Choose the type at the top: 🧲 elastic (magnetic bumpers) · 🟠 inelastic (they bounce apart, some kinetic energy is lost) ·
🩹 stick together (Velcro) · 💥 explosion (a spring pushes them apart from rest).
Pick an example (class demo, slide problems, skaters, cannon) or set the masses and velocities yourself. Velocities have a sign:
+ is to the right. Type a value in the box next to a slider and press Enter.
Press ▶ Start. The contact plays in slow motion. ◂ / ▸ (or the ← → keys) step through it and pause.
The middle column shows the free-body diagrams of A and B during the contact — the two contact forces are a Newton's third law
pair: equal in size, opposite in direction, for the same time — and a bar chart of the momentum before and after.
Graphs: p–t shows that the total momentum stays the same. On F–t the Area tool gives the impulse on
each body (equal and opposite). KE–t shows what happens to the kinetic energy A.3 link.
● Record saves a trial; the Data tab plots momentum after against momentum before (and KE after against KE before).
Work through the Tasks tab. Write explanations on your worksheet.
The physics
p = mv · Σpbefore = Σpafter when no external resultant force acts (isolated system)
Why: during the contact FA on B = −FB on A for the same Δt, so the impulses are equal
and opposite: ΔpA = −ΔpB.
Stick together: mAuA + mBuB = (mA + mB)v.
Explosion from rest: 0 = mAvA + mBvB (recoil).
A.3 linkEk = ½mv² = p²/2m. Elastic: total KE the same before and after.
Inelastic: some KE becomes internal energy, sound…; perfectly inelastic (stick together): the largest possible loss.
Explosion: KE increases (from the spring's elastic energy, or chemical energy). Momentum is conserved in all of them.
Model: frictionless surface (no track: the bench is smooth enough over a short time). The bumpers act like a spring that
gives back a fraction of the relative speed (the "bounciness": 1 elastic, 0 stick together); the contact lasts about 0.1–0.2 s.
Explosion: a spring plunger releases over 0.1 s. Bodies are drawn the same size whatever their mass; the scale bar gives distances.