Class 7 Science

Motion

When an object changes its position with elapse of time in respect to a stationary object, such as a building, electric pole, etc., the object is said to be in motion.

Slow and Fast Motion: If an object ‘A’ covers a distance in less time and another object covers the same distance in more time, the object A is called a faster moving object and object B is called a slower moving object. In other words, object A has faster motion and object B has slower motion.


Types of Motion

Rectilinear Motion: Motion along a straight line is known as RECTILINEAR MOTION OR MOTION ALONG A STRAIGHT LINE. For example: Motion of a car along a straight line.

Curvilinear Motion: Motion along a curve line is known as CURVILINEAR MOTION. For example: Motion of car or any moving object along a curve line.

Circular Motion: Motion along a circle is known as CIRCULAR MOTION. For example: Motion of cyclist along a circular park.



Speed

Speed: Distance covered by an object in unit time is called speed.

Speed = Distance/Time

Speed may be divided into three types: Uniform speed, Non-Uniform Speed and Average Speed

Uniform Speed: If an object covers a fixed distance in each unit of time the motion is known as UNIFORM MOTION or UNIFORM SPEED.

Non-uniform Speed: If an object does not cover a fixed distance in each unit of time the motion is known as NON-UNIFORM MOTION or NON-UNIFORM SPEED.

Average Speed: Total distance covered divided by total time taken is known as AVERAGE SPEED.

Average Speed = Total Distance Covered/Total time taken

Speed is also known as VELOCITY.



Review Question:

Question 1: A car covers a distance of 100 km in 5 hour, calculate its speed.

Answer: Given, Total distance = 100 km
Total time taken = 5 hour
We know that
Average Speed = Distance ÷ time
= 100 km ÷ 5 hour = 20 km per hour

Question 2: A car covers 20 km in the first hour and cover 30 km in the last 4 hours. Find its average speed.

Answer: Given, Total distance covered = 20 km + 30 km = 50 km
Total time taken = 1 hour + 4 hour = 5 hour
We know that,
Average Speed = Distance/time
= 50 ÷ 5 = 10 km per hour