What it does
Free fall means falling with only gravity acting. Near Earth’s surface every freely falling object speeds up by 9.8 m/s each second, whatever its mass. This page drops a stone and a feather side by side so you can see that for yourself, then turns air on to show why a real feather behaves so differently. It is a teaching model with round numbers.
You can read the speed under each object as it falls and the landing times below. To see the same ideas on a sideways throw, try projectile launcher, and to plot the fall as a graph, open motion graphs live.
How to use it
- Leave “No air” selected and press Drop again.
- Change the drop height and watch the landing time.
- Switch to “With air” and drop again.
- Answer the quiz.
What each setting does
- No air / With air: with air, drag grows with speed. When drag equals weight, the speed stops rising. That speed is the terminal speed (50 m/s for the stone, 2 m/s for the feather here).
- Drop height: how far the objects fall. Higher means longer.
- Class 11: shows the formulas used when drag is included.
Worked example
With no air, after 1 s: v = gt = 9.8 × 1 = 9.8 m/s and s = ½gt² = ½ × 9.8 × 1² = 4.9 m. From 20 m, t = √(2 × 20 ÷ 9.8) = 2.02 s for both objects.
FAQs
Why do both land together without air? A heavier object has more weight, but also more inertia, so the acceleration is the same.
Why does a feather fall slowly in air? Air drag on it is large compared with its tiny weight, so it reaches terminal speed almost at once.
Is g exactly 9.8? It varies a little with place. 9.8 m/s² is the standard school value.
What is terminal speed? The steady speed reached when drag balances weight, so there is no more acceleration.
Where the numbers come from
- g = 9.8 m/s² (standard value used in school). Terminal speeds are made-up round teaching values. Drawings are fibub's own.
Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.
Last updated 2026-11-10.