Every object or person moves and has a movement and a speed associated with a given time. The very word motion means an object or a person is moving at a particular pace or speed. Let us try to know whether the speed of the moving object has a uniform speed or non-uniform speed?
Uniform means constant, but what is non-uniform motion? Non-uniform means that which keeps varying or changing in speed.
Let us look at a scenario where Arun is training to run a marathon at a fundraiser event. His average speed has been 3 meters every second. Hence, throughout his usual route where he trains regularly, it is observed that for every second, he covers 3 meters. Arun maintains the same pace for a certain period of time.
This is described as uniform motion. As far as uniform motion is concerned, if we know the constant distance covered for each period of time along with the total time taken of the motion, we are able to calculate the total distance covered.
Constant distance covered (for each time period) X Total time duration = Total distance covered.
Suppose we assume that Arun ran at a uniform speed of 3 meters per second for a minute. How distance has he covered?
3 m/s x 1 min = ?
3 m/s x 60 sec = 180 meters
With the above calculation, keep in mind that units, the answer is 180 meters. In the same fashion, we can calculate the distance Arun would cover in 10 mins, 20 mins or even an hour. The calculation is as below, indicating how he maintains a constant speed.
3 m/s x (10 x 60) = 1800 meters
3 m/s x (20 x 60) = 3600 meters
3 m/s x (60 x 60) = 10800 meters
Uniform Motion
The distance travelled by an object in unit time is called speed. It is distance per unit time. The formula is as given below:
Distance/Unit time = Speed
The SI unit of speed is meters per second. In some instances, speed is also indicated as centimetres per second (cms/s), miles per hour (mi/hr) or kilometres per hour (km/h). However, the standard unit remains meters per second (m/s). Arun being a trained marathon runner, maintains a constant speed of 3 meters per second.
But in general, it is not easy to maintain a uniform speed no matter what activity we do, whether it is walking, running, riding a bicycle, riding in a car. In we take walking, for instance, we walk briskly for some time and as we get tired we tend to slow down our pace.
Most of the time, we are not even consciously in control of the speed. Most of the time, there are external factors that are beyond our control that affect our speed, like crowded streets, traffic jams or a procession on the road.
Non Uniform Motion
Here we discuss what is non uniform motion. You would have noticed that a man on a motorbike can go slower when in a traffic jam or go faster when on a highway. The same goes for any other vehicle too.
Such cases are called non-uniform motion were, as discussed, the speed of the object is not constant.
Is it possible to calculate the speed for non-uniform motion? Since motion is not uniform, the speed will vary at different points in time. Hence, while understanding non-uniform motion, we’ll pick the average speed in terms of the rate of motion.
Let us look at how to derive average speed:
A girl travels from point A to point B at 60 meters distance. She has been walking at varied rates of motion, which means non-uniform motion. She takes 60 seconds to reach point B, so she has covered 60 meters in 60 seconds. So what is her speed?
Rate of motion = covered 60 meters.
Average speed = In 60 seconds
Total distance covered/Elapsed time = Average speed
60 meters /60 seconds = 1 m/s
Hence the girl’s average speed is 1 m/s over 60 meters
The next day the girl travels 120 meters in 1 minute; the average speed would be as under
Rate of motion = covered 120 meters
Average speed = 1 minute = In 60 seconds
Total distance covered/Elapsed time = Average speed
120 meters /60 seconds = 2 m/s
Hence the girl’s average speed is 2 m/s over 120 meters
While calculating these sums, ensure we convert minutes to seconds and keep it to standard units, else students could commit silly mistakes.
The above example is applicable for any vehicle, too, where there are times when the vehicle travels, and other times it slows down or is even stuck in one place. In every instance, it is moving at varying speeds.
It could be zero meters per second or 3 meters per sec, or even 6 meters per second. The speed at each instance is called instantaneous speed.
Let look at another example to comparatively understand uniform motion and non-uniform motion:
Time |
Distance travelled by object A in meter |
Distance travelled by object B in meters |
---|---|---|
8:00 am |
10 |
12 |
8:15 am |
20 |
18 |
8:30 am |
30 |
24 |
8:45 am |
40 |
30 |
9:00 am |
50 |
35 |
By looking at the above table, object A has constant speed with equal intervals at different periods whereas object B has different intervals of time at different periods and hence travelling at varying speeds.
So it is clear that object A is in uniform motion and object B is in non-uniform motion.
Conclusion for uniform motion and non-uniform motion:
Uniform motion means when a body travels an equal distance in equal intervals of time. A few examples are hands of the watch, earth revolving and rotating around the sun, movement of blades of a fan etc.
Non-uniform motion means when a body travels unequal distances in equal intervals of time. A few examples are the motion of a vehicle or train, a person walking or jogging etc. The fast speed object covers the given distance in less time, while the slow speed object covers the given distance in more time.
If we were to represent uniform motion and non-uniform motion graphically, the curve would be a straight line, whereas in the case of a non-uniform motion, the curve on the graph would be a curved line.
Hence it is clear that to calculate the uniform and non-uniform motion, the speed is the underlying factor in the given time.