National 5PhysicsSQARevision NotesDynamicsAccelerationMeasuring Acceleration

Measuring Acceleration (SQA National 5 Physics): Revision Note

Exam code: X857 75

Katie M

Written by: Katie M

Reviewed by: Leander Oates

Updated on

Measuring acceleration

  • Acceleration is the rate of change of velocity, or the change in velocity per unit time

  • The quantities required to determine the acceleration of a moving object are

    • the initial velocity u of the object

    • the final velocity v of the object

    • the time interval t between these velocities

  • The experimental methods for measuring acceleration are similar to those used for measuring speed

  • Apparatus for measuring acceleration:

    • Trolley

    • Ramp

    • Card with one or two sections attached to the trolley

    • Ruler

    • Stop clock

    • One or two light gates connected to a computer or electronic timers

Measuring acceleration with one light gate

Acceleration from rest

  • This method uses one light gate and a single card to measure acceleration

Trolley rolls down ramp; light gate measures card passing time using electronic timer, and stop-clock tracks time to reach gate. Initial velocity is zero.
In this method, acceleration is determined from time interval between the beginning of the motion, where initial velocity is zero, to the final velocity at the bottom of the ramp

  • Method:

    • Set up the ramp with one light gate (attached to a computer or timer) at the bottom of the ramp

    • Measure the length of the card d using a ruler

    • Release the trolley from rest (initial velocity u space equals space 0) at the top of the ramp and start the stop clock

    • As the trolley passes the light gate, the timer records the time t subscript 1 the card blocks the light beam

    • Use the stop clock to measure the time t subscript 2 for the trolley to reach the light gate

    • Calculate the final velocity v using the equation:

    v space equals space d over t subscript 1

    • Calculate the acceleration a of the trolley using the equation:

    a space equals space v over t subscript 2

Acceleration at a point

  • This method uses one light gate and a double card (two sections separated by a gap) to measure acceleration at a single point

Diagram of a ramp setup with a trolley, light gate, and computer. Cards measure velocity via interrupting a beam; a ruler measures card length.
In this method, acceleration is determined at the point where the light gate is positioned using the change in velocity of the two sections of card and the time interval between the cards

  • Method:

    • Set up the ramp with one light gate (attached to a computer) at any point

    • Measure the length d of each mask using a ruler (ideally, these should be the same length)

    • Release the trolley from rest at the top of the ramp

    • As the trolley passes the light gate, the computer records the time t subscript 1 that the first card blocks the light beam and the time t subscript 2 that the second card blocks the light beam

    • The computer also records the time t between each card passing through the light beam

    • Calculate the initial velocity u using the equation:

    u space equals space d over t subscript 1

    • Calculate the final velocity v using the equation:

    v space equals space d over t subscript 2

    • Calculate the acceleration a of the trolley at a point using the equation:

    a space equals space fraction numerator v space minus space u over denominator t end fraction

Measuring acceleration with two light gates

  • This method uses two light gates and a single card to measure the average acceleration between two points

Diagram of a trolley with a card moving down a ramp through two light gates measuring initial and final velocity using electronic timers and a ruler.
In this method, acceleration is determined from the instantaneous speed of the trolley at each light gate and the time interval between the light gates

  • Method:

    • Set up the ramp with two light gates (attached to a computer or timers) at the bottom of the ramp

    • Measure the length of the card d using a ruler

    • Release the trolley from rest at the top of the ramp

    • As the trolley passes through light gate 1 and light gate 2, times t subscript 1 and t subscript 2 are recorded, respectively, as the card blocks the light beam

    • Use the stop clock to measure the time t for the trolley to pass between the light gates

    • Calculate the initial velocity u using the equation:

    u space equals space d over t subscript 1

    • Calculate the final velocity v using the equation:

    v space equals space d over t subscript 2

    • Calculate the average acceleration a with bar on top of the trolley using the equation:

    a with bar on top space equals space fraction numerator v space minus space u over denominator t end fraction

Evaluating the experiment

  • The main source of error in these experiments arises from human error in the measurements of

    • distance, when using a ruler

    • time, when using a stop clock

  • The experiments could be improved by

    • using an electronic timer instead of a stop clock to record the time t between the gates

    • releasing the trolley from the same point each time

    • taking repeat readings and averaging the results

Examiner Tips and Tricks

Exam questions about experimental procedures tend to focus on identifying required measurements for an investigation. For the measurement of acceleration, these are

  • the length of the card attached to the trolley

  • the time for the card to pass through the light gates (to calculate instantaneous speed)

  • the time between positions of initial and final velocities (this depends on the method used)

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    Author
    Reviewer
    Katie M

    Author: Katie M

    Expertise: Physics Content Creator

    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.

    Leander Oates

    Reviewer: Leander Oates

    Expertise: Physics Content Creator

    Leander graduated with First-class honours in Science and Education from Sheffield Hallam University. She won the prestigious Lord Robert Winston Solomon Lipson Prize in recognition of her dedication to science and teaching excellence. After teaching and tutoring both science and maths students, Leander now brings this passion for helping young people reach their potential to her work at SME.