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