How it works
Acceleration is the rate of change of velocity — how many metres per second of speed an object gains (or loses) each second. A car doing 0–100 km/h in 6 seconds averages about 4.6 m/s², roughly half a g.
Negative acceleration (deceleration) is just acceleration pointing against the motion. Braking, catching a ball, and landing from a jump are all governed by the same relationship.
Expressing acceleration in g (multiples of Earth's gravity, 9.81 m/s²) makes it intuitive: 1 g is what you feel standing still; fighter pilots black out around 9 g; a hard car brake is about 1 g.
Use it in real life
Driving: comparing 0–100 km/h times between cars is really comparing average acceleration — this calculator converts marketing numbers into physics.
Sports: sprint coaches measure acceleration over the first 10 m because races are usually won by whoever changes velocity fastest, not by top speed.
Elevator comfort: passenger lifts are designed to stay under ~1.5 m/s² so the g-force change is barely perceptible.
Frequently asked questions
What's the difference between speed, velocity and acceleration?
Speed is how fast you move; velocity is speed with a direction; acceleration is how quickly velocity changes. You can accelerate without changing speed — turning at constant speed changes your direction, which is a change in velocity.
How do I convert 0–100 km/h times to acceleration?
100 km/h is 27.8 m/s. Divide by the time: a car doing 0–100 in 5 s averages 27.8 / 5 ≈ 5.6 m/s² (about 0.57 g).
What is 1 g of acceleration?
9.81 m/s² — the acceleration of free fall at Earth's surface. It's the natural benchmark for how strong an acceleration feels to a human body.