<img src="https://d5nxst8fruw4z.cloudfront.net/atrk.gif?account=iA1Pi1a8Dy00ym" style="display:none" height="1" width="1" alt="" />
Skip Navigation
Due to system maintenance, CK-12 will be unavailable on 8/19/2016 from 6:00p.m to 10:00p.m. PT.

Average Acceleration

Define and calculate average acceleration using formulas

Atoms Practice
Estimated1 minsto complete
Practice Average Acceleration
Estimated1 minsto complete
Practice Now
Turn In
Average Acceleration

A space shuttle, such as the Atlantis, must accelerate to 28,968 km/h to escape from Earth's orbit

Credit: Courtesy of NASA
Source: http://spaceflight.nasa.gov/gallery/images/shuttle/sts-125/html/sts125-s-025.html
License: CC BY-NC 3.0

To escape from Earth's orbit, space shuttles such as the Atlantis shown here must accelerate to 28,968 kilometers per hour, called the shuttle's escape velocity.

Average Acceleration

An object whose velocity is changing is said to be accelerating. Average acceleration, \begin{align*}\overline{a}\end{align*} is defined as the rate of change of velocity, or the change in velocity per unit time. The units of acceleration are distance over time squared. A symbol with a bar over it is read as average – so a-bar is average acceleration.


Example 1

A car accelerates along a straight road from rest to +60.0 km/h in 5.00 s. What is the magnitude of its average acceleration?

The acceleration in this problem is read as kilometers per hour per second. In general, it is undesirable to have two different units for the same quantity in a unit expression. In this case, it is undesirable to have both hours and seconds. To eliminate this problem, we convert the hour units to seconds. Converting the original 60.0 km/h to m/s, gives 17.0 m/s.

\begin{align*}\frac{17.0\ m/s}{5.00\ s}=3.40 \ m/s^2 \end{align*}

The acceleration is 3.40 m/s2.

Example 2 

An automobile is moving along a straight highway in the positive direction and the driver steps on the brakes. If the initial velocity is +15.0 m/s and 5.0 s is required to slow down to +5.0 m/s, what was the car’s acceleration?

\begin{align*}\overline{a} = \frac{\Delta v}{\Delta t} = \frac{-10.0 \ m/s}{5.0 \ s} = -2.0 \ m/s^2\end{align*}

Note that an acceleration is merely a change in velocity. This change can be either positive or negative. A negative change, such as that in the example problem above, is sometimes called negative acceleration or deceleration.


  • Average acceleration is the rate of change of velocity, or the change in velocity per unit time.


  1. The velocity of a car increases from +2.0 m/s to +16.0 m/s in a time period of 3.5 s. What was the average acceleration?
  2. If an automobile slows from +26 m/s to +18 m/s in a period of 4.0 s, what was the average acceleration?
  3. If a runner increases his velocity from 0 m/s to +20 m/s in 2.0 s, what was his average acceleration?
  4. If a runner decreases his velocity from +20 m/s to +10 m/s in 2.0 s, what was his average acceleration?

Notes/Highlights Having trouble? Report an issue.

Color Highlighted Text Notes
Please to create your own Highlights / Notes
Show More

Image Attributions

  1. [1]^ Credit: Courtesy of NASA; Source: http://spaceflight.nasa.gov/gallery/images/shuttle/sts-125/html/sts125-s-025.html; License: CC BY-NC 3.0

Explore More

Sign in to explore more, including practice questions and solutions for Average Acceleration.
Please wait...
Please wait...