Kinematics
9th Grade Science · 12 lessons
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Lessons in this unit
- 1Distance, Displacement, and Why They DifferDistance is the total path length travelled; displacement is the straight-line vector from start to finish. Run one lap of a 400 m track and your distance is 400 m but your displacement is zero, because you ended where you began.Experiment
- 2Speed Is a Ratio, Velocity Is a VectorAverage speed is distance divided by time. Velocity is displacement divided by time, so it carries a direction. A car going round a roundabout at a steady 30 km/h has constant speed but changing velocity, because its direction keeps changing.Experiment
- 3Acceleration: the Rate Velocity ChangesAcceleration is change in velocity divided by the time taken, measured in metres per second squared. It is negative when an object slows, and it is non-zero even at constant speed if the direction is changing.Experiment
- 4Reading a Distance-Time GraphOn a distance-time graph the gradient is the speed. A straight sloping line means constant speed, a horizontal line means the object is stationary, and a curve that gets steeper means the object is speeding up.Experiment
- 5Velocity-Time Graphs and the Area UnderneathOn a velocity-time graph the gradient gives acceleration and the area under the line gives displacement. A trapezium under the line is often the quickest way to find how far something travelled while speeding up.Lesson
- 6The Equations of MotionFor constant acceleration, four equations link displacement, initial and final velocity, acceleration and time. The most used are v = u + at and s = ut + ½at². Pick the equation that contains the three quantities you know and the one you want.Experiment
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