Forces and Motion covers the fundamental mechanics of Edexcel IGCSE Physics — from describing motion with graphs to explaining it with Newton\'s laws and conserving momentum in collisions.
Speed = distance / time (m/s). Velocity = displacement / time (includes direction). Acceleration = change in velocity / time (m/s²). Distance-time graphs: gradient = speed; horizontal = stationary; steeper = faster. Velocity-time graphs: gradient = acceleration; area under graph = distance; horizontal = constant velocity. Equations of motion: v = u + at, s = ut + ½at², v² = u² + 2as.
First law: an object stays at rest or constant velocity unless acted on by an unbalanced force. Second law: F = ma (resultant force = mass × acceleration). Third law: every action has an equal and opposite reaction (on a different object). Weight W = mg (g ≈ 10 m/s²). Momentum p = mv. Conservation: total momentum before = total momentum after (in a closed system). Impulse = force × time = change in momentum. Stopping distance = thinking distance + braking distance. Factors: speed, reaction time, road conditions, brake condition.
Speed is a scalar — it only has magnitude (how fast, in m/s). Velocity is a vector — it has both magnitude and direction. For example, "5 m/s" is a speed; "5 m/s due north" is a velocity. On distance-time graphs, the gradient gives speed. On displacement-time graphs, the gradient gives velocity. Average speed = total distance / total time, but average velocity = total displacement / total time. For circular motion, an object can have constant speed but changing velocity because the direction changes continuously.
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