Measure of how fast something is travelling, a scalar quantity with magnitude but no sense of direction
Velocity
A vector quantity with both magnitude and direction, can be positive or negative
If an object travels in one direction then eventually ends up back at the same point, its displacement is zero but distance travelled is not zero
Acceleration
The change in velocity per second (m/s^2)
Distance-time graphs
Gradient shows velocity, steeper gradient means faster speed, negative gradient indicates returning to starting point, horizontal line indicates stationary, curved line indicates changing velocity
Velocity-time graphs
Gradient shows acceleration, steeper gradient means greater acceleration, negative gradient indicates decelerating, horizontal line indicates constant speed
Calculating average acceleration or distance travelled from a velocity-time graph
Draw a straight line through the curved region and find its gradient to calculate average acceleration, calculate the area under the curve to find the distance travelled
Thinking distance
The distance travelled before the driver reacts
Braking distance
The distance travelled whilst the driver is reacting and braking
The overall stopping distance is the sum of the thinking distance and braking distance
Seatbelts
Strap you in and stretch slightly under large forces, increasing the distance moved for passengers to stop which decreases the magnitude of the deceleration, reducing the force experienced
Crumple zones
Softer areas at the front of the car which crumple upon impact, absorbing energy and increasing the time taken for the car to stop, reducing the deceleration and thus the force experienced by passengers
Airbags
Inflate automatically upon a crash, your head hits the bag and slows down, increasing the time taken for the head to stop moving and reducing the force on the neck
