Living Science 2020 2021 for Class 6 Science Chapter 11 - Measurement And Motion

Answer:

Speed of a car and the distance from earth to sun are the only physical quantities, as they both can be measured and expressed in terms of fundamental quantities. But, how angry a person is or how much a mother loves her child are the emotions and can not be measured or expressed in terms of fundamental quantities. So, they are not physical quantities. 

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A standard unit is a fundamental measure of a physical quantity. It does not matter where we are, the physical quantities will always be expressed in a similar way. The standard unit for length is 'meter', for mass, it is 'kilogram' and for the time it is 'second'. These units are fundamentals, which will remain the same on the moon as well. For example, Gravity on the moon is different than the gravity on the earth, but the standard unit to measure the gravity on earth and the moon are the same, i.e. m/s².

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SI units are the fundamental units for various physical quantities accepted all over the world. The Si unit given for length is 'meter', for mass it is 'kilogram' and for the time it is 'second'. Though length, mass and time can be expressed in terms of other units as well but these are the standard units used uniformly all over the world. 

Answer:

Units are always expressed as singular words and their short abbreviation is taken as the full expression. The correct way of writing the given quantities is as follows:

(a) 10 kg
(b) 5 cm
(c) 1 kg
(d) 20 cm

Answer:

Yes, I agree. Whether an object is at rest or in motion depends on the frame of reference or the point of observation. For example, if a man A and man B are sitting inside the bus and a third man C is standing outside. Now, if the bus starts moving then man A will see man B at rest no matter how fast the bus is moving. But, man C will see man B moving along with the bus, for him man B is moving with the speed of the bus. So, we can say that man B is rest with respect to man A but he is moving with respect to man C. The difference in observations comes due to different points of observation or different frame of reference.
 

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Both the motions are translational in nature. A motion is said to be translational when the body undergoing motion changes its position with respect to time. As in rectilinear motion and curvilinear motion both, the objects are changing their positions, so both are pursuing translational motion. 

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In translational motion, an object changes its position such that every point in the body experiences the same velocity at any instant of time. Here, due to the spinning of the top about its axis, the velocity of different points of the top becomes different, so it's motion cannot be considered a translatory motion. When an object changes its orientation about a fixed axis, then the motion of the object is said to be rotational motion. Therefore, the spinning top is undergoing rotational motion.

Answer:

Yes, earth has both translatory as well as rotational motion. When the earth revolves around the sun it changes its position, that motion is translational in nature. But when the earth spins around its own axis, the motion is rotational motion. The earth revolves around the sun while spinning about its own axis, that's why the earth is known to have translatory and rotational motion both. 

The motion of a wheel of a cycle is also an example when the body is in translatory and rotational motion both. The wheel of the cycle rotates about its own axis while it moves forward. 
 

Answer:

(b) it varies from person to person.

The footstep as a measure of length is unreliable measure of length because different people have different foot sizes.

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(c) metre

The standard unit of length in the SI system is metre (m).

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(c) 1000

1 metric ton is equal to 1000 kilograms.

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(b)  should be vertically above the point where the measurement is to be taken.

The eye must be vertically above the point where the measurement is to be taken to avoid parallax error.

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(c) all of us in our daily life.

The estimation is important for all of us everywhere, in daily life as well as in laboratory.

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(b) Curvilinear motion.

Object moving along curved path is a curvilinear motion. Curvilinear motion is a type of translatory motion.

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(c) Periodic motion.

The repetitive to and fro motion of a pendulum is an example of periodic motion.

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(b) rotation of the earth.

The rotation of earth about its own axis is a rotational motion.

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(d) Rectilinear motion.

In rectilinear motion, the direction of movement of the body does not change.

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(a) beating of a drum.

Beating of a drum is a non-periodic motion, as interval of time after which the beating is repeated is not constant.

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A quantity that can be measured is called a physical quantity.

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True, if you are using the SI system, you will always measure length in metres.

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False. In daily life, it is often sufficient to arrive at a good estimate.

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In the year 1960, India started using metric measurements.

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True, the standard units of mass, length and time are the same in the MKS and the SI systems.

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The statement, "While measuring length using a metre scale, the position of the eye does not affect the measurement", is false. When using metre scale, one needs to keep the eye vertically above the measurement point.

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In translatory motion, all the the parts of the body move through same distance in the same time interval.

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The earth performs rotational motion around its own axis.

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In periodic motion, an object moves to and fro about its position of rest.

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Fast, periodic motion, such as hitting a tabla, produces sound.

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The motion of earth around its own axis is rotational motion. Also, earth revolves around the sun along a circular path. This is translatory motion.

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Earlier, different countries had different measurements units, which caused confusion. Later, in the year 1960, the general conference of weights and measures suggested the usage of common system world over. This system is called as the systeme international d'unites (SI) system.    

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(a) In CGS system, the units of mass, length and time are gram, centimetre and second respectively.
(b) In SI system, the units of mass, length and time are kilogram, metre and second respectively.

Answer:

To make accurate measurements there are following two main requirements:
(i) One must have an appropriate instrument.
(ii) He should know how to use the instrument properly.

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An object is in motion when it changes its position with time, relative to a stationary object.

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First the invention of a wheel brought a revolution in transport. The second revolution in the field of transport occurred with the invention of steam engine. 

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The first motion is rotational motion, wherein the earth rotates around its own axis.
Second motion is translatory motion, where the earth moves around the sun in a circular path.

Answer:

When making measurements which involves very large numbers or very small numbers, using one standard unit of length becomes very difficult and impractical. Therefore, for measurements involving small numbers submultiples of standard units are used and for large numbers multiples of standard units are used.

Answer:

While measuring the length of a line segment following precaution should be taken:
(a) The ruler should be placed exactly on the length to be measured.
(b) One should not use worn out portions of the instrument. 
(c) Eyes should be kept vertically above the point to be measured.

Answer:

To measure the length of a curved line, we can use a piece of string. Knot the string at the beginning as shown in the figure below and press it against the beginning of the line with your forefinger.




The second method is to use a set of dividers. This is shown in the figure below.

Answer:

(a) Accurate measurements are of importance in situations where extreme precision is essential, such as in scientific experiments or in construction of fine tolerance machinery. Here
even an error in measurement of weight by 0.1 g can completely change the result of an experiment.
(b) Estimation will suffice in most daily, domestic situations such as the mixing sugar or salt in food items. Here, a difference of 0.1 g in the amount of salt or sugar in food will not even be noticed.

Answer:

The two different types of translatory motion are:

1. Rectilinear/Linear motion: In this case, the object moves along a straight line path. For example, a car driving along a straight road is performing rectilinear motion.
2. Curvilinear motion: When an object moves along a curved path, then the motion is said to be curvilinear motion. A car moving on a curved road is an example of curvilinear motion.

Answer:

When motion of an object keeps repeating itself at a regular interval of time, it is said to be a periodic motion.
Examples:
(a) A pendulum, i.e. a ball tied to a string, undergoes a periodic motion.
(b) A swing also performs a periodic motion in a similar manner.

Answer:

No, in our daily life it is not so important to measure everything accurately. For example, adding sugar to a tea can have slight variation, it need not be very accurate.

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When a screw is turned, first it performs rotational motion along its own axis. Secondly, while rotating it also performs translatory motion.

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The motion of an oscillation pedestal fan is rotational motion. Also, the fan also performs oscillatory motion.

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A spinning top performs a rotational motion, revolving about its own axis and at the same time if it moves around, it performs translatory motion.

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The tree fixed on earth and earth is moving. So, with respect to distant fixed stars, the tree can be considered to be in motion.