The acceleration formula
Acceleration is the rate of change of velocity: a = (vf - vi) / t, where vf is the final velocity, vi the initial velocity, and t the time. Speeding up from 0 to 27 m/s in 9 s gives 3 m/s². A negative result means deceleration. You can find the velocities themselves with the velocity calculator.
How to use this calculator
Enter the final velocity, the initial velocity (use 0 for a standing start), and the time in seconds. The result is in meters per second squared (m/s²), the SI unit of acceleration. For comparison, gravity near Earth's surface is about 9.8 m/s². Acceleration changes speed, and changing speed changes the kinetic energy an object carries.
- Signs matter. Pick one direction as positive and keep both velocities in that frame. A car going from 27 m/s to 0 m/s in 9 s gives −3 m/s², i.e. braking.
- Time cannot be zero. A zero interval would mean an instant velocity change, which the formula cannot express.
- Constant acceleration is assumed. If the rate varies wildly, treat the answer as an average over the whole interval.
Acceleration and force
Acceleration links directly to force through Newton's second law, F = m·a. Once you know acceleration, multiply by mass to find the force involved with the force calculator. A larger acceleration over the same time means a bigger velocity change.
Frequently asked questions
- How do I calculate acceleration?
- Subtract initial velocity from final velocity, then divide by time: a = (vf - vi) / t.
- What does a negative acceleration mean?
- It means the object is slowing down (decelerating) in the chosen direction.
- What are the units of acceleration?
- Meters per second squared (m/s²) in SI units.
- What is the acceleration due to gravity?
- About 9.8 m/s² near Earth's surface, often rounded to 9.81 m/s².
- Do my velocity and time units have to match?
- Yes — mixing units is the most common mistake here. Velocities in m/s with time in seconds give m/s²; if your speeds are in km/h, divide by 3.6 to convert to m/s before entering them.