Mechanics is a core part of A-Level Physics. Revise the key concepts and common mistakes below, then lock them in with the free games.
Key concepts
MomentumProduct of mass and velocity: p = mv.
ImpulseChange in momentum: J = F·t = Δp.
ElasticCollision where kinetic energy is conserved.
InelasticCollision losing kinetic energy (often to heat).
Perfectly inelasticObjects stick together after collision.
ConservationTotal momentum before equals total after.
Newton's 1st LawBody stays at rest or constant velocity if F_net=0.
Newton's 2nd LawF_net = ma; force gives proportional acceleration.
Newton's 3rd LawEvery action has equal and opposite reaction.
WeightGravitational force on a mass: W = mg.
Normal forceContact force perpendicular to surface.
TensionPulling force transmitted through a string.
ScalarQuantity with magnitude only, no direction.
VectorQuantity with magnitude and direction.
Common mistakes to avoid
Questions where students often pick the tempting wrong answer — make sure you know the right one:
In a collision between two objects, what quantity is always conserved (in a closed system)?✗ Kinetic energy is always conserved in collisions because energy is conserved. ✓ Total momentum is always conserved; kinetic energy is only conserved in elastic collisions.
Why does a metal spoon in hot water heat up faster than a wooden one?✗ Metal heats up faster because it has a lower specific heat capacity, requiring less energy per degree. ✓ Metals have higher thermal conductivity, so heat is transferred more rapidly through them.
When energy is 'lost' as heat due to friction, what has really happened?✗ Energy has been used up and no longer exists. ✓ Energy has been transferred to the thermal store of the surroundings — it's not destroyed, just dissipated.
If an object is moving at constant velocity in a straight line, what is the net force on it?✗ There must be a forward force on the object to keep it moving. ✓ Zero — by Newton's first law, constant velocity requires zero net force.
When you push a wall, what does Newton's third law say about the wall?✗ The wall only pushes back if your force is strong enough to make it react. ✓ The wall exerts an equal and opposite force on you at the same instant.
Practise Mechanics — free games
Test yourself with these quick revision games for this topic:
See all 17 games in the Subjects Arcade →
More A-Level Physics topics
← All revision guides
Want to revise every topic this smart?
The Velvet Method teaches you to use AI to revise any subject — £25, lifetime access.
Explore the Course →