Mass, inertia and linear momentum

Repair the common break

Common misconception: Mass and weight are interchangeable measures.

Correct model: Mass measures inertia; linear momentum is the vector product of mass and velocity.

Worked transfer

A 0.50 kg trolley moving at −3.0 m s⁻¹ has momentum −1.5 kg m s⁻¹. Its mass remains 0.50 kg; the sign belongs to velocity and momentum, not mass.

Guided practice

Explain why “Mass and weight are interchangeable measures.” fails. Then construct one example that correctly applies mass, inertia and linear momentum.

Independent practice

Compare the momenta of a 900 kg car moving east at 20 m s⁻¹ and a 1200 kg car moving west at 15 m s⁻¹ using east as positive.

Return to the recorded repair plan when the explanation and application are secure enough to re-test.