Motion and Time Class 7 CBSE Science Notes - Complete Guide with Solutions

Motion and Time for Class 7 Students

Understanding motion and time is fundamental to grasping how the physical world operates around us. From the flight of birds to the movement of planets, everything in the universe exhibits some form of motion. This comprehensive guide covers the complete Motion and Time chapter for Class 7 CBSE Science, including key concepts, formulas, solved examples, and practice questions with answers.

Whether you're preparing for your exams or looking to strengthen your conceptual understanding, these motion and time class 7 notes will serve as your complete resource. We'll explore different types of motion, understand the relationship between speed, velocity, and acceleration, and master the equations of motion through detailed explanations and examples.

What is Motion? Understanding Rest and Motion

In our everyday observations, we notice objects in two fundamental states: at rest or in motion. Understanding the difference between these states is the foundation of studying motion.

Definition of Rest

A body is said to be at rest when it does not change its position with respect to a fixed point in its surroundings.

Example: A book lying undisturbed on a table maintains its position relative to the table and is therefore in a state of rest.

Definition of Motion

A body is said to be in motion when it changes its position with respect to a fixed point or object in its surroundings.

Examples:

• A flying bird changing its position in the sky
• A moving bus traveling along a road
• A sailing ship crossing the ocean
• A walking person moving from one place to another
• A pendulum of a wall clock oscillating about its lowest point

Important Concept: Motion is relative. An object may be at rest with respect to one reference point but in motion with respect to another. This is why we always specify motion or rest "with respect to" a particular reference point.

Types of Motion - Classification and Examples

Motion can be classified into several distinct categories based on the path and manner of movement. Understanding these classifications helps in analyzing real-world motion scenarios.

1. Translatory Motion

Definition: Motion in which all points of a moving body move uniformly in the same line or direction, covering the same distance at the same time.

Translatory motion is further divided into two types:

(a) Rectilinear Motion (Linear Motion)

Definition: When an object moves along a straight line, its motion is called rectilinear motion.

Examples:

• A car moving on a straight road
• A freely falling body toward the Earth's surface
• A train moving on straight tracks

(b) Curvilinear Motion

Definition: When an object moves along a curved or circular path, its motion is called curvilinear motion.

Examples:

• A car navigating a curved road
• A javelin thrown by an athlete following a parabolic path
• An arrow shot from a bow

Special Case - Circular Motion: The movement of a body along a circular path is called circular motion. It is a special type of curvilinear motion.

Example: A stone whirling when tied to a string

2. Rotatory Motion

Definition: A body exhibits rotatory motion when it moves about a fixed axis without changing the radius of its motion.

Examples:

• The blades of a ceiling fan rotating about the central axis
• A spinning top rotating on its pointed end
• The wheels of a moving bicycle

3. Oscillatory Motion

Definition: The to-and-fro motion of an object along the same path about its mean position is called oscillatory motion.

Examples:

• The motion of a pendulum in a wall clock
• The motion of a swing in a playground
• The piston of an engine moving back and forth

4. Vibratory Motion

Definition: A type of oscillatory motion where a certain part of the body remains fixed while the rest moves to and fro in a particular manner about its mean position.

Examples:

• The expansion and contraction of our chest during breathing
• The vibration of guitar strings when plucked
• The movement of a tuning fork when struck

5. Periodic Motion

Definition: Motion that repeats itself after regular intervals of time is called periodic motion.

Examples:

• The swinging pendulum of a wall clock
• The revolution of Earth around the Sun (one complete revolution per year)
• The rotation of Earth on its axis (one complete rotation per day)

6. Non-Periodic Motion

Definition: Motion that does not repeat itself after regular intervals of time is called non-periodic motion.

Examples:

• A footballer running on a field
• The motion of ocean tides
• A person walking in a park

7. Multiple Motion

Definition: When a moving object performs two or more types of motions simultaneously, it is called multiple motion.

Examples:

• A person drawing water from a well (combination of circular motion of the handle and translatory motion of the bucket)
• A rider on a bicycle (the rider moves in translatory motion while the wheels undergo both rotatory and translatory motion)

8. Rolling Motion

Definition: Motion in which a body undergoes both translatory and rotatory motion simultaneously is called rolling motion.

Examples:

• A cylinder rolling down an inclined plane
• The movement of a drill bit
• A ball rolling on the ground

9. Random Motion

Definition: When an object in motion has no specific path and suddenly changes its direction of motion, it exhibits random motion.

Examples:

• Motion of a football on the ground during a game
• A flying kite that may have translatory motion at one instant and rotatory motion the next moment
• The movement of gas molecules in a container

Uniform and Non-Uniform Motion

Understanding the uniformity of motion helps us predict and analyze the behavior of moving objects.

Uniform Motion

Definition: When an object covers equal distances in equal intervals of time, it is said to be in uniform motion.

Characteristics:

• The distance covered per unit time remains constant
• The speed of the object remains constant
• The time intervals considered should be small

Example: A train moving straight in a particular direction at a constant speed of 60 km/h covers 60 km every hour consistently.

Detailed Illustration: Consider an object moving along a straight line. If it travels 5 meters in the first second, 5 meters in the second second, 5 meters in the third second, and 5 meters in the fourth second, the object is in uniform motion because it covers equal distances (5 m) in equal time intervals (1 second each).

Non-Uniform Motion

Definition: When an object covers unequal distances in equal intervals of time, it is said to be in non-uniform motion.

Characteristics:

• The distance covered per unit time changes
• The speed of the object varies
• The motion is irregular or variable

Examples:

• A car moving on a crowded street (speeds up, slows down, stops)
• A person jogging in a park (varying pace)
• A ball rolling down a slope (increasing speed)

Scalar and Vector Quantities

Physical quantities can be classified based on whether they have only magnitude or both magnitude and direction.

Scalar Quantity

Definition: Physical quantities that have only magnitude but no specific direction are called scalar quantities.

Characteristics:

• Represented by a single numerical value
• Can be added or subtracted using ordinary arithmetic
• Do not require directional specification

Examples:

• Length (10 meters)
• Mass (5 kilograms)
• Area (25 square meters)
• Distance (100 kilometers)
• Time (30 seconds)
• Temperature (25°C)
• Speed (50 km/h)

Vector Quantity

Definition: Physical quantities that have both magnitude and direction are called vector quantities.

Characteristics:

• Represented by magnitude and direction
• Require special methods for addition and subtraction
• Direction is essential for complete description

Examples:

• Velocity (50 km/h toward north)
• Acceleration (10 m/s² downward)
• Force (100 N eastward)
• Displacement (15 meters west)
• Weight (600 N downward)

Distance and Displacement - Main Differences

Understanding the distinction between distance and displacement is crucial for solving motion problems.

Distance

Definition: The total path covered by any object is called its distance. It is a scalar quantity.

Characteristics:

• Always positive
• Depends on the actual path taken
• Measured along the path of motion
• SI Unit: meter (m)
• Other units: centimeter (cm), kilometer (km)

Unit Conversions:

• 1 kilometer = 1000 meters
• 1 meter = 100 centimeters

Example: If an object moves from point A to B through 6 meters and then from B to C through 8 meters, the total distance traveled is:

Distance = AB + BC = 6 + 8 = 14 meters

Displacement

Definition: The shortest path covered by any object is called its displacement. It is a vector quantity.

Characteristics:

• Can be positive, negative, or zero
• Independent of the path taken
• Measured as the straight-line distance from initial to final position
• SI Unit: meter (m)
• Other units: centimeter (cm), kilometer (km)

Example: If an object moves from A to B, 4 kilometers due west, and then from B to C, 3 kilometers due north, the displacement is the straight-line distance from A to C.

Using the Pythagorean theorem: Displacement = √(4² + 3²) = √(16 + 9) = √25 = 5 kilometers

Main Point: Displacement has direction (in this example, northwest from the starting point).

Important Relationship

For any given motion:

• Displacement ≤ Distance
• Displacement = Distance (only when motion is in a straight line without change in direction)
• Displacement < Distance (in all other cases)

Speed - The Rate of Motion

Speed is a fundamental concept that quantifies how fast an object is moving.

Definition of Speed

Speed gives us an idea about how fast a body is moving. It is the distance traveled by a body per unit time.

Formula:

Speed = Distance traveled / Time taken
s = d / t

Characteristics:

• Speed is a scalar quantity (has magnitude only)
• Always positive or zero
• SI Unit: meter per second (m/s)
• Other common units: kilometer per hour (km/h), centimeter per second (cm/s)

Understanding Speed Through Comparison

When comparing the motion of a bicycle and a car on the road, we observe that the car travels a greater distance in the same time period. Therefore, we say the car moves faster than the bicycle. This comparison is made possible through the concept of speed.

Unit Conversion for Speed

A commonly used conversion in problems:

Converting km/h to m/s:

Speed in m/s = Speed in km/h × (5/18)

Converting m/s to km/h:

Speed in km/h = Speed in m/s × (18/5)

Example: 72 km/h = 72 × (5/18) = 20 m/s

Velocity - Speed with Direction

Velocity extends the concept of speed by incorporating direction, making it a more complete description of motion.

Definition of Velocity

Velocity gives us an idea about the motion of a body along with its direction. It is the displacement of a body per unit time.

Formula:

Velocity = Displacement / Time
v = s / t

Characteristics:

• Velocity is a vector quantity (has both magnitude and direction)
• Can be positive, negative, or zero
• SI Unit: meter per second (m/s)
• Direction must be specified (north, south, east, west, up, down, etc.)

Difference Between Speed and Velocity

Important Example: A car traveling around a circular track at constant speed has changing velocity because its direction continuously changes, even though its speed remains constant.

Acceleration - The Rate of Change of Velocity

Acceleration describes how quickly the velocity of an object changes over time.

Definition of Acceleration

Acceleration is defined as the rate of change of velocity of a body.

When a car starts from rest, it gradually attains a certain velocity. When the driver wants to slow down, the velocity decreases until it becomes zero. These changes in velocity are expressed through acceleration.

Formula:

Acceleration = Change in velocity / Time
Acceleration = (Final velocity - Initial velocity) / Time
a = (v - u) / t

Where:

• a = acceleration
• v = final velocity
• u = initial velocity
• t = time taken

Characteristics:

• Acceleration is a vector quantity
• SI Unit: meter per second squared (m/s²)
• Can be positive (speeding up), negative (slowing down), or zero (constant velocity)

Types of Acceleration

Positive Acceleration: When the velocity of an object increases with time

• Example: A car starting from rest and speeding up

Negative Acceleration (Retardation/Deceleration): When the velocity of an object decreases with time

• Example: A car applying brakes and slowing down

Zero Acceleration: When the velocity of an object remains constant

• Example: A car moving at constant speed in a straight line

Equations of Motion - Mathematical Framework

The equations of motion provide mathematical relationships between displacement, velocity, acceleration, and time for uniformly accelerated motion.

The Three Equations of Motion

These equations apply when acceleration is constant (uniform):

First Equation of Motion:

v = u + at

This equation relates final velocity, initial velocity, acceleration, and time.

Second Equation of Motion:

s = ut + (1/2)at²

This equation relates displacement, initial velocity, time, and acceleration.

Third Equation of Motion:

v² = u² + 2as

This equation relates final velocity, initial velocity, acceleration, and displacement (without time).

Symbols and Their Meanings

• u = Initial velocity (velocity at the start)
• v = Final velocity (velocity at the end)
• a = Acceleration (rate of change of velocity)
• t = Time (duration of motion)
• s = Displacement (shortest distance covered)

Formula Table

Unit Conversions

Solved Examples with Step-by-Step Solutions

Example 1: Calculating Distance from Speed and Time

Problem: Salma takes 5 minutes to travel from her house to her school on a bicycle. If the bicycle has a speed of 2 m/s, calculate the distance between her house and the school.

Solution:

Given:

• Time taken (t) = 5 minutes = 5 × 60 seconds = 300 seconds
• Speed (s) = 2 m/s
• Distance (d) = ?

Using the formula: Speed = Distance/Time

Rearranging: Distance = Speed × Time

Distance = 2 m/s × 300 s = 600 meters

Answer: The distance between Salma's house and school is 600 meters.

Example 2: Calculating Speed from Distance and Time

Problem: The distance between two stations is 240 km. A train takes 4 hours to cover this distance. Calculate the speed of the train.

Solution:

Given:

• Distance (d) = 240 km
• Time taken (t) = 4 hours
• Speed (s) = ?

Using the formula: Speed = Distance/Time

Speed = 240 km / 4 hours = 60 km/h

Answer: The speed of the train is 60 km/h.

Example 3: Calculating Final Velocity Using First Equation of Motion

Problem: A motorbike is moving with a velocity of 8 m/s. It is accelerated at a rate of 0.8 m/s² for 20 seconds. Find the velocity of the motorbike after 20 seconds.

Solution:

Given:

• Initial velocity (u) = 8 m/s
• Acceleration (a) = 0.8 m/s²
• Time (t) = 20 seconds
• Final velocity (v) = ?

Using the first equation of motion: v = u + at

Substituting the values: v = 8 + (0.8 × 20) v = 8 + 16 v = 24 m/s

Answer: The velocity of the motorbike after 20 seconds is 24 m/s.

Example 4: Finding Velocity When Starting from Rest

Problem: A car starts from rest and is accelerated at the rate of 3 m/s² for 8 seconds. Find the velocity of the car at the end of 8 seconds.

Solution:

Given:

• Initial velocity (u) = 0 m/s (starts from rest)
• Acceleration (a) = 3 m/s²
• Time (t) = 8 seconds
• Final velocity (v) = ?

Using the first equation of motion: v = u + at

Substituting the values: v = 0 + (3 × 8) v = 0 + 24 v = 24 m/s

Answer: The velocity of the car at the end of 8 seconds is 24 m/s.

Motion and Time Class 7 Extra Questions with Answers

Objective Type Questions (MCQs)

1. A body whose position with respect to surroundings does not change is said to be in a state of:

A. Rest
B. Motion
C. Vibration
D. Oscillation

Answer: A. Rest

2. In the case of a moving body:

A. Displacement > Distance
B. Displacement ≤ Distance
C. Displacement = Distance
D. Distance < Displacement

Answer: B. Displacement ≤ Distance

3. Vector quantities are those which have:

A. Only direction
B. Only magnitude
C. Magnitude and direction
D. None of these

Answer: C. Magnitude and direction

4. What is true about scalar quantities?

A. Scalar quantities have direction also
B. Scalars can be added arithmetically
C. There are special laws for scalar addition
D. Scalars have special method to represent

Answer: B. Scalars can be added arithmetically

5. A body is said to be in motion if:

A. Its position with respect to surrounding objects remains same
B. Its position with respect to surrounding objects keeps on changing
C. Both (A) and (B)
D. Neither (A) nor (B)

Answer: B. Its position with respect to surrounding objects keeps on changing

6. Distance is always:

A. Shortest length between two points
B. Path covered by an object between two points
C. Product of length and time
D. None of the above

Answer: B. Path covered by an object between two points

7. Displacement:

A. Is always positive
B. Is always negative
C. Either positive or negative
D. Neither positive nor negative

Answer: C. Either positive or negative

8. Examples of vector quantities are:

A. Velocity, length, and mass
B. Speed, length and mass
C. Time, displacement and mass
D. Velocity, displacement and force

Answer: D. Velocity, displacement and force

9. Which of the following is NOT a characteristic of displacement?

A. It is always positive
B. It has both magnitude and direction
C. It can be zero
D. Its magnitude is less than or equal to the actual path length

Answer: A. It is always positive

10. The conversion factor for km/h to m/s is:

A. 5/18
B. 5/36
C. 5/54
D. 5/324

Answer: A. 5/18

11. When a body covers equal distance in equal intervals of time, its motion is said to be:

A. Non-uniform
B. Uniform
C. Accelerated
D. Back and forth

Answer: B. Uniform

12. The motion along a straight line is called:

A. Vibratory
B. Stationary
C. Circular
D. Linear

Answer: D. Linear

13. The motion of a body covering different distances in the same intervals of time is said to be:

A. Zig-Zag
B. Fast
C. Slow
D. Variable

Answer: D. Variable

14. The SI unit of velocity is:

A. m/s
B. km/s
C. cm/s
D. mm/s

Answer: A. m/s

15. Weight is a ________ quantity.

A. Scalar
B. Vector
C. Both (A) and (B)
D. Neither

Answer: B. Vector

16. The brakes applied to a car produce a negative acceleration of 6 m/s². If the car stops after 2 seconds, the initial velocity of the car is:

A. 6 m/s
B. 12 m/s
C. 24 m/s
D. Zero

Answer: B. 12 m/s

Solution: Using v = u + at
0 = u + (-6)(2)
0 = u - 12
u = 12 m/s

17. A body is moving along a straight line at 20 m/s and undergoes an acceleration of 4 m/s². After 2 seconds, its speed will be:

A. 8 m/s
B. 12 m/s
C. 16 m/s
D. 28 m/s

Answer: D. 28 m/s

Solution: Using v = u + at
v = 20 + (4)(2)
v = 20 + 8 = 28 m/s

18. When the distance traveled by an object is directly proportional to time, it is said to travel with:

A. Zero velocity
B. Constant speed
C. Constant velocity
D. Uniform velocity

Answer: B. Constant speed

19. The motion of a pendulum is:

A. Rotatory
B. Oscillatory
C. Curvilinear
D. Linear

Answer: B. Oscillatory

20. A bus changes its velocity from 2 m/s to 10 m/s at a rate of 8 m/s². How much time is required?

A. 1 sec
B. 2 sec
C. 8 sec
D. 5 sec

Answer: A. 1 sec

Solution: Using a = (v - u)/t
8 = (10 - 2)/t
8 = 8/t
t = 1 second

Motion and Time Class 7 Questions with Answers (Subjective)

Short Answer Questions

1. Distinguish between Distance and Displacement.

Answer:

2. State any three types of motion with examples.

Answer:

a) Translatory Motion: Motion in which all points of a body move uniformly in the same direction through the same distance.

• Example: A car moving on a straight road

b) Rotatory Motion: Motion of a body about a fixed axis without changing the radius.

• Example: Blades of a ceiling fan

c) Oscillatory Motion: To-and-fro motion of an object along the same path about its mean position.

• Example: Pendulum of a wall clock

3. Define scalar quantity. Give two examples.

Answer:

Scalar quantities are physical quantities that have only magnitude but no specific direction.

Examples:

1. Distance: The total path length covered (e.g., 100 meters)
2. Mass: The amount of matter in an object (e.g., 5 kilograms)

4. Define vector quantity. Give two examples.

Answer:

Vector quantities are physical quantities that have both magnitude and direction.

Examples:

1. Velocity: Speed in a specific direction (e.g., 50 m/s northward)
2. Force: Push or pull in a particular direction (e.g., 100 N downward)

5. Give any two examples to explain that motion is relative.

Answer:

Example 1: A passenger sitting in a moving train is at rest with respect to other passengers in the train, but is in motion with respect to trees and buildings outside the train.

Example 2: The Moon is in motion with respect to the Earth (orbiting around it), but appears stationary with respect to the stars when observed from Earth at a given instant.

This demonstrates that motion depends on the reference point chosen for observation.

6. A person moves in a circular path centered at origin O with radius 1 m. He starts from point A and reaches the diametrically opposite point B. Find:(i) Distance between A and B(ii) Magnitude of displacement between A and B

Answer:

Given:

• Radius of circular path = 1 m
• Movement from A to B (diametrically opposite points)

(i) Distance between A and B:

Distance is the actual path traveled = Half the circumference of the circle

Distance = πr = π × 1 = π meters ≈ 3.14 meters

(ii) Magnitude of displacement between A and B:

Displacement is the shortest distance = Diameter of the circle

Displacement = 2r = 2 × 1 = 2 meters

Note: The displacement is the straight-line distance from A to B, which is the diameter.

7. Write the difference between speed and velocity.

Answer:

8. A car is moving at a speed of 50 m/s. After 2 seconds, it is moving at 60 m/s. Calculate the acceleration of the car.

Answer:

Given:

• Initial velocity (u) = 50 m/s
• Final velocity (v) = 60 m/s
• Time (t) = 2 seconds
• Acceleration (a) = ?

Using the formula: a = (v - u)/t

a = (60 - 50)/2 a = 10/2 a = 5 m/s²

Answer: The acceleration of the car is 5 m/s².

9. A runner starting from rest accelerates at the rate of 0.5 m/s² for 20 seconds. What is the velocity achieved by him?

Answer:

Given:

• Initial velocity (u) = 0 m/s (starting from rest)
• Acceleration (a) = 0.5 m/s²
• Time (t) = 20 seconds
• Final velocity (v) = ?

Using the first equation of motion: v = u + at

v = 0 + (0.5 × 20) v = 0 + 10 v = 10 m/s

Answer: The velocity achieved by the runner is 10 m/s.

10. What is translatory motion? Name two kinds of translatory motions.

Answer:

Translatory Motion: It is the motion in which all points of a moving body move uniformly in the same line or direction, covering the same distance at the same time.

Two kinds of translatory motions:

1. Rectilinear Motion (Linear Motion):

• Motion along a straight line
• Example: A car moving on a straight highway

2. Curvilinear Motion:

• Motion along a curved path
• Example: A stone thrown at an angle following a parabolic path

Time and Motion Study - Understanding the Relationship

Time and motion study is a systematic observation technique used to establish standards and improve efficiency. While this concept is more commonly associated with industrial engineering and workplace efficiency, understanding the fundamental relationship between time and motion is essential in physics.

Main Principles:

1. Time Measurement in Motion:

• Motion is always measured with respect to time
• Without a time reference, we cannot determine speed, velocity, or acceleration
• Standard units of time (seconds, minutes, hours) allow consistent measurements

2. Analyzing Motion Over Time:

• Uniform motion shows equal distances covered in equal time intervals
• Non-uniform motion shows varying distances in equal time intervals
• Graphs (distance-time, velocity-time) help visualize these relationships

3. Practical Applications:

• Determining the most efficient routes for transportation
• Calculating travel times for journey planning
• Analyzing athletic performance
• Understanding planetary motion and celestial mechanics

Tips for Class 7 Students Studying Motion and Time

Study Strategies:

1. Master the Fundamentals:

• Clearly understand the difference between scalar and vector quantities
• Distinguish between distance and displacement
• Know when to use speed versus velocity

2. Memorize Key Formulas:

• Write formulas on flashcards
• Practice deriving one equation from another
• Understand what each symbol represents

3. Practice Problem-Solving:

• Start with simple numerical problems
• Gradually move to complex multi-step problems
• Always write down given values and required values
• Show all steps in your solution

4. Use Real-World Examples:

• Relate concepts to everyday observations
• Analyze the motion of vehicles, balls, and other objects around you
• This makes abstract concepts concrete and memorable

5. Create Visual Aids:

• Draw diagrams for different types of motion
• Make charts comparing related concepts
• Use graphs to understand distance-time and velocity-time relationships

Common Mistakes to Avoid:

1. Confusing distance with displacement - Remember, displacement is the shortest path
2. Mixing up speed and velocity - Velocity requires direction
3. Forgetting units - Always include appropriate units in your answers
4. Sign errors in acceleration - Negative acceleration means slowing down
5. Not converting units - Ensure all quantities are in the same unit system before calculation

Practice Questions for Self-Assessment

Additional Practice Problems:

Question 1: An athlete runs 400 meters in 50 seconds. Calculate his speed.

Question 2: A car travels at 60 km/h for 2 hours, then at 80 km/h for 3 hours. Calculate:

• (a) Total distance traveled
• (b) Average speed

Question 3: A body starting from rest moves with an acceleration of 2 m/s² for 10 seconds. Find:

• (a) Final velocity
• (b) Distance covered

Question 4: Differentiate between periodic and non-periodic motion with suitable examples.

Question 5: A ball is thrown vertically upward with a velocity of 20 m/s. Taking g = 10 m/s², calculate:

• (a) Maximum height reached
• (b) Time taken to reach maximum height

Conclusion

Understanding motion and time is fundamental to comprehending the physical world around us. This comprehensive guide for Class 7 CBSE Science covers all essential concepts, from basic definitions to complex equations of motion. By mastering these concepts, formulas, and problem-solving techniques, students will build a strong foundation for advanced physics topics in higher classes.

Regular practice with the provided questions, clear conceptual understanding, and application of formulas will ensure excellent performance in examinations. Remember that physics is not just about memorizing formulas but understanding the principles that govern the universe.

Note:

• Motion is relative and depends on the reference point
• Understanding the difference between scalar and vector quantities is crucial
• Distance and displacement are fundamentally different concepts
• Speed and velocity differ in their directional requirements
• The three equations of motion are powerful tools for solving motion problems
• Regular practice and conceptual clarity lead to mastery