K326 / K327 / 2027
Kinematics overview

Chapter revision

Revision summary

Key ideas, equations and common mistakes. Open any topic below for the full explanation.

Average speed
Total distance / total elapsed time. Include stops. Unit: m/s.
Acceleration
(v - u) / t. Constant throughout a uniform interval; otherwise an average. Unit: m/s2.
Free fall near Earth
g is approximately 10 m/s2 downwards. Air resistance is neglected.
What height, gradient and area tell you
FeatureDistance-timeSpeed-time
HeightDistance in mSpeed in m/s
GradientSpeedAcceleration
Horizontal lineAt restConstant speed; rest only at zero
AreaDoes not give distance or displacementDistance travelled

Measure free-fall acceleration

Two light gates time the passage of the same short flag. Speed = flag length / blocked duration. For approximately uniform acceleration, assign each speed to the midpoint of its blocked interval, then use the time between those midpoints in a = (v - u) / t. The supplied speeds 1.00 and 2.00 m/s at 0.0100 and 0.1120 s give about 9.8 m/s2 downwards. This is a free-fall determination only if other forces are negligible. Align the flag and gates, use a suitable timer and keep the attached body out of the beam; repeats do not fix a wrong flag length or time interval.

Check your answer

  • Identify the axes and the time interval.
  • Use changes on both axes for a gradient.
  • Split graph areas into rectangles and triangles; triangle area = (1/2) x base x height.
  • Give units, and direction when the quantity needs it.
  • State assumptions such as uniform acceleration or negligible air resistance.
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Practise exam questions

Write your answer first, then tick the mark points it makes.

Exam-style question

A cyclist starts from rest and accelerates uniformly to 6.0 m/s in 4.0 s. She then rides at a constant 6.0 m/s for a further 10 s. Calculate the total distance she travels in the 14 s. [2]

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Exam-style question

Define acceleration. A car speeds up uniformly from 12 m/s to 30 m/s in 6.0 s. Calculate its acceleration. [3]

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Exam-style question

A girl walks in a straight line away from her home. A graph of her distance from home against time has three straight parts: from (0 s, 0 m) to (40 s, 60 m), then flat from 40 s to 70 s, then from (70 s, 60 m) to (100 s, 150 m). Describe her motion in each part and calculate her speed in the last part. [3]

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Exam-style question

A stone is dropped from rest from a bridge and hits the water 1.5 s later. Air resistance is negligible and the acceleration of free fall is 10 m/s2. Calculate the speed of the stone as it hits the water and the height of the bridge above the water. [3]

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Quick recall

Card 1 of 5. Answer in your head, then check.

A cyclist travels 90 m in 15 s, waits for 5 s, then travels 30 m in 10 s. What is the average speed for the whole journey?

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