By Subhash Kumar | Science Educator | UREducator
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Motion and Time
Complete Teaching Resource for CBSE Class 7 Science Chapter 9
Class: VII
Subject: Science
Chapter: 9
Duration: 4 Hours
What Students Will Achieve
Knowledge
- Define motion and identify different types of motion
- Explain the concept of speed and how to calculate it
- Differentiate between uniform and non-uniform motion
- Understand the working of simple pendulum and its time period
Understanding
- Explain why our perception of speed can be misleading
- Analyze how distance-time graphs represent motion
- Understand the relationship between speed, distance and time
- Explain how periodic motion is used to measure time
Skills
- Calculate speed from distance and time measurements
- Construct and interpret distance-time graphs
- Measure time period of a simple pendulum
- Compare speeds of different moving objects
Prior Knowledge Assessment
Starter Questions:
- What are the three main types of motion you learned in Class VI?
- How would you determine which of two vehicles is moving faster?
- What device in vehicles shows the distance traveled?
Different Categories of Movement
Classification of Motion
Rectilinear Motion
(Straight line motion)
- Movement along a straight path
- Example: Car moving on straight road
- Can be uniform or non-uniform
- Simplest type of motion to analyze
Circular Motion
(Movement along circular path)
- Object moves along circumference of circle
- Example: Merry-go-round, clock hands
- Direction continuously changes
- Centripetal force required
Periodic Motion
(Repeats at regular intervals)
- Motion that repeats in equal time periods
- Example: Pendulum, swing, bouncing ball
- Used in time measurement devices
- Also called oscillatory motion
Examples of Different Motions
| Example | Type of Motion | Explanation |
|---|---|---|
| Soldiers marching | Rectilinear | Moving in straight line formation |
| Clock hands | Circular | Moving around central point |
| Swing | Periodic | Back-and-forth motion repeats |
| Earth around Sun | Circular | Nearly circular orbital path |
Activity: Identifying Motion Types
Objective: Observe and classify different types of motion
- List 10 moving objects in your environment
- Observe each object's movement carefully
- Classify each as rectilinear, circular or periodic
- Note any objects that show combination of types
- Discuss your classifications with classmates
Understanding and Calculating Speed
Key Concepts of Speed
Definition
- Distance covered per unit time
- Measure of how fast something moves
- Scalar quantity (magnitude only)
- Different from velocity (which includes direction)
Calculation
- Speed = Distance ÷ Time
- Basic unit: meters per second (m/s)
- Common unit: kilometers per hour (km/h)
- 1 m/s = 3.6 km/h
Uniform vs Non-uniform
- Uniform: Constant speed (straight distance-time graph)
- Non-uniform: Changing speed (curved distance-time graph)
- Average speed = Total distance ÷ Total time
- Instantaneous speed at a moment
Speed Comparison Table
| Object | Speed (km/h) | Speed (m/s) |
|---|---|---|
| Falcon (fastest bird) | 320 | 88.9 |
| Cheetah | 112 | 31.1 |
| Human runner | 40 | 11.1 |
| Snail | 0.05 | 0.014 |
Experiment: Calculating Speed of Objects
Objective: Measure and compare speeds of different objects
- Mark a 10-meter straight track on ground
- Time how long different objects take to cover distance
- Test: walking, running, rolling ball, toy car etc.
- Calculate speed for each (Speed = Distance/Time)
- Compare results and rank objects by speed
Measuring Time Intervals
Methods of Time Measurement
Simple Pendulum
- Consists of bob suspended by string
- Exhibits periodic to-and-fro motion
- Time period depends on length
- Used in early clocks
Historical Methods
- Sundials: Use sun's shadow
- Water clocks: Measure water flow
- Sand clocks: Measure sand flow
- Based on natural periodic events
Modern Clocks
- Quartz clocks: Use crystal vibrations
- Atomic clocks: Most accurate
- Digital clocks: Electronic displays
- All use periodic processes
Time Units and Conversion
| Unit | Equivalent | Usage |
|---|---|---|
| Second (s) | Base unit | Scientific measurements |
| Minute (min) | 60 seconds | Everyday time measurement |
| Hour (h) | 60 minutes | Longer durations |
| Day | 24 hours | Earth's rotation period |
Experiment: Measuring Pendulum Time Period
Objective: Determine time period of a simple pendulum
- Set up pendulum with 1m string and small bob
- Displace bob slightly and release (don't push)
- Measure time for 20 complete oscillations
- Calculate time period (Time/20)
- Repeat with different string lengths
Visualizing Motion with Graphs
Graph Interpretation
Graph Components
- X-axis: Usually time
- Y-axis: Usually distance
- Slope: Represents speed
- Steeper slope: Higher speed
Uniform Motion
- Straight line graph
- Constant slope
- Speed remains unchanged
- Easy to calculate speed from slope
Non-uniform Motion
- Curved or changing slope
- Speed varies over time
- Average speed can be calculated
- Instantaneous speed at points
Creating a Distance-Time Graph
Let's plot the motion of a car that covers these distances at regular intervals:
| Time (min) | Distance (km) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 2 |
| 3 | 3 |
| 4 | 4 |
| 5 | 5 |
Time (minutes)
Distance (kilometers)
This straight line graph indicates uniform motion with constant speed of 1 km/min.
Activity: Creating Motion Graphs
Objective: Plot and interpret distance-time graphs
- Collect distance-time data from experiment
- Choose appropriate scales for axes
- Plot points accurately on graph paper
- Connect points to form graph
- Analyze graph to determine speed
- Compare graphs of different motions
Evaluation Strategies
Formative Assessments
- Motion classification exercises
- Speed calculation problems
- Pendulum experiment reports
- Graph interpretation questions
Summative Assessments
- Chapter test (MCQs + problems)
- Practical test on pendulum timing
- Graph construction and analysis
- Real-world application scenarios
Extended Learning: Transportation Analysis
Objective: Apply motion concepts to real transportation
- Research different transportation speeds (walking, cycling, cars, trains)
- Calculate travel times for different distances
- Create distance-time graphs for comparison
- Analyze how speed affects travel planning
- Present findings with visual aids
Frequently Asked Questions
Why does the time period of a pendulum remain constant?
The time period of a simple pendulum depends primarily on:
- Length of string: Longer strings have longer periods
- Gravitational acceleration: Varies slightly by location
- It is independent of:
- Mass of the bob
- Initial displacement (for small angles)
- Amplitude of swing
- This constancy makes pendulums useful for timekeeping
How can we determine speed from a distance-time graph?
Speed can be determined from the graph's slope:
- Straight line graph: Constant speed (slope = speed)
- Curved graph: Changing speed (slope at point = instantaneous speed)
- Calculation:
- Select two points on the line
- Calculate change in distance (Δy)
- Calculate change in time (Δx)
- Speed = Δy/Δx
- Steeper slope = higher speed
