Choose an example at the top: 🛒 Smart Cart bouncing off a force sensor · 🥚 egg thrown into a sheet, a cushion or a wall ·
🎾 ball hit by a racket, a wall or a golf club.
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.
Choose the positive direction (→ right or ← left). Every velocity, momentum, force and impulse gets its sign from it.
Press ▶ Start. The contact plays in slow motion (the scene shows how much slower). ◂ / ▸ (or the ← → keys)
step through the contact and pause it.
The middle column shows the free-body diagram (forces to scale) and the momentum before and after. The orange arrow
Δp = pafter − pbefore is the impulse.
Graphs: on F–t, the Area tool gives the impulse J. On p–t, the Tangent
gives the gradient Δp/Δt = the force. Zoom on the contact shows only the collision (time in ms when it is short).
● Record saves a trial. The Data tab plots your trials and draws a best-fit line; its gradient is written next to it.
Work through the Tasks tab. Write explanations on your worksheet.
The physics
p = mv (kg m s⁻¹) · a vector: choose a positive direction
J = FΔt = Δp = mv − mu (N s = kg m s⁻¹)
Impulse = area under the force–time graph (any shape). Average force F = Δp/Δt.
Same Δp over a longer time ⇒ a smaller force: airbags, crumple zones, crash mats, bending your knees, the bedsheet.
A ball that bounces back has a larger Δp than one that stops: Δp = m(v − u) with u and v in opposite directions.
Model: the bumpers behave like springs that give back part of the energy (spring 80 %, magnetic 90 % of the speed; clay
almost nothing). Bumper data fitted to the class PASCO sample runs (0.500 kg cart at 0.62 m s⁻¹). Egg, ball and club: a smooth (half-sine)
or triangular force pulse lasting Δt. The egg cracks if the force goes above 25 N (a typical value). The weight is far too small
to matter during the short contact, so the motion is drawn along a horizontal line.
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…).