[Physics Class Notes] on Unit of Speed Pdf for Exam

You might come across the term ‘speed’ almost every day, no matter to which walk of life you belong to. Yet, what does ‘speed’ actually mean in terms of physics? Is it any different from the sense you generally use it in? Moreover, what is the SI unit of speed? This article will help you answer all the questions that you have in mind regarding this topic. 

In the field of physics, speed refers to the rate at which an object moves. More specifically, this term implies the distance that an object travels with respect to time. You witness moving objects daily, such as a car, a cycle, or even while walking. Thus, speed is the measurement of the distance that a body covers within a particular time. 

When a body covers greater distance within a specific amount of time, you can say that it has a high speed. On the other hand, when that very body covers a short distance at the same time, the speed is low. 

Calculating Average Speed

Average speed can be calculated by dividing the total distance the object travels by the total amount of time it takes to travel that distance.

While the speed of the object may vary during the total time it is moving, the average speed is the result of the total distance divided by the total time taken.

Speed measurements contain a unit of distance divided by a unit of time. Examples of units of speed might include “meters per second” (m/s), “kilometers per hour” (km/h), or “miles per hour” (mph or mi/hr).

Average speed can be calculated using the formula v=d/t where the variables are:

v is the average speed of the object with units of m/s

d is the total distance or length of the path of the object with units of m

t is the total time taken to cover the path with units of s

Speed cannot have a negative value.

Velocity (Speed and Direction)

Velocity refers to both the speed of an object and the direction of its motion.

A velocity value should have both speed units and direction units, such as m/sec north, km/h south, cm/s left, or km/min down.

If an object is moving forward, it has positive velocity. When an object is moving backwards, it has negative velocity.

When you throw a ball in the air, it has positive velocity. When it heads back towards you, it has negative velocity.

 

What is the SI Unit of Speed? 

Every measurement requires an SI unit so that it becomes easy to distinguish it from the rest. A simple numerical expression is ambiguous and vague, and it could mean a thousand things. Therefore, you will need a basic unit of speed that differentiates it from other measurements. 

Now, if you are asking what the basic unit of speed is, here is the answer – 

Meter per second is the SI unit of speed. This unit of speed signifies as to how many meters an object can travel within a second. Say, a body travels 10 meters in a second. In that case, the speed of the body is 10 meters per second. 

The SI unit of speed is written as m/s.

What is the Derivation of the SI Unit of Speed? 

Now that you know that speed is the distance that an object travels within a specific time, you must also note why the unit of speed is a derived unit. 

The definition of speed in mathematical terms is expressed by the following formula which is also used to calculate the same. 

ν = d/t

Where ” V stands for speed, ‘d’ means distance, and ‘t’ implies time. 

Suppose that an object covers 50 meters at a time of 5 seconds, then – 

ν = 50 metres/ 5 seconds = 10 meters/second or 10 m/s. Therefore, the SI unit of speed is 10 m/s for this object. 

Also, speed also possesses a dimensional formula, which is M0.L1.T-1.

You can also express the SI unit of speed in terms of the CGS system, or centimeter-gram-second system. In that case, cm/s or cm s-1 signifies the speed of a moving object. 

Wondering How to Convert m/s into cm/s or the CGS Unit of Speed? 

Suppose that an object moves 100 meters in 20 seconds. Consequently, the speed becomes 5 m/s. However for CGS unit, you will have to convert 100 meters into cms. 

1 m = 100 cm

Therefore, 100 m = 100 X 100 cm = 10,000 cm. Thus, the CGS expression of speed in this case becomes-

ν = 10,000 cm/20 seconds = 500 cm/s or 500 cm s-1. 

How to Calculate Speed?

Step 1: Place the constant velocity car in position on a surface, with plenty of space in front of it. Use the duct tape to mark the starting position of the car, placing a piece right behind the back wheels.

Step 2: Measure a distance from the tape, a few meters along the floor (longer is better), and place a second piece of duct tape. Note down the total distance.

Step 3: Turn on the motorized car, place it in position in front of the starting tape, and release it, starting the stopwatch at the same time.

Step 4: Stop the stopwatch when it reaches the second piece of tape, and note down the time in a data table that looks something like this:

Step 5: Repeat the experiment at least five times, and note down all the trials.

Step 6: Find the average of your five or more trials by adding up the numbers and dividing by how many trials you did.

Step 7: Calculate the speed of your car using the equation: speed equals distance divided by time.

Some Interesting Facts Related to Speed 

Keep in mind the following interesting facts involving speed – 

• The speed at which light travels is 299,792,458 m/s. 

• The speed of sound in dry air is 343.20 m/s. 

• You would have to travel at a speed of 11.2 km/s (or 11200 m/s) to escape the gravitational pull of our planet. 

Now that you know that the SI unit of speed is m/s, browse our website to learn even more about the intriguing properties of speed and other related concepts.

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