Table of Contents
What Is Acceleration?
Acceleration is the rate of change of velocity with respect to time. It is a vector quantity with both magnitude and direction. When an object speeds up, slows down, or changes direction, it is accelerating. In SI units, acceleration is measured in meters per second squared (m/s²).
Acceleration is one of the fundamental concepts in Newtonian mechanics. Newton's second law states that the net force on an object equals its mass times its acceleration (F = ma). This connects kinematics with dynamics and forms the basis for analyzing everything from falling objects to rocket launches.
Kinematic Equations
Where a is acceleration, vf is final velocity, v0 is initial velocity, t is time, and d is distance. These assume constant acceleration throughout the time interval.
Common Acceleration Values
| Scenario | Acceleration | g-force |
|---|---|---|
| Free fall (Earth) | 9.81 m/s² | 1 g |
| Sports car 0-60 | ~6.3 m/s² | 0.64 g |
| Space Shuttle launch | ~29.4 m/s² | 3 g |
| Roller coaster peak | ~39 m/s² | 4 g |
| Fighter jet turn | ~88 m/s² | 9 g |
Frequently Asked Questions
Can acceleration be negative?
Yes, negative acceleration (deceleration) means the object is slowing down in the positive direction. A car braking from 30 m/s to 0 m/s has negative acceleration relative to its direction of travel. The sign depends on your chosen coordinate system.
What is the difference between acceleration and velocity?
Velocity describes how fast an object is moving and in what direction. Acceleration describes how quickly the velocity is changing. An object at constant velocity has zero acceleration. An object at rest that begins to move has non-zero acceleration even though its initial velocity is zero.
How many g-forces can a human survive?
Trained pilots in pressure suits can withstand up to about 9g for short periods. Untrained humans typically lose consciousness around 4-6g. The highest survived g-force was 214g in a 1954 rocket sled deceleration test by Col. John Stapp, lasting only a fraction of a second.