Science: Class 7 — Chapter 9: Motion and Time

9.1 Slow or Fast

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

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

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

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

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.