Beginner · 10 min
Changes in velocity
Calculate acceleration and predict velocity during a steady change.
Acceleration measures change
Velocity describes speed and direction. Acceleration is the change in velocity divided by the time taken. For motion along a straight line, choose a positive direction first. A positive acceleration changes velocity towards that direction; a negative acceleration changes it the other way. Acceleration is measured in metres per second squared (m/s²). An acceleration of 2 m/s² changes velocity by 2 m/s each second.
Worked example
A cart moving in the positive direction goes from 1 m/s to 7 m/s in 3 s. Acceleration = (7 − 1) ÷ 3 = 2 m/s²
Find the final velocity
When acceleration stays constant, multiply acceleration by time to find the change in velocity. Add this change to the initial velocity. Keep the signs: an object moving in the positive direction slows down while its acceleration is negative, until it stops. Zero acceleration means constant velocity, which can be zero or nonzero.
Worked example
Initial velocity = 10 m/s; acceleration = −2 m/s²; time = 3 s. Final velocity = 10 + (−2 × 3) = 4 m/s
Track a changing velocity
- Make a table for an object starting at 0 m/s with a constant acceleration of 2 m/s². List its velocity after 1, 2, 3, and 4 seconds.
- Explain the difference between moving at 2 m/s and accelerating at 2 m/s².