (c) Why does the experiment fall if the card is gently pushed?

Answer 1

(a). The Coefficient of the Friction between the glass and the coin is very very small or either it should be zero, this is because if there will be very less or negligible friction then Coin will fall at exactly the same place as Newton's law will tell means, vertically below its point on card.

(b). Friction force on the coin = µmg

Acceleration of the coin =µmg/m =µg .

Acceleration is not dependent on mass, so it does not matter whether coin is light or heavy.

(c). The experiment will fall because the Static friction will oppose the Relative motion between the coin and the card. As a result instead of falling at center it goes with the Card and Newton's First law will not be verified.

Hope it helps.