Stopping Distances

Stopping distance

• Stopping distance $=$ thinking distance $+$ braking distance
  • Thinking distance: the distance travelled during the driver's reaction time
  • Braking distance: the distance travelled under the braking force
• For a given braking force, the greater the speed, the greater the stopping distance. Thinking distance is proportional to speed; braking distance is proportional to speed squared (it takes four times the distance to stop from twice the speed)
• Typical values: at 13 m/s (30 mph) about 9 m thinking + 14 m braking $= 23$ m; at 31 m/s (70 mph) about 21 m + 75 m $= 96$ m
• (Physics only) Estimate stopping distances over a range of speeds, and read graphs of speed against stopping distance for different vehicles