Dynamics: Newton's Laws, Momentum, Energy, Collisions, Friction

In the paper

Unit 1 carries 10 of the 50 physics marks; with eight chapters sharing them, this one averages a little over one (MEC publishes weights by unit, not by chapter). Dynamics is the widest chapter in the unit — four scope points where most chapters have one or two — and its ideas are the ones the rest of physics is built from. Momentum conservation reappears in nuclear recoil; the work–energy theorem is behind the electron-volt; friction sets the banking angle in circular motion.

The MEC scope line runs: Newton's laws and equilibrium conditions; force, impulse, momentum, torque, work, energy and power in linear motion; collisions; solid friction. The four headings below are those points, in MEC's order.

Three ways it comes:

• Recall — the statement of the third law, the unit of impulse, which of four forces is non-conservative, the relation between the angle of repose and the coefficient of friction.
• Understanding — why action and reaction never cancel each other, why a cricketer draws his hands back while catching, why the kinetic energy lost in a perfectly inelastic collision cannot be zero, why pulling a roller is easier than pushing it.
• Application — the tension in an Atwood machine, the reading of a weighing machine inside an accelerating lift, the common velocity after two bodies stick, the stopping distance of a braking car.