Acceleration measures how quickly velocity changes — the difference between the starting and finishing speed, spread over the time it took. That is the whole of a = (v − u)/t. Once you have it, the rest of the motion falls out of the SUVAT equations: the distance covered is just the average speed times the time, and dividing the acceleration by 9.81 gives the g-force, an intuitive way to feel how hard the change really is. A positive answer means speeding up; a negative one is braking.
Reviewed: June 19, 2026 · Author: Naveen P N, Founder — AI Calculator · Verified against: constant-acceleration kinematics (SUVAT).
The acceleration equations
These hold whenever the acceleration is constant. The distance can be found two ways that always agree: the average-velocity form (u + v)/2 × t needs only the speeds and time, while s = ut + ½at² uses the acceleration directly. The g-force conversion turns a bare m/s² figure into something tangible — 3 m/s² is a brisk but comfortable 0.31 g, whereas an emergency stop can briefly hit 1 g or more.
Worked example — a car pulling away
Scenario: A car accelerates from rest to 30 m/s (about 108 km/h) in 10 seconds.
The car accelerates at a steady 3 m/s² and covers 150 m reaching 30 m/s. Do it in half the time — 5 s — and the acceleration doubles to 6 m/s² (0.61 g) but the distance halves to 75 m, because the car spends less time at lower speeds. Slamming the brakes to stop from 30 m/s in 3 s would be a deceleration of −10 m/s², just over 1 g — firmly into "hold on" territory.
Frequently Asked Questions
a = (v − u)/t — change in velocity over time. 0→30 m/s in 10 s = 3 m/s². Negative means slowing.
m/s² — velocity changes that many m/s each second. Also g (÷9.81) for big accelerations.
Speed = how fast; velocity = speed + direction; acceleration = rate velocity changes. Turning is acceleration too.
s = ut + ½at², or s = (u+v)/2 × t. 0→30 m/s in 10 s at 3 m/s² → 150 m.
Acceleration as multiples of 9.81 m/s². 3 m/s² ≈ 0.31 g. Pilots pull up to ~9 g.