2.1 physics

• Speed


  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