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5. Forces

Forces and their interactions

5 lessons
5.1 Scalars and vectors The difference between scalar and vector quantities, with distance and displacement, speed and velocity, and mass and weight, and how vectors are drawn as arrows. AQA Edexcel OCR 5.2 Contact and non-contact forces Forces as interactions between pairs of objects, the difference between contact forces (friction, air resistance, tension, normal contact) and non-contact forces (gravity, magnetic, electrostatic). AQA Edexcel OCR 5.3 Weight, mass and gravity The difference between mass and weight, gravitational field strength, the equation W = mg, measuring weight with a newtonmeter, and the centre of mass. AQA Edexcel OCR 5.4 Resultant forces How to find the resultant of forces acting along a line, the difference between balanced and unbalanced forces, and how to draw free body diagrams. AQA Edexcel OCR 5.5 Resolving forces and vector diagrams Higher tier: using scale drawings to find the resultant of two forces at an angle, resolving a force into two components at right angles, and closed vector triangles for forces in equilibrium. Higher only AQA Edexcel OCR

Forces and elasticity

2 lessons
5.6 Stretching springs: Hooke's law Elastic and inelastic deformation, extension, Hooke's law F = ke, the limit of proportionality, linear and non-linear force-extension graphs, and energy stored in a stretched spring. AQA Edexcel OCR 5.7 Required practical: force and extension Required practical: investigate the relationship between force and extension for a spring, and use the results to find the spring constant and the energy stored. AQA Edexcel OCR

Moments and pressure

4 lessons
5.8 Moments, levers and gears Moments as the turning effect of a force, M = Fd, the principle of moments for balanced objects, and how levers and gears act as force multipliers. For Separate Science. Separate only AQA Edexcel OCR 5.9 Pressure Pressure as force per unit area, the equation p = F/A, and how the size of the contact area changes the pressure in everyday situations. For Separate Science. Separate only AQA Edexcel OCR 5.10 Pressure in liquids and upthrust Higher tier: how pressure in a liquid increases with depth and density, p = h rho g, and how the difference in pressure produces upthrust, floating and sinking. For Separate Science. Higher only Separate only AQA Edexcel OCR 5.11 Atmospheric pressure The atmosphere as a thin layer of air, how atmospheric pressure is caused by air molecules colliding with surfaces, and why it decreases with height. For Separate Science. Separate only AQA Edexcel OCR

Describing motion

3 lessons
5.12 Speed and velocity Speed and velocity, the equation distance = speed x time, typical speeds, average and instantaneous speed, and measuring speed with light gates. AQA Edexcel OCR 5.13 Distance-time graphs How to read and draw distance-time graphs, finding speed from the gradient, describing stationary and accelerating objects, and using a tangent to find the speed at a point. AQA Edexcel OCR 5.14 Acceleration and velocity-time graphs Acceleration as change in velocity per second, a = (v - u)/t, v^2 - u^2 = 2as, and finding acceleration and distance from velocity-time graphs. AQA Edexcel OCR

Newton's laws

5 lessons
5.15 Newton's first law and terminal velocity Newton's first law, inertia, and how falling objects reach terminal velocity when air resistance balances weight, including the velocity-time graph for a skydiver. AQA Edexcel OCR 5.16 Newton's second law Newton's second law F = ma, how acceleration depends on resultant force and mass, and inertial mass (Higher tier). AQA Edexcel OCR 5.17 Required practical: acceleration Required practical: investigate the effect of force and of mass on the acceleration of a trolley using a falling mass, light gates and a data logger. AQA Edexcel OCR 5.18 Newton's third law Newton's third law: pairs of equal and opposite forces that act on different objects, how to identify them, and why they do not cancel out. AQA Edexcel OCR 5.19 Circular motion Why an object moving in a circle at constant speed is accelerating, the centripetal force towards the centre, and what provides it in everyday examples. Edexcel OCR

Stopping distances

2 lessons
5.20 Stopping distance and reaction time Stopping distance as thinking distance plus braking distance, typical reaction times, factors that affect thinking distance, and how to measure reaction time with a ruler drop. AQA Edexcel OCR 5.21 Braking distance and large decelerations Factors that affect braking distance, why braking distance rises with the square of speed, the energy transfers in braking, and the dangers of large decelerations. AQA Edexcel OCR

Momentum

2 lessons
5.22 Momentum and its conservation Higher tier: momentum as mass times velocity, the principle of conservation of momentum in collisions and explosions, and how to use it in calculations. Higher only AQA Edexcel OCR 5.23 Changes in momentum and car safety Higher tier: force as the rate of change of momentum, F = change in momentum / time, and how crumple zones, seat belts, airbags and helmets reduce the force in a collision. Higher only AQA Edexcel OCR