Willer Academy

Nation Builders Through Education | Founded by Er. Rahul Kumar Dubey Sir

Chapter 13: Motion and Time

Subject: Science (Physics)

Class: 7

Series: Base Builder for Moderate to Hard

Learning Objectives

By the end of this chapter, you, the future scientist and nation-builder, will be able to:

1. Understand different types of motion and their characteristics
2. Differentiate between speed and velocity
3. Calculate speed, distance, and time using mathematical formulas
4. Interpret distance-time graphs and understand their significance
5. Understand various units of time and their conversions
6. Solve numerical problems related to motion and time
7. Apply knowledge to real-life situations involving motion

13.1 Introduction: Understanding Motion

Motion is a change in the position of an object with respect to time. Everything in the universe is in motion, from electrons orbiting nuclei to galaxies moving through space.

Quick Check

Look around you and identify five objects in motion. What type of motion does each exhibit?

13.2 Types of Motion

Objects can move in different ways depending on their path and nature of movement.

Linear Motion

• Motion along a straight line
• Example: Car moving on a straight road
• Simplest type of motion
• Can be uniform or non-uniform

Circular Motion

• Motion along a circular path
• Example: Earth revolving around the Sun
• Direction changes continuously
• Accelerated motion

Periodic Motion

• Motion that repeats at regular intervals
• Example: Pendulum of a clock
• Time period remains constant
• Used in timekeeping devices

Numerical & Application 1: Calculating Speed

• Scenario: A car travels 240 km in 4 hours.
• Problem: What is the speed of the car? If the car continues at this speed, how far will it travel in 7 hours?
• Solution:
  • Speed = Distance/Time = 240 km / 4 h = 60 km/h
  • Distance = Speed × Time = 60 km/h × 7 h = 420 km

This shows the relationship between speed, distance, and time!

Experiment: Measuring Speed

Mark a distance of 50 meters in your school ground. Ask a friend to run this distance while you measure the time taken with a stopwatch. Calculate their speed in m/s and km/h.

13.3 Speed and Velocity

Speed is how fast an object is moving, while velocity is speed in a specific direction.

Aspect	Speed	Velocity
Definition	Distance traveled per unit time	Displacement per unit time
Quantity Type	Scalar (magnitude only)	Vector (magnitude and direction)
Formula	Speed = Distance/Time	Velocity = Displacement/Time
Example	60 km/h	60 km/h North

Task 1: Speed vs. Velocity

A car travels 60 km East and then 20 km West in 2 hours. Calculate its average speed and average velocity.

13.4 Measurement of Time

Time is measured using periodic motions that repeat at regular intervals. Throughout history, humans have used various devices to measure time.

Ancient Timekeeping

Sundials, water clocks, and hourglasses were used to measure time before mechanical clocks were invented.

Mechanical Clocks

Pendulum clocks use the regular swinging of a pendulum to measure time accurately.

Modern Timekeeping

Quartz crystals and atomic clocks provide extremely accurate time measurements.

Numerical & Application 2: Time Conversion

• Scenario: A movie has a duration of 2 hours 15 minutes.
• Problem: Express this time in minutes and seconds.
• Solution:
  • 2 hours = 2 × 60 = 120 minutes
  • Total minutes = 120 + 15 = 135 minutes
  • Total seconds = 135 × 60 = 8100 seconds

This shows how to convert between different units of time!

13.5 Distance-Time Graphs

Distance-time graphs show how the distance traveled by an object changes with time. The slope of the graph represents the speed of the object.

Interpreting Distance-Time Graphs

1h

2h

3h

4h

5h

40km

30km

20km

10km

0km

This graph shows varying speeds: increasing, constant, and decreasing

Experiment: Creating a Distance-Time Graph

Walk at different speeds (slow, normal, fast) for 1 minute each while a friend records the distance covered every 15 seconds. Plot these values on a graph with time on the x-axis and distance on the y-axis. Analyze the graph to determine when you were moving fastest.

13.6 Units and Measurements

Different units are used to measure distance, time, and speed depending on the context and country.

Common Units and Conversions

Distance

1 km = 1000 m

1 m = 100 cm

Time

1 hour = 60 minutes

1 minute = 60 seconds

Speed

1 m/s = 3.6 km/h

1 km/h = 5/18 m/s

Task 2: Unit Conversion

Convert a speed of 90 km/h to m/s. Then convert 15 m/s to km/h. Which is faster?

Section B: Multiple Choice Questions

Q1. Which of the following is an example of periodic motion?

• A. A car moving on a straight road
• B. A swing moving back and forth
• C. A ball falling vertically downward
• D. A bird flying in the sky

Q2. If a car travels 180 km in 3 hours, what is its speed?

• A. 45 km/h
• B. 60 km/h
• C. 90 km/h
• D. 540 km/h

Q3. What does the slope of a distance-time graph represent?

• A. Distance
• B. Time
• C. Speed
• D. Acceleration

Q4. Which of these is a unit of speed?

• A. Meter
• B. Second
• C. Meter/Second
• D. Meter/Second²

Q5. A straight horizontal line on a distance-time graph indicates:

• A. Uniform motion
• B. No motion
• C. Accelerated motion
• D. Decelerated motion

Section B: Multiple Choice Questions

Q6. Which of the following is an example of uniform motion?

• A. A car accelerating on a highway
• B. A train moving at a constant speed on a straight track
• C. A ball rolling down a hill
• D. A cyclist speeding up

Q7. Displacement differs from distance because:

• A. Displacement is always positive
• B. Displacement considers only magnitude
• C. Displacement considers direction
• D. Displacement is measured in meters squared

Q8. A car travels 50 km North and then 50 km South. Its displacement is:

• A. 100 km
• B. 50 km
• C. 0 km
• D. Cannot be determined

Q9. If the slope of a distance-time graph is zero, it means:

• A. Object is moving with uniform speed
• B. Object is at rest
• C. Object is accelerating
• D. Object is moving in circular motion

Q10. The SI unit of velocity is:

• A. m/s²
• B. km
• C. m/s
• D. s

Q11. Which motion is used in clocks for measuring time?

• A. Random motion
• B. Circular motion
• C. Periodic motion
• D. Linear motion

Q12. The distance covered by a car is 180 km in 3 hours. Its average speed is:

• A. 30 km/h
• B. 60 km/h
• C. 90 km/h
• D. 45 km/h

Q13. Which of these quantities is a vector?

• A. Speed
• B. Distance
• C. Velocity
• D. Time

Q14. A body covers equal distances in equal intervals of time. Its motion is called:

• A. Uniform motion
• B. Non-uniform motion
• C. Accelerated motion
• D. Retarded motion

Q15. A car moves 20 km East and then 30 km West. The total distance and displacement are respectively:

• A. 50 km, 10 km West
• B. 10 km, 50 km West
• C. 50 km, 20 km East
• D. 50 km, 30 km West

Q16. Which of the following is a non-uniform motion?

• A. A train moving at 60 km/h on a straight track
• B. A car slowing down while approaching a traffic signal
• C. A bird flying at constant speed in one direction
• D. A runner moving at steady speed on a track

Q17. A distance-time graph with a curved line indicates:

• A. Uniform speed
• B. Acceleration or deceleration
• C. Object at rest
• D. Constant displacement

Q18. Time measured by a pendulum clock is based on:

• A. Linear motion
• B. Random motion
• C. Periodic motion
• D. Circular motion

Q19. If a car travels 100 km in 2 hours and 50 km in 1 hour, its average speed is:

• A. 50 km/h
• B. 60 km/h
• C. 75 km/h
• D. 100 km/h

Q20. The SI unit of acceleration is:

• A. m/s
• B. m/s²
• C. km/h
• D. km/h²

Answer Key: Multiple Choice Questions

Q1: B. A swing moving back and forth

Q2: B. 60 km/h

Q3: C. Speed

Q4: C. Meter/Second

Q5: B. No motion

Q6: B. A train moving at a constant speed on a straight track

Q7: C. Displacement considers direction

Q8: C. 0 km

Q9: B. Object is at rest

Q10: C. m/s

Q11: C. Periodic motion

Q12: B. 60 km/h

Q13: C. Velocity

Q14: A. Uniform motion

Q15: A. 50 km, 10 km West

Q16: B. A car slowing down while approaching a traffic signal

Q17: B. Acceleration or deceleration

Q18: C. Periodic motion

Q19: B. 60 km/h

Q20: B. m/s²

Section C: Answer in Detail (For Answer Writing Practice)

Q1. Explain the difference between speed and velocity with examples. Why is velocity considered a vector quantity while speed is a scalar quantity?

Hint: Include definitions, examples, and the importance of direction.

Q2. Describe the various types of motion with suitable examples. Draw diagrams to illustrate each type.

Hint: Include linear, circular, periodic, and random motion with daily life examples.

Q3. How can you determine the speed of an object from its distance-time graph? Explain with the help of a diagram.

Hint: Include how to calculate slope and interpret different graph shapes.

Section D: Tackle These! (Higher Order Thinking Skills - HOTS)

Q1. Two friends start from the same point and walk in opposite directions. One walks at 4 km/h and the other at 5 km/h. What will be the distance between them after 2 hours? If they walked in the same direction, what would the distance be?

Think about: Relative speed in same and opposite directions.

Q2. Analyze the distance-time graph of an object that starts from rest, moves with constant speed, then stops for some time, and finally returns to its starting point. Draw the graph and explain each section.

Think about: How different motions are represented on the graph.

Q3. Design an experiment to measure the average speed of a student running in the playground. What instruments would you use? How would you ensure accuracy in your measurements?

Think about: Measurement tools, procedures, and calculations.

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"Time and tide wait for no one, but understanding motion helps us make the most of both." - Keep learning, keep growing.

Er. Rahul Kumar Dubey Sir

Willer Academy - Building a Stronger Nation, One Student at a Time.