HOTS Science Primary 6 Interactions

Two identical balls are dropped from the same height. One is dropped into a tank of water, and the other is dropped through the air. Which of the following is correct about the forces acting on them as they fall?

A Gravity and air/water resistance act on both balls, but water resistance is greater.
B There are no forces acting on the ball in the air.
C Only gravity acts on both balls.
D Gravity acts more strongly on the ball in water.
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Worked Solution

Step 1: Gravity acts on both masses identically. Step [2-9]: Both move through a medium (air and water). Step [2-9]: Water is denser than air, so it exerts a much greater resistive force (friction/drag).

Correct answer: Gravity and air/water resistance act on both balls, but water resistance is greater.

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