In physics, acceleration is a vector derived quantity that indicates the change in velocity per unit time. According to Newtonian mechanics, a particle cannot follow a curved path unless certain acceleration acts on it as a consequence of the action of a force, since if it did not exist, its motion would be rectilinear. Likewise, a particle in rectilinear motion can only change its speed under the action of acceleration in the same direction as its velocity.
For each instant or point of the trajectory, a velocity vector is defined that, in general, changes both in module and in direction when passing from one point to another on the trajectory. The direction of the velocity will change because the velocity is tangent to the path and the path is generally not straight. The figure represents the velocity vectors corresponding to the instants t and t+Δt, when the particle passes through the points P and Q, respectively. The vector change in the velocity of the particle during that time interval is indicated by Δv, in the vector triangle at the bottom of the figure. The mean acceleration is defined of the particle, in the time interval Δt.
Acceleration measurement can be done with a data acquisition system and a simple accelerometer. Electronic accelerometers are made to measure acceleration in one, two, or three directions. It have two conductive elements, separated by a material that varies its conductivity depending on the measurements, which in turn will be relative to the acceleration of the whole.
An object can only gain acceleration when a resulting force acts on the object. With constant force, the acceleration of an object is inversely proportional to its mass. For example, a light car can be pushed more easily than a heavy truck. When the resulting force is 0, the object will not accelerate either. No resulting force will work on a car running at a constant speed. The force that drives the car is equal to the frictional force of wind and road surface that brakes the car, so that the car does not experience acceleration. Also, a car will not sink through the asphalt (acceleration down), because the gravity that pushes the car down is equal to the normal force that pushes the car up.
The usual unit to indicate acceleration is m/s2. For vehicles such as cars and speed boats, the acceleration time from 0 to 100 km/h is often specified.
| Base value | (Gal, or cm/s2) | (ft/s2) | (m/s2) | (Standard gravity, g0) |
|---|---|---|---|---|
| 1 Gal, or cm/s2 | 1 | 0.0328084 | 0.01 | 0.00101972 |
| 1 ft/s2 | 30.4800 | 1 | 0.304800 | 0.0310810 |
| 1 m/s2 | 100 | 3.28084 | 1 | 0.101972 |
| 1 g0 | 980.665 | 32.1740 | 9.80665 | 1 |
