When the index card is pulled away quickly from under the disk, several physical principles come into play, primarily inertia and the effects of gravity.
-
Inertia: According to Newton's First Law of Motion, an object in motion tends to stay in motion with the same velocity and in the same direction unless acted upon by a net external force. When the index card is pulled away, the disk does not have any horizontal force acting on it (since the card is withdrawn quickly and doesn't push the disk sideways). Consequently, the disk tends to maintain its state of motion, which is resting underneath the card.
-
Gravity: The only significant force acting downward on the disk is gravity. As soon as the card is pulled out, the disk is no longer supported by the card and will begin to fall under the influence of gravity.
-
Lack of Support: While the card is under the disk, it provides a support force that counteracts gravity, keeping the disk at rest. Once the card is removed, that support is gone, and gravity pulls the disk straight downward into the glass.
Thus, when you pull the index card swiftly, the disk remains in place momentarily because of inertia but then falls straight down due to gravity, ultimately landing in the glass. This demonstrates how inertia causes the disk to resist changes in motion, while gravity provides the force that pulls it down once the support is removed.
1 answer