Pearson International A Level Physics Core Practical 9: Investigate force and change of momentum

This core practical is part of Pearson's practical-learning programme. The method below is one defensible implementation, not a confidential instruction sheet. Centres may adapt equipment while preserving the scientific purpose, controls, measurements and safety requirements.

Aim and scientific principle

Measure force-time or velocity data around an interaction and test impulse-momentum or momentum conservation for a defined system.

Begin by translating the title into a testable question. Identify what is deliberately changed, what is measured directly, what is calculated and what must remain controlled. Predict a relationship only after naming the mechanism. A prediction without a reason is weak; a reason without measurable variables cannot guide a practical design.

Apparatus and setup

Use dynamics trolleys or low-friction track, force sensor or motion sensors, video scale, balance and data logger. Select every measuring instrument by range and resolution, not by name alone. Draw a labelled scientific setup that shows the working geometry and exactly where readings are taken. Include a control or blank when it distinguishes the target effect from drift, contamination or background response.

Before collecting results, check zero readings, calibration, leaks, alignment or sterility as relevant. Record the instrument resolution beside the first raw-data table. If a digital device displays more digits than its underlying accuracy supports, do not treat every digit as equally certain.

Method

1. Measure masses and establish a horizontal low-friction track with calibrated sensors or video scale.
2. Record velocities immediately before and after the interaction, or log force at high sample rate.
3. Repeat over different initial conditions while keeping the interaction type controlled.
4. Compare impulse from force-time area with momentum change, or total momentum before and after.

Plan the analysis before starting. This reveals whether an additional measurement is needed for a derived quantity and prevents a completed experiment from lacking a mass, length, concentration, background or calibration value. A method should be detailed enough for another trained student to reproduce, while avoiding decorative steps that do not affect validity.

Variables and controls

• Independent variable: initial speed, mass or interaction condition.
• Dependent variable: force-time impulse and/or velocity change.