Final answer:
When holding a cup of coffee, gravity exerts a downward force on the cup, while your hand exerts an upward force to hold it. These forces are action-reaction pairs according to Newton's third law, which means each force has an equal and opposite counterpart.
Step-by-step explanation:
When you're holding a cup of coffee in your hand, the forces at play include gravity and the normal force exerted by your hand. Specifically:
- Gravity pulls the cup downward with a force we will call the weight of the cup (w).
- Your hand exerts an upward normal force (Fhand) to counteract the weight of the cup due to gravity.
According to Newton's third law of motion, every action has an equal and opposite reaction. Therefore, the reaction to the cup's weight is the upward force supplied by the hand, and the reaction to the hand's force is the downward force that the cup exerts on the hand.