Class 7 Science

Chapter 13: Motion and Time

STAGE 0: Foundation / Basics

When an object changes its position with time, it is said to be in motion.

To measure motion, we need to measure time.

Motion

An object is said to be in motion if it changes its position with respect to a fixed point.

Examples:

• A moving car
• A running child
• Flowing river

Types of Motion

• Rectilinear motion – motion in a straight line
• Circular motion – motion in a circular path
• Periodic motion – motion repeated at regular intervals

Speed

Speed tells us how fast an object is moving.

Speed = Distance ÷ Time

The SI unit of speed is metre per second (m/s).

Measurement of Time

Time is measured using:

• Clock
• Watch
• Stopwatch

Distance–Time Graph

A distance–time graph shows the motion of an object.

• Straight line → uniform motion
• Curved line → non-uniform motion

STAGE 2: NCERT Textbook Questions & Answers

Q1. What is motion?

Motion is the change in position of an object with time.

Q2. Define speed.

Speed is the distance travelled per unit time.

Q3. Write the formula for speed.

Speed = Distance ÷ Time

STAGE 3: Exam-Oriented Questions

Fill in the blanks:

• The SI unit of speed is __________.
• Motion repeated at equal intervals is called __________ motion.

Very Short Answer:

Name one instrument used to measure time.
Answer: Stopwatch

Quick Revision Points

• Motion means change in position
• Speed tells how fast an object moves
• Speed = Distance ÷ Time
• Graphs help understand motion