Class 6 Measurement-distance-motion

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1. What is motion?
2. The distance between two bus stops is 35 m. Express this distance in (a) cm (b) km
3. What is the SI unit of the following?
(a) length (b) mass (c) time (d) temperature
4. Why can footstep or a hand span not be used as a standard unit of length?
5. When is a body said to be at rest?
6. Name the two instruments which are used to measure very small lengths.
7. Name two things which can be used to measure the length of a curved line.
8. Define uniform motion and give one example.

Ans:

1. The objects which change their positions with time (with respect to their surrounding)
are said to be in motion.
2. Distance = 35 m
We know, 1 km = 1000 m
So, distance = 35/1000 = .035 km
we know that:
1 m = 100 cm
So, 35 m = 35 × 100 cm= 3500 cm
3. (a) length — metre
(b) mass — kilogramme
(c) time — second
(d) temperature — Kelvin
4. Footstep or a hand span cannot be used as a standard unit of length as such units of measurements are not reliable, they vary from person to person, place to place and are affected by the local conditions.
5. The objects which cannot change their position (with respect to their surrounding) are said to be at rest.
6. Measuring tape and metre scale.
8. When a body travels an equal distance in equal intervals of time, it is said to be in uniform motion. For example, Planets move around the sun in uniform motion.

Ans:

1. Motion in a straight line is called rectilinear motion. In other words, when an object moves along a straight line path it is called rectilinear motion. So, the movement of a bullet fired from a gun is an example of rectilinear motion.
2. The translatory motion of a body which keeps on changing its direction in a disorderly manner is called random
motion. The motion of a cricket ball during a cricket game and that of a football match and motion of a flying bird in the sky are examples of random motion.
3. The motion which repeats itself after regular intervals of time is called periodic motion. For example, the motion of a swing or a pendulum is periodic.
4. Circular and rotatory motion
5. When a body moves to and fro about a point, it is said to be in oscillatory motion.
The oscillatory motion is a kind of periodic motion. Some examples of oscillatory motion are:
• The motion of the heart muscles in a healthy person.
• A child on a swing.
6. The motion which repeats itself after regular intervals of time is called periodic motion. A motion which repeats itself but not in a fixed interval of time is called a non-periodic motion.
7. In taking a measurement of length, we need to take the following precautions (care) to get the correct measurement of the length.
(a) Placement of scale: The scale should be placed with the objects along its length.
(b) Worn out ends of the ruler: Sometimes, due to repeated use the zero mark of a scale gets worn out and cannot be clearly seen. In some cases, the ends of the scale may get damaged or broken due to various reasons. In such cases, we should measure the length of the object starting from any other mark of the scale (say the 1 cm mark).
We subtract the reading of this mark (1cm) from the reading of the other end.
(c) The position of the eye: The correct position of the eye is also important for taking a measurement.
8. Classify the following motions:
(i) the motion of wheels of a car—circular motion
(ii) motion of a string of a guitar when played by a musician—vibratory motion
(iii) rotation of the earth on its own axis— circular motion.

Measurement of distance and motion

1. What is meant by rectilinear motion? Give two examples of rectilinear motion.
2. Define random motion. Give one example.
3. What is meant by periodic motion?
4. What two types of motion does the earth show?
5. What is an oscillatory motion? Give two examples.
6. How is a periodic motion different from non-periodic motion?
7. List the precautions to be observed while measuring the length using a scale.
8. Classify the following motions:
(i) the motion of wheels of a car
(ii) motion of a string of a guitar when played by a musician
(iii) rotation of the earth on its own axis.

Ans:

1. Motion in a straight line is called rectilinear motion. In other words, when an object moves along a straight line path it is called rectilinear motion. So, the movement of a bullet fired from a gun is an example of rectilinear motion.
2. The translatory motion of a body which keeps on changing its direction in a disorderly manner is called random
motion. The motion of a cricket ball during a cricket game and that of a football match and motion of a flying bird in the sky are examples of random motion.
3. The motion which repeats itself after regular intervals of time is called periodic motion. For example, the motion of a swing or a pendulum is periodic.
4. Circular and rotatory motion
5. When a body moves to and fro about a point, it is said to be in oscillatory motion. The oscillatory motion is a kind of periodic motion. Some examples of oscillatory motion are:
• The motion of the heart muscles in a healthy person.
• A child on a swing.
6. The motion which repeats itself after regular intervals of time is called periodic motion. A motion which repeats itself but not in a fixed interval of time is called a non-periodic motion.
7. In taking a measurement of length, we need to take the following precautions (care) to get the correct measurement of the length.
(a) Placement of scale: The scale should be placed with the objects along its length.
(b) Worn out ends of the ruler: Sometimes, due to repeated use the zero mark of a scale gets worn out and cannot be clearly seen. In some cases, the ends of the scale may get damaged or broken due to various reasons. In such cases, we should measure the length of the object starting from any other mark of the scale (say the 1 cm mark).
We subtract the reading of this mark (1cm) from the reading of the other end.
(c) The position of the eye: The correct position of the eye is also important for taking a measurement.
8. Classify the following motions:
(i) The motion of wheels of a car—circular motion
(ii) motion of a string of a guitar when played by a musician—vibratory motion
(iii) rotation of the earth on its own axis— circular motion.

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