What acceleration measures
Acceleration is the rate at which speed changes. A car that gains 10 mph every second accelerates faster than one that gains 5 mph per second. In physics it is measured in meters per second squared (m/s²): the change in speed, in m/s, during each second. In the US you will also see feet per second squared, and for vehicles and aircraft it is often expressed in g, multiples of Earth’s gravity.
The formulas
- Acceleration = (final speed − initial speed) ÷ time
- Acceleration in g = acceleration ÷ 9.80665 m/s²
- Distance covered = (initial speed + final speed) ÷ 2 × time
The distance formula assumes a constant acceleration, which is a good approximation for most everyday cases.
Worked example
A car goes from 0 to 60 mph in 8 seconds.
- 60 mph is 26.82 m/s.
- Acceleration = 26.82 ÷ 8 = 3.35 m/s², or 11.0 ft/s².
- In g: 3.35 ÷ 9.81 = 0.34 g.
- Distance covered: 13.41 m/s average × 8 s = 107 m, about 352 ft.
Reaching 60 mph in 3 seconds would take 0.91 g, which is supercar territory.
Typical accelerations
| Situation | Acceleration |
|---|---|
| Family car, 0–60 mph in 9 s | about 0.3 g |
| Sports car, 0–60 mph in 4.5 s | about 0.6 g |
| Supercar, 0–60 mph in 2.7 s | about 1 g |
| Hard braking on dry pavement | 0.8 to 1 g |
| Airliner takeoff roll | about 0.25 g |
| Roller coaster launch | 1 to 2 g |
Negative acceleration
If the final speed is lower than the initial speed, the acceleration is negative: the object is slowing down. Physicists still call this acceleration; in everyday language it is deceleration or braking. Enter 60 mph as the initial speed and 0 as the final speed to see the braking rate of a car that stops in a given time.
Acceleration and force
Acceleration is what a net force produces: by Newton’s second law, a = F ÷ m. Doubling the engine force on the same car doubles the acceleration, while doubling the mass halves it. Use the force calculator to go from acceleration to the force required.
Limits of the model
Real cars do not accelerate evenly: they pull hardest at low speed and in lower gears, then less as air drag grows. The calculator gives the average acceleration over the interval, which is what a 0–60 time actually measures.