Choose an example at the top: 🪑 rotating chair · 🛰️ satellite · 🚗 car on a bend · 🎠 playground carousel.
Set the values with the sliders, or type a value in the box next to a slider and press Enter.
A value outside the allowed range is moved to the nearest limit (the box turns orange).
Press ▶ Start. The scene is a top view: the blue arrow is the velocity v (along the tangent), the orange
arrow is the acceleration a (towards the centre).
The middle column is the free-body diagram seen from the side, with only real forces (weight, normal force, friction,
tension or grip, gravity). The dashed orange arrow is their resultant: this resultant is the centripetal force
mv²/r. There is never an extra "centripetal force" arrow.
◂ / ▸ (or the ← → keys) step the motion and pause it. Graph tools: Tangent gives the gradient at
that moment (gradient of x–t = vx, of vx–t = ax);
Area shades the area under a velocity or acceleration graph up to that moment.
● Record saves a trial. The Data tab plots your trials and draws a best-fit line; its gradient is a physical
quantity (written next to the line).
Work through the Tasks tab. Write explanations on your worksheet.
The physics
T = 1/f · ω = 2π/T · v = 2πr/T = ωr
a = v²/r = ω²r (towards the centre) · F = mv²/r = mω²r
Satellite: gravity provides the force: GMm/r² = mv²/r ⇒ v = √(GM/r); the mass of the satellite cancels.
Car on a flat bend: static friction provides the force: μsmg ≥ mv²/r ⇒ vmax = √(μsgr); the mass cancels.
Rotating chair, beyond SL free spin: nothing turns the chair, so Iω stays the same
(angular momentum, HL topic A.4). Pull the arms in → smaller I → larger ω.
Model: G = 6.67 × 10⁻¹¹ N m² kg⁻², Earth mass 5.97 × 10²⁴ kg, radius 6.37 × 10⁶ m. Chair: body + chair
I = 2.0 kg m² (arms included), hands at 0.20 m when closed. Car: sliding friction μd = 0.8 μs.
Carousel radius 2.0 m. No air resistance.