Ball A solid, ball B dashed. Move the mouse (or your finger) over the graph to read values. Up is positive, so a falling ball has a
negative velocity. The gradient of y–t is v; the gradient of v–t is a.
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Object
Field
h / m
v₀ / m s⁻¹
Timing
t / s
t² / s²
Options
How to use this simulation
Choose the release heighth and the launch velocityv₀. With v₀ = 0 the ball is
dropped; positive v₀ throws it up, negative v₀ throws it down.
Set each value with ▼ and ▲ (hold to go faster; the ↑ ↓ keys or the mouse wheel in the box also work, Shift = ×10), or type a value in the box. ↺ puts it back to its start value. Outside the classroom range the box turns amber ⚠: fine to explore, but the lab can't do this.
Move the pointer over any graph (or tap it): a dashed line shows the values where it cuts each curve, or the values of the nearest data point.
Press ▶ Drop (or ▶ Throw). The strobe shows where the ball was every 0.1 s (less often for very long falls) — the gaps grow
because the ball speeds up. Slow ¼× plays the motion at a quarter of real speed (the times stay real).
Add ball B to drop two objects side by side. Switch air resistance on (Earth only) to see when mass matters.
Timing: the light gate gives the exact time; stopwatch adds a human reaction time (0.15–0.25 s) when
you start and when you stop, like the class experiment.
Press ● Record. The Data tab plots h against t² for the drops; gradient = g/2.
◂ 0.1 s / 0.1 s ▸ (or the ← → keys) step the motion back and forward and pause it, so you can discuss
each moment: the velocity and acceleration arrows stay on the screen. Graph tools: Area shades the area under
a velocity graph (= displacement) or an acceleration graph (= change in velocity) up to that moment and writes what the area is (its name and value) inside it; Tangent draws the
tangent there (gradient of a position graph = velocity, of a velocity graph = acceleration).
Work through the Tasks tab. Write explanations on your worksheet.
The physics
Up is positive. In a vacuum only the weight acts, so every object has a = −g (g = 9.81 m s⁻² on Earth),
whatever its mass.
s = ut + ½at² · v = u + at · v² = u² + 2as · s = ½(u + v)t
Dropped from rest through height h: h = ½gt², so t = √(2h/g) and
v = √(2gh).
Thrown up at u: top after t = u/g, max height above the hand = u²/(2g),
back at the hand after 2u/g.
With air resistance: Fd = ½ρCdAv² opposes the motion; the resultant is
smaller than W, so a light, large object falls more slowly.
Model: g = 9.81 (Earth), 1.62 (Moon), 3.71 (Mars) m s⁻²; air density 1.20 kg m⁻³. The balls are drawn bigger
than to scale. The Moon and Mars have no (or almost no) air, so air resistance is only available on Earth.
Newton's laws
The badge above the scene says which law applies at this moment: 1st law — at rest or moving at a constant velocity, the resultant force is zero (ΣF = 0); 2nd law — accelerating, ΣF = ma. The table under the free-body diagram adds up the forces (ΣF) and compares them with m a (▾ folds it). Tick 3rd-law pairs to see every force with its partner: the same size and type, in the opposite direction, acting on the other body (the Earth, the floor, the string, the fluid…).