Physics (9-1) - 0972 CIE

Motion

Overview

Everything around you is either moving or could be set moving, and physics begins by describing that motion precisely. How fast is a sprinter going? Is a car speeding up or slowing down? How far does a dropped stone fall in two seconds? Every one of these questions is answered with a handful of equations and two simple graphs.

In this lesson you will define speed, velocity and acceleration, then read and draw distance-time and speed-time graphs with confidence. You will calculate speed from a gradient, distance from an area, and handle free fall and terminal velocity. By the end you should be able to look at a graph and tell its whole story.

Objectives

Define speed as distance travelled per unit time; recall and use the equation s v = t
Define velocity as speed in a given direction
Recall and use the equation total distance travelled average speed = total time taken
Sketch, plot and interpret distance-time and speed-time graphs
Determine, qualitatively, from given data or the shape of a distance-time graph or speed-time graph when an object is: (a) at rest (b) moving with constant speed (c) accelerating (d) decelerating
Calculate speed from the gradient of a straight- line section of a distance-time graph
Calculate the area under a speed-time graph to determine the distance travelled for motion with constant speed or constant acceleration
State that the acceleration of free fall g for an object near to the surface of the Earth is approximately constant and is approximately
[Supplement] Define acceleration as change in velocity per unit time; recall and use the equation ∆v a = ∆t
[Supplement] Determine from given data or the shape of a speed-time graph when an object is moving with: (a) constant acceleration (b) changing acceleration
[Supplement] Calculate acceleration from the gradient of a speed-time graph
[Supplement] Know that a deceleration is a negative acceleration and use this in calculations
[Supplement] Describe the motion of objects falling in a uniform gravitational field with and without air/ liquid resistance, including reference to terminal

Lesson Note

Motion is the foundation of mechanics: forces, momentum and energy all build on it. Examiners love motion because it links words, equations and graphs at once. Read a speed-time graph correctly and you can pull out speed, acceleration and distance from a single picture, which is why this topic appears in almost every paper.

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Lesson Evaluation

Congratulations on completing the lesson on Motion. Now that youve explored the key concepts and ideas, its time to put your knowledge to the test. This section offers a variety of practice questions designed to reinforce your understanding and help you gauge your grasp of the material.

You will encounter a mix of question types, including multiple-choice questions, short answer questions, and essay questions. Each question is thoughtfully crafted to assess different aspects of your knowledge and critical thinking skills.

Use this evaluation section as an opportunity to reinforce your understanding of the topic and to identify any areas where you may need additional study. Don't be discouraged by any challenges you encounter; instead, view them as opportunities for growth and improvement.

A car travels 150 m in 10 s. Its average speed is: A. 1.5 m/s B. 15 m/s C. 150 m/s D. 1500 m/s Answer: B
On a distance-time graph, a horizontal line means the object is: A. accelerating B. moving at constant speed C. at rest D. decelerating Answer: C
On a speed-time graph, the distance travelled is given by: A. the gradient of the line B. the area under the line C. the highest point D. the time axis intercept Answer: B
A car speeds up from 10 m/s to 30 m/s in 5 s. Its acceleration is: A. 2 m/s2 B. 4 m/s2 C. 6 m/s2 D. 100 m/s2 Answer: B
A skydiver reaches terminal velocity when: A. weight is zero B. drag is zero C. drag equals weight D. the parachute opens Answer: C