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First teaching 2014

Last exams 2024

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Acceleration (DP IB Physics: SL)

Revision Note

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Acceleration

  • Acceleration is defined as the rate of change in velocity
    • In other words, it describes how much an object's velocity changes every second

  • The equation below is used to calculate the average acceleration of an object:

 

acceleration space equals fraction numerator space change space in space velocity over denominator time space taken end fraction

 

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

  • Where:
    • a = acceleration in metres per second squared (m s–2)
    • Δv = change in velocity in metres per second (m s–1)
    • t = time taken in seconds (s)

  • The change in velocity is the difference between the initial and final velocity, as written below:

change in velocity = final velocity − initial velocity

Equations linking displacement, velocity, and accelerationEquation Definitions, downloadable AS & A Level Physics revision notes

Speeding Up and Slowing Down

  • An object that speeds up is accelerating
  • An object that slows down is decelerating
  • 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)

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 50 m s–1 to 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.

Part (a)

Step 1: List the known quantities

    • Initial velocity = 50 m s–1
    • Final velocity = 42 m s–1

Step 2: Write the relevant equation

change in velocity = final velocity − initial velocity

Step 3: Substitute values for final and initial velocity

change in velocity = 42 − 50 = −8 m s–1

Part (b)

Step 1: List the known quantities

    • Change in velocity, Δv = −8 m s–1
    • Time taken, t = 30 s

Step 2: Write the relevant equation

 

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

Step 3: Substitute the values for change in velocity and time

 

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

Step 4: Interpret the value for deceleration

    • 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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Katie M

Author: Katie M

Expertise: Physics

Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.