Physics · Simulator 005
Put a block on a ramp. Tilt the slope and change the friction to see when static friction gives way, how fast the block then accelerates, and how the forces resolve along and across the surface.
On a slope at angle θ, gravity mg splits into two parts:
along the slope: mg·sin θ
into the slope: mg·cos θ = N (normal force)
Friction acts along the surface and opposes motion. While the block is at rest, static friction matches the pull up to a limit: f ≤ μs·N. The block starts to slide when tan θ > μs. Once sliding, kinetic friction is μk·N, and the acceleration down the slope is
a = g (sin θ − μk cos θ)
Mass cancels out of both the sliding condition and the acceleration.
The push control applies an extra force along the slope; positive pushes up the slope. With a push, the block may slide up or down.
Model: rigid block, Coulomb friction with constant coefficients, no air resistance. Real coefficients depend on surfaces and conditions.
A 5 kg crate rests on a 30° ramp with μs = 0.7. What friction force is acting on it right now? (Hint: it is not μs·N.)
The crate is not sliding (tan 30° = 0.577 < 0.7), so static friction only needs to balance the downhill pull: f = mg sin 30° = 5 × 9.81 × 0.5 = 24.5 N. The maximum available, μs·N = 0.7 × 42.5 = 29.7 N, is a limit, not the actual value. The readout shows both.