Measurement of Length and Motion

  

Measurement of Length and Motion:

Various means of measurement, such as the palms, fingers, arm length and feet, were used to measure length and distance before standardized systems were introduced.

Non-standard measures: The lengths of steps, arms, hands, or fingers of different people are different, therefore the distance measured with their help is not always reliable. These methods are, therefore, called non-standard measures.

1 cubit = The length of the arm from the elbow's point to the end of the middle finger.

1 handspan = The distance between the thumb and the little finger when it is stretched is known as hand-span.

1 footspan - The measurement of an object using your foot is called footspan.

 1 armlength - The measurement of an object using your arm is called armlength.

Disadvantages of Non-standard Units of Measurement: You have seen that arbitrary units are made up of lengths of different body parts. These lengths can vary from one person to another. This can create lot of confusion as there would be no uniformity in measurement.

Standard Measures:

In October 1960, the 12th General Conference on Weight and Measures adopted the International System of Units are called as SI Units, (named after the French word, Systems International d’Unites)  is the set of units to maintain uniformity all over the world.

SI Unit (International System of Units): It is the most widely used system of measurement in the world. It is based on MKS (Meter-Kilogram-Second) System. Length, weight and time are considered as basic quantities for measurement and other quantities are derived from them. As per SI system; the unit of length is meter, unit of weight is kilogram and the unit of time is second.

Motion:

The act, process or state of the change in place or position of a body with respect to time and relative to the observer is said to be motion. For example the blades of a rotating fan, the hands of a working wall clock, a moving car, a spinning top and satellites are all in motion.

Rest:

 When a body remains in one position for a long time, it is said to be at rest. For example, the chairs of the dining table are at rest unless and until they are moved, and the flower vase, table, and the blackboard in the class room are all at the position of rest.

Types of Motion

The various types of motion are:

       Ø  Translatory motion – linear motion, curvilinear motion, circular motion, Random motion

Ø  Rotatory motion ( or Rotational motion)

Ø  Rolling motion

Ø  Periodic motion

Ø  Oscillatory and vibratory motions

   

 

Linear Motion: When the motion is in a straight line, it is called linear motion, e.g. a car moving on a straight road.

Curvilinear Motion: When the motion is on a curved path, it is called curvilinear motion, e.g. a car moving on a bend.

Random motion: When object moves from one position to another and changes direction in an irregular manner.

Example: butterfly flies randomly in garden.

Circular Motion: When the motion is on a circular path, it is called circular motion, e.g. the motion of the earth in its orbit, the blades of a fan.

Rotation: When an object moved around an axis, it is called rotation, e.g. rotation of the earth on its axis.

Rolling motion: Any motion containing both the rotational as well as translatory motion is rolling motion, e.g. motion of a bicycle wheel, the movement of a drill.

Periodic Motion: When the motion is repetitive after a fixed interval, it is called periodic motion, e.g. motion of a wing, motion of earth around the sun.

Oscillatory motion: The to-and–fro motion of a body along the same path is called oscillatory motion, e.g. a child on a swing.

Vibratory motion: Small and rapid to-and-fro movement of a body or a part of it from its mean position is called vibratory motion, e.g. vibrations in the string of a guitar.

 

EXERCISES ( QUESTION - ANSWERS)

A. Choose the correct answer.

1. (d)     2. (d)     3. (d)     4. (a)     5. (a)     6. (b)     7. (a)     8. (c)

B. Fill in the blanks.

1. measuring tape     2. metre     3. thread     4. vibratory     5. rolling

C. State True or False. Also correct the false statements.

1. True             

2. False, the SI unit of distance is metre.         

3. True

4. False, motion of a fly is an example of random motion.         

5. True

II. LOGIC BASED QUESTIONS

Short and Long Answer

1. (a) an ant—Random

    (b) a car moving on the straight road—Translatory

    (c) pendulum of a clock—Periodic/vibratory

    (d) potter’s wheel—Rotational

    (e) whirling a stone tied to a string—Circular

    (f) a spin ball—Rolling (translatory as well as rotatory)

2. A handspan cannot be used universally as a unit of length because the length of a hand varies from        person to person.

3. Yes, motion on this non-circular track can be periodic. Periodic motion refers to any motion that             repeats itself at regular intervals of time. If an object moves on this non-circular track and returns to      its starting point after completing one lap in the same period of time for each lap, the motion will be     periodic. The shape of the track (whether circular or non-circular) does not affect periodicity as long     as the motion satisfies the condition of repetition at regular time intervals.

6. 1 km > 1 m > 1 cm  > 1 mm

7. (a) Rotational motion of the wheels about their axes.

    (b) Translatory motion of the wheels along the road.

    (c) Rolling motion.

III. HIGHER ORDER THINKING SKILLS

1. The trees outside a train appear to move while co-passengers appear stationary because the position of the trees changes relative to the passengers, but the position of the co-passengers does not change.

2. When a screw is turned, it undergoes two types of motion at the same time :

        • Rotatory motion : The screw rotates around its own axis.

        • Translatory motion : The screw moves forward in a straight line.

3. If the zero mark on a scale is not visible, one can measure the length of an object by placing it on a visible mark on the scale and subtracting the reading on that mark from the reading at the other end.