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MassachusettsPhysics

Module 3: Momentum and collisions

5 dot points across 5 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.

Why does an object moving in a circle need a force pointing inward, even when its speed is constant?

Explain that circular motion requires a net force directed toward the center (a centripetal force), and identify the real force providing it in everyday examples (MA STE Introductory Physics, Motion and Forces).
A standard-level answer on circular motion for the Massachusetts High School Introductory Physics MCAS: why an inward (centripetal) force is needed, that the object accelerates even at constant speed, and which real forces provide the centripetal force.
11 min answer →

How do elastic and inelastic collisions differ, and what happens to momentum and kinetic energy in each?

Distinguish elastic from inelastic collisions, explain that momentum is conserved in both while kinetic energy is conserved only in elastic collisions, and analyze recoil and explosion situations (MA STE Introductory Physics, Motion and Forces).
A standard-level answer on collisions and explosions for the Massachusetts High School Introductory Physics MCAS: elastic versus inelastic collisions, why momentum is always conserved but kinetic energy is not, and how recoil and explosions work.
12 min answer →

Why is the total momentum of a system unchanged when objects interact, and how is that used to predict their motion?

State the law of conservation of momentum and use it to calculate an unknown velocity after a collision when no external force acts (MA STE Introductory Physics, HS-PS2-2).
A standard-level answer on conservation of momentum for the Massachusetts High School Introductory Physics MCAS: why total momentum is conserved with no external force, how to set up the before-equals-after equation, and how to solve for an unknown velocity.
13 min answer →

How do safety devices like airbags and crumple zones use the physics of impulse to protect people in a crash?

Apply science and engineering ideas to explain how a device that extends the time of a collision reduces the force on an object, and evaluate a safety design (MA STE Introductory Physics, HS-PS2-3).
A standard-level answer on crash safety and engineering design for the Massachusetts High School Introductory Physics MCAS: how extending the collision time reduces force, how airbags and crumple zones work, and how to evaluate a safety design under HS-PS2-3.
12 min answer →

How does the mass and velocity of an object combine into momentum, and how does a force over time change it?

Define momentum as p = mv, define impulse as a force acting over a time, and relate impulse to the change in momentum (MA STE Introductory Physics, Motion and Forces).
A standard-level answer on momentum and impulse for the Massachusetts High School Introductory Physics MCAS: momentum as mass times velocity, impulse as force times time, and how impulse changes an object's momentum.
12 min answer →