During a demonstration of Newton's laws of motion, a student used the
setup shown in Figure 1. The student flicked the index card with a
fingertip, and the coin fell straight down into a plastic cup as shown in
Figure 2.
Figure 1
Figure 2
Which of these best explains why the coin fell straight down into the cup
instead of remaining on the index card? TEKS 8.6(C)
A The coin was at rest until the card was removed, so it tended to
remain in the same location. Once the card was gone, the
unbalanced force of gravity caused the coin to fall.
B Moving the card applied an action force on the coin. Since the card
was gone, gravity applied a reaction force on the coin.
C The card had less mass than the coin, so a smaller force of gravity
acted on the card. The larger force of gravity on the coin made it
fall.
D The acceleration of the coin falling into the cup was equal and
opposite to the acceleration of the card.