A.2 Forces and momentumIB Physics SL: Flashcards

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State Newton's first law.

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State Newton's first law.: A body stays at rest or moves with constant velocity unless a resultant external force acts on it.
State Newton's second law in terms of momentum.: The resultant force equals the rate of change of momentum, F = Δp/Δt.
When must F = Δp/Δt be used instead of F = ma?: When the mass of the system changes (e.g. a rocket losing fuel).
State Newton's third law.: If A exerts a force on B, B exerts an equal and opposite force of the same type on A.
What is the rule for static friction?: Ff ≤ μsFN — it matches the applied force up to a maximum of μsFN.
What is the frictional force on a sliding body?: Ff = μdFN, where μd is the coefficient of dynamic friction.
State Hooke's law.: FH = −kx: the restoring force is proportional to the extension and opposite in direction.
Give the viscous drag on a small sphere.: Fd = 6πηrv.
What is the buoyancy force on a body in a fluid?: Fb = ρVg, the weight of fluid displaced (ρ = fluid density, V = volume displaced).
Define impulse.: J = FΔt, the average resultant force × contact time; equal to the change in momentum.
What is conserved in an elastic collision?: Both momentum and total kinetic energy.
In an explosion from rest, what happens to momentum and kinetic energy?: Total momentum stays zero; kinetic energy increases, supplied by stored energy.
Give three expressions for centripetal acceleration.: a = v²/r = ω²r = 4π²r/T².
Why is a body moving in a circle at constant speed accelerating?: Its direction, and so its velocity, is continuously changing; the acceleration is towards the centre.