Topic 8.3
Motion along a straight line
at constant acceleration
Acceleration
Aims
In this experiment you will be measuring the acceleration of a trolley as it accelerates down
an inclined plane. You will also consider how to minimise errors when timing the trolley.
You will then plan a suitable method to investigate the relationship between the acceleration
and the inclination of the slope.
Safety
 Care should be taken when lifting or moving the ramps.
 Beware of falling trolleys. Suggest a safe method to use to stop the trolley when it reaches
the end of the slope.
Equipment, materials and method
1 For this experiment you will need a ramp resting on a wooden block (or similar), a trolley,
a metre ruler, a set square, a second wooden block (to stop the trolley), a G-clamp,
2 stands, bosses and clamps and a stopwatch to time the trolley.
2 Set up the apparatus as shown below. On the diagram, draw the timing equipment used to
determine the mean time t for the trolley to travel 1.00 m from rest.
3 Calculate the acceleration of the trolley given that a =
2d
, where d = 1.00 m.
t2
4 Measure the angle θ using a trigonometric method.
5 You can assume that there is a linear relationship between the acceleration of the trolley
down the inclined plane and sin θ. Plan an extension to your experiment to investigate the
relationship between the acceleration a and sin θ. Consider how you will display your
results graphically.
6 Carry out your investigation.
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Topic 8.3
Motion along a straight line
at constant acceleration
Questions
1 Explain why using a trigonometric method is better than using a protractor to determine θ.
1
2s
is a rearrangement of s = ut + at2.
2
2
t
3 (a) Estimate the error in each timing.
2 Explain how the equation a =
(b) Explain why repeating measurements is particularly important in this experiment.
Results
Present your findings on a graph.
Discussion
Discuss whether your results show any evidence for a linear relationship between the
acceleration a and sin θ.
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Topic 8.3
Motion along a straight line
at constant acceleration
Technicians Notes
Equipment and materials required
Each student or pair of students will require the following equipment:
 a ramp, approx 1.5 m long
 a wooden block to support ramp
 a trolley
 a metre ruler
 a set square
 second wooden block to place at the end of the ramp to stop the trolley
 sticky-tac to secure the second wooden block (or use a G-clamp)
 two retort stands, bosses and clamps (to support ramp or light sensors)
 a stopwatch or data logger with light gates (It may be necessary to fix an interrupter card
to the trolley to intercept the light gates.)
 graph paper
Safety
 Care should be taken when lifting or moving the ramps.
 A wooden block should be placed at the end of the ramp to stop the trolley. It may need
fixing with a small amount of sticky-tac. Alternatively a student’s bag might be an
appropriate stopping device!
 Ensure that ramps are not in a position where they or the trolleys are likely to fall off
benches.
 If there is room, the experiment might be safest done on the floor. If not, protect the
benches and feet from heavy trolleys.
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Topic 8.3
Motion along a straight line
at constant acceleration
Teachers Notes
Aims
 To measure the time it takes for a trolley to move down an inclined plane and hence
calculate the acceleration.
 To understand and minimise the uncertainties involved when timing an event.
 To plan a suitable method to investigate the relationship between the acceleration of the
trolley down an inclined plane and sin θ, where θ is the angle of inclination.
Safety
 A wooden block should be placed at the end of the ramp to stop the trolley. It may need
fixing with a small amount of sticky-tac.
 Ensure that ramps are not in a position where they or the trolleys are likely to fall off
benches.
 Protect benches and feet from heavy trolleys.
Teaching notes
4 A data logger with light gates is preferable to a stopwatch. However, this is not always
practical. You could consider having some groups use a data logger while others use a
stopwatch. The groups could compare results or, time permitting, repeat the experiment
with an alternative timing method. A third method might be to use ticker tape to measure
time.
5 If using a stopwatch, ensure that students observe the trolley at eye level when measuring
the distance travelled. This may mean that they have to move along the ramp with the
trolley. Alternatively, one person counts down (3, 2, 1, go) and releases the trolley,
another starts the stopwatch on ‘go’ and, watching the 1 m line all the time, stops the clock
as the trolley passes. They need to be clear which end of the trolley is being measured
(that is, the front or the back).
6 Alter the angle of inclination by moving the wooden block supporting the ramp.
7 The practical part of this experiment may take in excess of 20 minutes.
8 Note that in order to plot a graph of acceleration a against sin θ, the actual angle does not
need to be calculated.
Answers to questions
1 The trigonometric method is preferable because the percentage uncertainty of measuring a
small angle with a protractor is very large.
1 2
at the value of u (the initial velocity) is zero, the
2
2s
equation can be simply rearranged to make a the subject, giving a = 2 .
t
3 (a) The range of values can be used to make an estimate of the uncertainty, where the
uncertainty is equal to half the range.
2 Since in the equation s = ut +
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Topic 8.3
Motion along a straight line
at constant acceleration
(c) Repeat measurements are important due to uncertainties in the measurements. For
example, these could be due to variations in friction, human reaction time, or whether
the trolley runs straight.
Discussion
The results of this experiment are dependent on the equipment used (precision, friction of
trolley, etc.). A straight line graph supports the theory of linearity. The discussion may
present opportunity to discuss the benefits of taking extra measurements around a particular
area of the graph, for example near the origin, to investigate whether the graph is linear.
Practical assessment opportunities
4 PSA – Selecting and using equipment: 0–3 marks
(Following instructions and group work; organisation and safety assessed at end of
course.)
5 ISA preparation:
practical task – practice in recording measurements, accurate measurement of an angle,
estimating errors and plotting a graph
written task Section A and B – opportunities to analyse data and errors, draw conclusions
and to evaluate the strength of the conclusion
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