Let's suppose that there is a body which is moving with non-uniform velocity in the straight line. In the first hour it travels with a velocity of 50 km per hour and in the second hour it stops for 30 minutes and then in next 30 minutes it travels with a speed of 100 km per hour.

So can we call the motion of the body as uniform motion becuase in the first hour it covers 50 km and in the second hour also it covers 50 km and by the definition of uniform motion we know that a body is said to be in uniform motion if it covers equal distances in equal intervals of time and here the body is covering equal distances in the equal intervals of one hour. Or in simple words, "Is uniform motion possible for a body having non-uniform velocity ?"

I am totally confused here any help would be highly appreciated.


2 Answers 2


No, uniform velocity means that the instantaneous velocity is constant, i.e., the acceleration during some finite time interval is zero.

In the example you invented we could say there are three different time intervals of uniform motion. During the first hour the velocity is 50 km/hr in a fixed direction and is uniform. During the next half hour the velocity is 0 km/hr and therefore a different uniform velocity. And the third uniform velocity is 50 km/hr in a fixed direction.

Note that the instantaneous velocity was not constant for the entire 2 hours, therefore the velocity was not uniform for 2 hours. The fact that the first and third intervals had the same velocity has nothing to do with uniform velocity.

Edit addition: Another use of the word uniform is in the phrase uniform circular motion. Here, uniform refers to the speed of the object because the velocity is not constant and there is an acceleration. Circular implies that the radius of curvature of the path is constant. So uniform circular motion means the instantaneous speed is constant, the acceleration is always perpendicular to the velocity, and the path is a circle.

Context is important when interpreting the meaning of the word uniform.


In physics, you give something a name because the name represents something to you.

To me, "uniform motion" implies "no acceleration or deceleration". In that case, the motion you describe is not uniform.

You were using a definition "constant displacement in one hour". That is true if you pick your hours "just right". But if you picked a different starting point for your hour (say from 0:30 to 1:30) you would see that the definition no longer holds.

If your definition of "uniform" requires very specific sampling, then the thing you are sampling is not as uniform as you think.

This is (somewhat) related to the Nyqvist criterion: if you sample a periodically varying phenomenon with insufficient frequency, you will not be able to determine the nature of that phenomenon. Example: if you only look at the sun at noon every day, you would think the sun barely moves (it goes up and down in the sky a bit with a period of one year). Someone who looks at the sun multiple times a day can tell you it's rising, setting, ...


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