Speed
• Speed = distance ÷ time • s = d ÷ t • Units: m/s, km/h • Typical speeds: walking (1.5 m/s), running (3 m/s), car (13–30 m/s)
Distance–Time Graphs
• Gradient = speed • Flat line → stationary • Steeper line → faster • Curved line → accelerating/decelerating
Velocity & Displacement
• Speed = scalar, no direction • Velocity = vector, includes direction • Displacement = distance in a straight line from start to finish
Acceleration
• Acceleration = change in velocity ÷ time • a = Δv ÷ t • Units: m/s² • Positive = speeding up, negative = slowing down
Velocity–Time Graphs
• Gradient = acceleration • Flat line → constant velocity • Area under graph → distance travelled • Straight line up → uniform acceleration
Terminal Velocity
• When weight = air resistance • Resultant force = 0 • Object falls at constant velocity • Example: skydiver before opening parachute
Typical Values of Acceleration
• g = 9.8 m/s² (use 10 in GCSE) • Applies when no air resistance acts
Uniform Acceleration Equation (HT)
• v² – u² = 2as u = initial velocity v = final velocity a = acceleration s = distance
Stopping Distance (Intro)
• Thinking distance + Braking distance • Thinking distance = driver reaction time • Braking distance = how far car travels after brakes applied
Factors Affecting Thinking Distance
• Tiredness — slower reaction time • Alcohol or drugs — impaired judgement • Distractions — using a phone, talking, eating • Higher speed — distance travelled each second increases • Poor visibility (fog, night) — slower driver responses Thinking distance depends only on reaction time and speed.
Factors Affecting Braking Distance
Vehicle / road factors: • Worn brakes — less friction • Worn tyres — reduced grip, longer skid • Wet or icy roads — much less friction • Loose surfaces (gravel, dirt) Physics factors: • Higher speed — braking distance increases exponentially • Heavier vehicle — more force needed • Poor brake condition — less braking force Braking distance depends on speed, mass, road surface, and condition of brakes/tyres.
