A-Level Physics · Topic 2
Mechanics: forces, energy and momentum: every key term you need (+ practice quiz)
16 flashcard terms for A-Level Physics Topic 2, written to match the course framework. Study them here, then drill them as interactive flashcards, or test yourself with the 8-question quiz — free, no account needed.
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Moment Force multiplied by perpendicular distance from the pivot. In equilibrium, clockwise moments equal anticlockwise moments.
Couple Two equal, opposite parallel forces not along the same line. Produces rotation with no resultant linear force.
Centre of mass The single point where the object's whole weight can be taken to act. An object topples once its line of action falls outside the base.
Projectile motion Horizontal and vertical motion are independent. Horizontal velocity stays constant; vertical motion accelerates at g.
Terminal velocity Reached when drag equals weight, so the resultant force and acceleration are zero and speed stays constant.
Newton's second law Resultant force equals rate of change of momentum. For constant mass this reduces to F = ma.
Newton's third law Forces occur in pairs of equal magnitude and opposite direction, acting on different bodies and always of the same type.
Impulse Force multiplied by the time it acts, equal to the change in momentum. Explains why crumple zones and airbags reduce injury.
Elastic vs inelastic collision Momentum is conserved in both. Kinetic energy is conserved only in an elastic collision.
Work done Force multiplied by distance moved in the direction of the force. No work is done when motion is perpendicular to the force.
Power Rate of energy transfer, equal to force times velocity for a constant force. Measured in watts.
Efficiency Useful output energy divided by total input energy. Always below one, because some energy is always dissipated.
Conservation of energy Energy cannot be created or destroyed, only transferred between stores. The basis of most mechanics problem-solving.
Hooke's law Extension is proportional to the force applied, up to the limit of proportionality. The gradient of a force-extension graph is the spring constant.
Elastic strain energy The area under a force-extension graph, equal to half the force times extension while the material obeys Hooke's law.
Free body diagram Shows every force acting on a single object and nothing else. The essential first step in almost any mechanics question.
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