Acceleration
Accelerating does not mean going faster: it means the velocity changes, and braking or turning are accelerating too. It is measured in metres per second squared, which is not a notation quirk but metres per second gained every second. Gravity accelerates about ten each second, the same for a feather as for a stone with no air, as they checked on the Moon. And braking distance goes with the square of speed: at twice the speed you brake four times further, not twice.
Where this sits
- Comes after
- Motion
Exercises from this rung
Generated by the app, from easiest to hardest
You drop a stone. How fast is it going after 2 s?
Answer 20
Why It gains about 10 m/s every second, so after 2 s it is going 20 m/s. And a feather and a stone would fall the same with no air: they tested it on the Moon by dropping a hammer and a feather together, and both landed at once.
easierYou drop a stone. How fast is it going after 1 s?
Answer 10
Why It gains about 10 m/s every second, so after 1 s it is going 10 m/s. And a feather and a stone would fall the same with no air: they tested it on the Moon by dropping a hammer and a feather together, and both landed at once.
in betweenAt twice the speed, what happens to the braking distance?
- Four times as far
- Three times as far
- Twice as far
- The same
Why Four times as far, because the energy to get rid of goes with the square of the speed. It is the hardest fact to believe and the costliest: at 100 km/h you do not brake “a bit worse” than at 50, you brake four times further. Lgr22 names it explicitly under road safety.
harder