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Acceleration (HL IB Physics)

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Acceleration

  • Acceleration is defined as:

The rate of change of velocity

  • Acceleration is a vector quantity and is measured in metres per second squared (m s–2)
    • It describes how much an object's velocity changes every second
  • The average acceleration of an object can be calculated using:

a v e r a g e space a c c e l e r a t i o n space equals space fraction numerator c h a n g e space i n space v e l o c i t y space over denominator t i m e space t a k e n end fraction

a space equals space fraction numerator increment v over denominator increment t end fraction

  • Where:
    • a = average acceleration (m s–2)
    • increment v = change in velocity (m s–1)
    • increment t = total time taken (s)
  • The change in velocity is the difference between the initial and final velocity, as written below:

change in velocity = final velocity − initial velocity

increment v space equals space open parentheses v space minus space u close parentheses

Equations linking displacement, velocity, and acceleration

Equation Definitions, downloadable AS & A Level Physics revision notes

Instantaneous Acceleration

  • The instantaneous acceleration is the acceleration of an object at any given point in time
  • This could be for an object with a constantly changing acceleration
    • An object accelerating is shown by a curved line on a velocity-time graph

What is a negative acceleration called?

  • The acceleration of an object can be positive or negative, depending on whether the object is speeding up or slowing down
    • If an object is speeding up, its acceleration is positive
    • If an object is slowing down, its acceleration is negative (deceleration)
  • However, acceleration can also be negative if it is accelerating in the negative direction

Acceleration Examples, downloadable IGCSE & GCSE Physics revision notes

A rocket speeding up (accelerating) and a car slowing down (decelerating)

Worked example

A Japanese bullet train decelerates at a constant rate in a straight line.

The velocity of the train decreases from an initial velocity of 50 m s–1 to a final velocity of 42 m s–1 in 30 seconds.

(a)
Calculate the change in velocity of the train.
(b)
Calculate the deceleration of the train, and explain how your answer shows the train is slowing down.
 

Answer:

(a)

  • The change in velocity is equal to

increment v space equals space v space minus space u

  • Where:
    • Initial velocity, u = 50 m s–1
    • Final velocity, v = 42 m s–1

increment v = 42 − 50 = −8 m s–1

(b)

  • Acceleration is equal to

a space equals space fraction numerator increment v over denominator increment t end fraction

  • Where the time taken is Δt = 30 s

a space equals space fraction numerator negative 8 over denominator 30 end fraction space equals space minus 0.27 space straight m space straight s to the power of negative 1 end exponent

  • The answer is negative, which indicates the train is slowing down

Examiner Tip

Remember the units for acceleration are metres per second squared, m s–2. In other words, acceleration measures how much the velocity (in m s–1) changes every second, (m s–1) s–1

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    Ashika

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    Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.