Dynamics

You will be able to

• State that the resultant force on a body equals its rate of change of momentum, F = Δp / Δt.
• Determine the impulse, and so the change in momentum, from the area under a force–time graph.
• Explain why increasing the contact time reduces the force for the same change in momentum, and why a rebound increases the impulse.

You will be able to

• Describe how drag increases with speed, so that a falling object's acceleration decreases until it reaches terminal velocity.
• Calculate the terminal velocity from W = F_D (+ U), for drag kv² in air and Stokes's drag 6πηrv in a liquid.
• Interpret the velocity–time and acceleration–time graphs of an object falling with air resistance.

You will be able to

• Apply the principle of conservation of momentum to collisions in one dimension, taking account of direction.
• Distinguish elastic and inelastic collisions by whether the total kinetic energy is conserved.
• State that, for a perfectly elastic collision, the relative speed of approach equals the relative speed of separation.