Chapter 9: Motion and Time
9.1 Slow or Fast
Types of Motion
- Straight line motion: Motion along a straight path (e.g., soldiers in a march past).
- Circular motion: Motion along a circular path (e.g., Earth orbiting the Sun).
- Periodic motion: Motion that repeats itself after regular intervals (e.g., motion of a swing or pendulum).
9.2 Speed
Understanding Speed
- Speed: The distance covered by an object in a unit time.
- Formula: Speed = Total distance covered / Total time taken.
- Non-uniform motion: When the speed of an object moving along a straight line keeps changing.
- Uniform motion: When an object moves along a straight line with a constant speed.
9.3 Measurement of Time
Clocks and Pendulums
- Periodic events: Natural events repeating at regular intervals (e.g., sunrise to sunrise is a day).
- Simple pendulum: Consists of a small metallic ball called a bob suspended from a rigid stand by a thread.
- Oscillation: The to-and-fro motion of a pendulum from one extreme position to another and back.
- Time period: The time taken by the pendulum to complete one full oscillation.
- Units: Basic unit of time is second (s). Basic unit of speed is m/s (meters per second).
9.4 Measuring Speed
Calculations and Devices
- Distance formula: Distance = Speed × Time.
- Time formula: Time = Distance / Speed.
- Speedometer: An instrument on vehicles that records speed directly in km/h.
- Odometer: An instrument that measures the total distance travelled by a vehicle.
9.5 Distance-Time Graph
Graphical Representation
- Bar graph: Represents data using rectangular bars.
- Pie chart: Represents data in a circular, proportional format.
- Line graph: Represents continuous data over time; a distance-time graph is a line graph.
- Constant speed: Represented by a straight line on a distance-time graph.