Section outline

    • Important Terms:

      1. Motion refers to the change in position of an object with respect to time.

      2. Speed is the distance covered by an object in a unit time.

      3. A non-uniform motion is when the speed of an object moving along a straight line keeps changing.

      4. A uniform motion is when an object is moving along a straight line is constant.

      5. Bob is the metallic ball of the pendulum.

      6.  Periodic or oscillatory motion is a to & fro movement.

      7. One oscillation of a pendulum is when the bob moves from one extreme position to other extreme position and back to the original position.

      8. Time period of a pendulum is the time taken by the pendulum to complete one oscillation,

      9. Distance time graph is a graphical representation showing the relationship between distance traveled & time taken by an object.

      10. One microsecond is one millionth of a second.

      11. A nanosecond is one billionth of a second. 

      12. Speedometer is the meter that measures speed of vehicles.

      13. Odometer is the meter that measures the distance covered by the vehicle.

      14. Formula for speed: Speed = Total distance / Total time taken

      15. A day is the time between one sunrise and the next one.

      16. A month is measured from one new moon to the next one.

      17. A year is the time taken by the earth to complete one revolution of the sun.

       

      Key Points:

      1, For uniform motion the average speed is the same as the actual speed.

      2. The basic unit for speed is meter per second (m/s), time is second (s), distance is meter (m).

      3. Speed of objects help us to decide which one is moving faster than the other.

      4. Other units of speed are: m/min (meter per minute) or km/h (kilometer per hour).

      5. Larger units of time are minutes (min) and hour (h).

      6. For longer distance the unit used is kilometer (km).

      7. The distance-time graph for the motion of an object moving with a constant speed is a straight line.

      8. Galileo Galilie discovered that the time period of a given pendulum is constant.

      9. Winding clocks and wristwatches were refinements of the pendulum clocks.

       

    • Motion

      Time

    • Quick revision notes:
      1. Types of motion:

      Straight Line motion:

      • Movement along a straight path.
      • Example: A car driving on a straight road, train moving on tracks, etc.

      Circular motion:

      • Movement along a circular path.
      • Example: A satellite orbiting Earth,  a car going around a circular track, a Ferris wheel, etc.

      Periodic or oscillatory motion:

      • Motion that repeats after a fixed interval or a to & fro motion.
      • Example: Motion of a pendulum swinging or a swing or seesaw, etc.
      2. Speed:
      • It tells how fast an object is moving.
      • Formula is: Speed = Distance / Time.
      • Distance is the total path covered by an object in motion.
      3. Time:
      • Different units of time like seconds, minutes, hours, day, week, month or year are used depending on the need. 
      • Ancient time measuring devices are sundial, water clocks, sand clocks, etc.
      • Nowdays, clocks that measure very small time intervals like microsecond, nanosecond are used for scientific research.
      • Time measuring devices used in sports can measure time intervals that are one tenth or one hundredth of a second.
      • Historical events are stated in terms of decades or centuries or millenniums.
      • The ages of stars and planet are often expressed in billions of years. 
      3. Pendulum:
      • The to and fro motion of a simple pendulum is an example of a periodic or an oscillatory motion.
      • Different positions of a simple pendulum is shown in the diagram below:

      • O is the mean position; A & B are the extreme positions of the bob of the pendulum.
      • It is one oscillation when the pendulum starts from position O to A, then A to O, O to B & From position B back to O.
      • Or one oscillation can be from one extreme position to another and back to the original position.
      • The time period of the pendulum only depends on the length of its string.
      • Galileo Galilie, a famous scientist discovered that for a given length of string of a pendulum the time period is constant.
      • Winding clocks and wristwatches are refinements of pendulum clocks.
      4. Distance- time graph:
      • It is a graphical representation showing the relationship between distance traveled and time taken.
      • X axis = Distance
      • Y axis = Time
      • Straight Line: indicates constant speed (steeper the line faster the speed).
      • Horizontal Line: indicates the object is at rest (no motion).
      • Curved Line: indicates changing speed (acceleration or deceleration).
      5. To remember:
      • To solve sums based on motion and time use correct formula.
      • Distance = Speed x Time & Time = Distance / Speed
      • Also check the units and convert into appropriate units when required.