You will be amazed to know that the speed of the rocket, that is used to launch a satellite into earth�s orbit is about 8 km/sec. Wow ! so fast !! On the other hand, a tortoise can move only at a speed of 8 cm/sec. Now can you imagine the differences in the speed of a rocket and a tortoise? The rocket moves almost 100 thousand times faster than a tortoise. Let us learn how to calculate time speed and distance.

 

Once you know the speed of an object, you can very easily find the distance covered by the moving object in a given time.

 

To find the distance, you simply multiply the speed by time.

 

Hence, Distance covered = speed x time.

 

or you can say the relation between time speed and distance is distance covered = speed x time.

 

For example, if the speed of a train is 85km/hr, the distance moved by train in 3 hours will be

 

= 85km/hr x 3 hr = 255 km

 

We can also find the time, a moving object would take to cover a given distance if the speed of the moving object is known.

 

Time taken = distance /speed.

 

For example, if the average speed of a bus is 60km/hr, how much time the bus will take to cover a distance of 150 km?

 

The time taken will be
Time taken = 150km/60km/hr = 2.5 hrs.

 

Hence using the formulae of speed, we can find either the speed, time taken or the distance travelled by a body, given the other two parameters of the formulae.

 

Unit of time and speed

 

Let us learn the Si units of time speed and distance. We often measure time in days, hours, minutes, or seconds. But the basic unit of time is second its symbol is 's'. Similarly, the basic unit of distance is the meter and its symbol is �m�.

 

What would be the basic unit of speed?

 

As we know that the speed is equal to distance upon a time. The basic unit of speed will be meter upon second or meter per second or �m�/�s�.

 

Speed, however, can be expressed in other units such as meters per minute or kilometers per hour. Generally, speed is expressed in Kilometer per hour. It is important to remember that symbols of all units are written in the singular. For example, we write 50 km and not 50 kms.

 

Though the basic unit of time is second, we also use other units of time such as minute, hour, day, year, etc. depending on the need.

 

For example, The age of a person is expressed in years rather than in days and hours. Daily duty times of employees are expressed in hours, not in minutes or seconds. The time taken to prepare tea is measured in minutes.

 

Speedometer and Odometer

 

Let us learn about speedometer and odometer in this blog on time speed and distance. You must have seen a dial around the steering of the bus driver or in your car or scooter. All the buses, cars, scooters, and motorcycles are fitted with dials called speedometers and odometers.

 

A speedometer is a device that measures and displays the instantaneous speed of a land vehicle. It indicates the speed of a vehicle in miles per hour or kilometers per hour or both. The device uses a needle to point to a specific speed. A speedometer is often fitted on the top of a scooter or a motorcycle. In cars, speedometers are fitted on the dashboards.

 

Another meter called an odometer is also fitted on cars, scooters, and motorcycles. An odometer is an instrument that indicates the distance traveled by a vehicle.

 

Distance Time Graph

 

To describe the motion of an object, we can use the line graph. A graph is plotted between two variable quantities The quantity which we can change according to our own choice is called an independent variable and the quantity which depends on the value of the independent quantity is called the dependent variable. E.g. in the distance-time graph, time is an independent variable and distance is a dependent variable

 

Generally, Independent variables are represented along the x-axis and dependent variables are represented along the y-axis. Now let us discuss the Distance- Time Graph. The distance-time graph represents the change in position of a body with respect to time. In this graph, we have taken time along the x-axis and the distance along the y-axis.

 

Suppose the distance traveled by a car at regular intervals is-

 

The car is traveling equal distances in equal intervals of time. This means that car is moving at a uniform speed. We plot the points for various pairs of corresponding values of the two variables and join these points by a free-hand curve to obtain a graph. This is the distance-time graph representing a body with uniform motion

 

We can use the distance-time graph to determine the speed of an object. Now to find the speed of an object from the distance-time graph, consider a small part AB of the distance-time graph. From both points A and B, draw lines perpendicular to the x-axis and y-axis. Let the distance traveled by the body, corresponding to point A, in time t1 is s1 and the distance traveled by the body, corresponding to the point B, in time t2 is s2

 

As we know that Speed= distance travelled/ time taken
Therefore, V = (s2-s1)/(t2-t1)

 

Read More: Newton's First Law of Motion: Definition, Inertia, and Examples