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Uniform rectilinear motion

Lessons 5 · 1 lessons · P.Q. Habibullayev, A. Boydedayev, A.D. Bahromov, S.O. Burxonov. Physics Grade 7, revised and enlarged 4th edition. “O‘zbekiston milliy ensiklopediyasi” State Scientific Publishing House, Tashkent, 2017
5

The idea of uniform rectilinear motion

Textbook: pp. 26–27
GoalKnow what uniform rectilinear motion is and recognise it.
New words
rectilinear motion · to‘g‘ri chiziqli harakatuniform motion · tekis harakatequal time intervals · teng vaqt oralig‘ivelocity · tezlik
Explanation

Motion with a straight-line trajectory is called rectilinear motion. If a body makes equal displacements in any equal time intervals, its motion is uniform. So in uniform rectilinear motion the body covers the same distance every second and every minute and does not change direction. Such motion is steady and one-way. Perfectly uniform motion is rare in practice: a car travelling on a straight road at constant speed or the steps of an escalator move approximately in this way. To check whether motion is uniform we measure the path in equal time intervals and compare the values.

Worked examples
An escalator step moves 1 m every 2 s, 2 m in 4 s, 3 m in 6 s: equal intervals give equal paths, so the motion is uniform.
A cyclist travelled 20 m in 10 s and 35 m in the next 10 s. Equal times give different paths, so the motion is not uniform.
Class activity

“Uniform or not?”: with a stopwatch and tape measure the teacher measures every 2 s the path of a slowly rolling toy car; the class decides if the motion is uniform. Safety: do not run along the track.

Practice
1
What motion is called uniform rectilinear motion?
2
A body travels 12 m in 3 s and another 12 m in the next 3 s. Could this be uniform motion?
3
A body goes 10 m in 5 s and 20 m in the next 5 s. Is the motion uniform?
4
Why is perfectly uniform motion rare in practice?