Measurement of Distance and Motion

     

Measuring Length and Distance:

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.

 

Chapter 10

Measurement of Distance and Motion (Answers)

Measurement of Distance and Motion

 

A.            Very Short Answer Questions:

 

1.  Metre

 

2.  Metre scale and measuring tape

 

3.  Motion

 

4.  Vibration

 

5.  Rest

 

B.            Short answer type questions:

 

1.  What does each measurement consist of ?

Ans: Numerical value of measure and the unit in which that quantity is measured.

 

2. On what factors does the choice of measuring device depend ?

Ans: It depends on –

a.  The quantity to be measured.

b.  The range of measurement.

c.   The precision to which a quantity is to be measured.

 

3.  What is meant by the rotatory motion ?

Ans: When the motion of an object is around a fixed point that is inside the object, it is called rotatory motion.

 

4. Name the three types of translatory motion. Give one example of each type.

Ans: Three types of translatory motion are:

a.  Linear motion (or Rectilinear motion)

Example: the motion of a car along a straight road.

b.  Curvilinear motion (or circular motion)

Example: the motion of a car when it turns, it moves along a curved path.

c.   Random motion

Example: the motion of a football or hockey player on the ground.

 

5. Define random motion. Give one example.

Ans: The translatory motion of a body which keeps on changing its direction in a disorderly manner is called random motion.

Example: motion of an ant.

 

C.             Long Answer type Questions:

 

1. Why we need standard units of measurements?

 

Ans: We need a standard unit for measurement to make our measurement more common, reliable and accurate. While taking a measurement, the value should be same for everyone. In order to do that, we have a common unit of measurement called a standard unit. SI units are used everywhere in the world for the sake of uniformity.

 

2. Mention the precautions to be observed while measuring the length of a pencil using a ruler.

 

Ans: The precautions which should be taken while using a ruler to measure length of a pencil are the following:

 

                    i.        The scale should be placed along the length to be measured. The scale should be placed very close to the object to be measured.

                 ii.        Keep your eye in line with the point of measurement.

               iii.        Do not start measurement from the worn out or damaged end of the scale.

 

3. While measuring the length of a metallic rod the reading of the scale at one end is 8.0 cm and at the other end is 33.7 cm. What is the length of rod ?

Ans: Reading of measurement at second end= 33.7 cm

Reading of measurement at first end= 8 cm

length of rod = reading of second end -  reading of first end

length of rod = 33.7 cm – 8 cm

length of rod = 25.7 cm                                      

 

4. Name the types of motion executed by a rolling body. Give one example of rolling motion.

 

Ans: The types of the motion executed by a rolling body are as:

a) Translatory motion

b) Rotatory motion

Example: The motion of a bicycle wheel

 

5. Define circular motion. Give one example also.

 

Ans: When the motion of an object is around a fixed point that is outside the object, it is called circular motion.

Example: The motion of a stone tied to a string and whirled in a circle.

 

E. Define the following terms

1. The position of rest

2. Curvilinear motion

3. Standard unit of measurement

4. Periodic motion

5. Vibratory motion

 

Answers:

 

1.         The position of rest: A body is said to be at rest if it does not changes its position continuously with respect to its surroundings with the passage of time.

Example: A book lying on a table.

 

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

 

3.         Standard units of measurement: For bringing the uniformity in units, scientists have done lot of efforts on International level and prepared an unanimous standard system. It is known as International Standard System. It is abbreviated as SI units.

In this system length is measured in metre; mass in kilogram and time in second.

 

4.         Periodic motion: Periodic motion is the motion which repeats itself after regular intervals of time.

 

5.         Vibratory motion: Small and rapid oscillations are called vibrations. Small and rapid to-and-fro movement of a body or a part of it from its mean position is called vibratory motion. Vibratory motion produces sound.