Overview
This lecture covers the measurement of time and different types of motion, including ancient and modern timekeeping devices, concepts of periodic and oscillatory motion, speed, and reading distance-time graphs.
Measurement of Time
- Early humans measured time using periodic natural events like sunrise-to-sunrise and new moon-to-new moon.
- Ancient devices include the sundial (uses shadows), water clock (water flow), and sand clock (flowing sand).
- Modern devices for measuring time are wall clocks, table clocks, and digital clocks.
- A day is divided into 24 hours, 1 hour into 60 minutes, and 1 minute into 60 seconds.
- The SI basic unit of time is the second.
Periodic and Oscillatory Motion
- Periodic motion repeats itself after equal intervals of time; the pendulum is a classic example.
- Oscillatory motion means to-and-fro movement between two positions; each complete cycle is one oscillation.
- The mean position is the central, resting point; extreme positions are the farthest points reached.
- Time period: time taken to complete one oscillation.
Types of Motion
- Uniform motion: Equal distances covered in equal intervals of time; speed remains constant.
- Non-uniform motion: Distances covered are not equal in equal time intervals; speed varies.
- Circular motion: An object moves along a circular path.
- Oscillatory motion is a type of periodic motion.
Speed and Its Measurement
- Speed is the distance covered by an object per unit time (speed = distance/time).
- The SI unit of speed is meter per second (m/s), but kilometers per hour (km/h) is also common.
- Speedometer measures instantaneous speed; odometer measures total distance covered.
- Instantaneous speed is the speed at a specific moment.
- Average speed = total distance/total time, used when speed varies.
- To compare speeds, always convert units (e.g., km/h to m/s using: value × 5/18).
Distance-Time Graphs
- Distance-time graphs visually represent motion; uniform motion is shown by a straight line.
- Slope of the distance-time graph gives speed.
- In non-uniform motion, the graph is not a straight line, indicating changing speed.
- Data for graphs can be collected using odometer readings at regular time intervals.
Key Terms & Definitions
- Periodic Motion — Motion that repeats at regular time intervals.
- Oscillation — A single to-and-fro movement.
- Time Period — Time to complete one oscillation.
- Uniform Motion — Equal distances in equal time intervals.
- Non-uniform Motion — Unequal distances in equal time intervals.
- Speed — Distance covered per unit time.
- Instantaneous Speed — Speed at a specific moment.
- Average Speed — Total distance divided by total time.
- Speedometer — Device measuring current speed.
- Odometer — Device showing total distance traveled.
- Relative Motion — Motion of an object compared to another.
Action Items / Next Steps
- Complete the homework: Solve the question on drawing and interpreting a distance-time graph.
- Review types of motion and key definitions.
- Prepare any questions for the upcoming doubt-solving session.
- Join the class Telegram for notes and updates.