Chapter 9 – Speed and Time

Chapter 9 – Speed and Time

 

1. Motion

• When an object changes its  position  with time, it  is said to be  in motion.
• If an object does not change its position, it  is said to be  at rest.
• Types of Motion :
  •  Rectilinear Motion: Motion in a straight line. Example: The speed of the car on a straight road.
  •  Circular Motion: Motion on the path of a circle. Example: Motion of the moon around the Earth.
  •  Periodic motion: The speed that repeats itself at fixed time intervals. Examples: the motion of a pendulum, the speed of a swing.

 

2. Slow and Fast Motion

• The motion of an object can be classified by looking at how far it travels or how quickly it travels the distance.
•  Fast Motion: Covering more distance in less time.
•  Slow Motion: Covering a short distance in a long time.

 

3. Speed

• Speed is the distance that an object  travels per unit time.
• Formula :

Walk = Time taken Distance covered

• Unit: The basic unit of speed  is meters per second (m/s).  Other units are also kilometers per hour (km/h) or centimeters per second (cm/s).
•  Average Speed: When an object moves at an unequal speed,  the average speed is calculated by dividing its total distance traveled by the total time taken.

 

4. Measurement of Time

• Time is the period during which events occur.
• In ancient times people used natural phenomena to measure time:
  • The Rise and Setting of the Sun: One Day.
  • From one new moon to the next: one month.
  • Earth’s rotation around the Sun: one year.
•  Clocks and Timepieces:
  • Today we use clocks, timepieces, stopwatches, etc. to measure time.
  • All of them work on the principle of periodic motion.
•  Simple Pendulum:
  • A small metal sphere  (bob) in a simple pendulum is suspended by a thread.
  • It moves back and forth in a certain time interval (periodic motion).
  •  Time Period of Oscillation: A complete oscillation (the time taken to travel from one end to the other and back to the same end) is called the oscillation period.
  • It was used as the basis for watches and timepieces.

5. Measuring Speed

•  Speedometer: An instrument in a vehicle that directly shows the vehicle’s speed in kilometers per hour (km/h).
•  Odometer: Another device in vehicles that records the distance traveled by the vehicle.

 

6. Distance-Time Graphs

Distance-time graphs are used to depict the motion of an object graphically.

1. Uniform Motion:

• • If an object covers the same distance in a certain interval of time, its speed is uniform.
  • A distance-time graph is a  straight line.

 

1. Non-Uniform Motion:

• If an object covers an unequal distance in a certain interval of time, its speed is non-uniform.
• A distance-time graph is a  curved line.