Air Resistance & Friction

Activities to try

1. 1

   Growing resistance: drop and watch the arrows balance

   Why it works: Air resistance is not fixed: it grows with both speed and surface area, and always pushes back against the direction of motion. When it balances weight the object stops accelerating and falls at a steady speed (it keeps moving). Two shapes of the same weight are NOT slowed the same.

   1. Build a falling object and use a slider to change its surface area — flatten a ball into a flat sheet, or widen a parachute canopy.
   2. Drop it down a tall chute and watch the upward air-resistance arrow grow from nothing as the object speeds up.
   3. Keep watching until the upward arrow matches the downward weight arrow and the object stops speeding up, then falls at a steady speed.
   4. Widen the canopy and observe the arrows balancing sooner, at a lower speed (it floats gently); streamline it and observe the upward arrow growing more slowly, so the object reaches a much higher speed before the arrows balance (it plummets).
   5. Use a 'fair test' mode to drop two objects differing in exactly one variable (e.g. surface area) and read the cause straight off the race.
2. 2

   Fair-test investigation: same paper, flat vs crumpled

   Why it works: Because the flat sheet and the crumpled ball are identical paper with the same weight, gravity pulls equally; the flat sheet meets MORE air because of its larger surface area facing the air, so it falls slower. At a given speed, the size of the air resistance depends on surface area and shape, not on the object's weight.

   1. Predict first: drop a flat sheet of paper (held level, not edge-on) and the SAME sheet crumpled into a tight ball together from the same height — which lands first, and why? (Use two identical sheets, one flat and one crumpled, so both can be dropped at once.)
   2. State the prediction and reason aloud or in writing BEFORE dropping.
   3. Drop both and observe which lands first.
   4. Weigh both to confirm they are identical in mass, so weight cannot explain the difference.
   5. Repeat the drop several times and compare; extend to a big vs small parachute, taking repeat readings and recording fall times in a table.
3. 3

   Which way does it push? Direction and retrieval practice

   Why it works: Air resistance acts opposite to the direction of movement — upward on a falling object — and larger area gives more resistance and a slower fall. It is not 'wind' and does not act in all directions.

   1. Order a set of parachutes/shapes by their fall time.
   2. Answer which way air resistance pushes on a falling object — up, down, or sideways — and justify it.
   3. Use a slider to explore how changing surface area changes fall time, predicting before each change.
   4. Draw or complete a force diagram on a falling object showing weight down and air resistance opposing the motion (up for a falling object).