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  1. Glossary
  2. /Physics
  3. /Acceleration

What is Acceleration?

In short

Acceleration is the rate at which velocity changes with time, a=ΔvΔta = \dfrac{\Delta v}{\Delta t}a=ΔtΔv​. Its unit is the metre per second squared (m/s2\text{m/s}^2m/s2).

In simple words

An object accelerates when its speed rises, when it falls, or when its direction changes. A negative acceleration in the direction of motion means the object is slowing down, and it is often called deceleration. Constant acceleration gives a straight line on a velocity-time graph, and the slope of that line is the acceleration.

Example

A bus speeds up from 5 m/s5\ \text{m/s}5 m/s to 20 m/s20\ \text{m/s}20 m/s in 10 s10\ \text{s}10 s. Its acceleration is 20 m/s−5 m/s10 s=1.5 m/s2\dfrac{20\ \text{m/s} - 5\ \text{m/s}}{10\ \text{s}} = 1.5\ \text{m/s}^210 s20 m/s−5 m/s​=1.5 m/s2.

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  • Lessons on this topic
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Related terms

  • Speed and Velocity
  • Equations of Uniform Acceleration
  • Newton's Second Law (F = ma)

← All glossary terms

Learn it in

  1. Acceleration and Motion GraphsClass 9 to 10
  2. Describing MotionClass 9 to 10
  3. Equations of MotionClass 9 to 10
All lessons on this topic →

Practise

  1. A body on a spring moves along a line with the acceleration a = -9x (SI units), where x…Hard
  2. A body starts at x = 0 with a velocity of 3 m/s, and its acceleration is a = 8 - 2t (SI…
Medium
  • A particle moves along a line with x = t³ - 9t² + 24t (SI units)…Medium
  • A girl drops a stone into a dry well and hears it hit the bottom 2.4 s later…Hard
    • All problems on this topic →

    Quick questions

    1. A stone is dropped from rest. How far does it fall in 4.5 s? (g = 9.8 m/s²)Medium
    2. Ignoring air, a ball is thrown from the Earth's surface at the escape speed, but at 30°…Medium
    3. A lift rises from rest: it speeds up at 1 m/s² for 3 s, moves steadily for 5 s, then…Hard

    More Physics terms

    1. Position-Time Graph
    2. Acceleration Due to Gravity (g)
    3. Adiabatic Process
    4. Amplitude
    5. Angle of Incidence
    6. Angle of Reflection
    All Physics terms →

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