Measurement of Physical Quantitites | Class 7 | Science | Chapter 6 | Maharashtra State Board
In this video, we'll explore the fascinating world of physical quantities and their measurement. We'll start by discussing what a physical quantity is and the difference between scalar and vector quantities. Then, we'll delve into the concepts of mass and weight, and how they are measured using standardized methods. We'll also introduce the International System of Units (SI) and the standard of the fundamental quantities. Finally, we'll discuss the importance of accurate measurement and the major causes of errors in measurement. Join us as we discover the science behind measuring the world around us!
Questions & Answers
1. Write answers to the following questions in your own words:
(a) Why is the weight of the same object different on different planets?
Ans. The weight of an object is determined by the gravitational force acting on it. The gravitational force depends on the mass of the planet and the distance from the object to the center of the planet. Since different planets have different masses and sizes, their gravitational forces vary. As a result, the weight of an object will be different on each planet.
(b) What precautions will you take to make accurate measurements in day-to-day affairs?
Ans. Following precautions will be taken to make accurate measurements in day-to-day affairs:
Use a balance stamped by the department of weights and measures.
Ensure the balance is stable and the pointer is upright.
Keep the pan free from tampering or additional weights.
Use metal weights for reliability and consistency.
(c) What is the difference between mass and weight?
| Mass | Weight |
1. | The amount of matter present in a substance is called mass. | The gravitational force that acts on this mass is called its weight. |
2. | Mass is a scalar quantity. | Weight is a vector quantity. |
3. | Mass remains same everywhere on the earth. | Weight changes from place to place on the earth. |
2. Who is my companion?
Group 'A' | Answer | Group 'B' |
Velocity | Metre/ second | Litre |
Area | Square metre | Kilogram |
Volume | Litre | Metre/ second |
Mass | Kilogram | Kilogram/ cubic metre |
Density | Kilogram/ cubic metre | Square metre |
3. Explain giving examples.
(a) Scalar quantity.
Ans. Scalar quantities, such as length, mass, temperature, and time, can be completely described by their magnitude alone. They are expressed using a numerical value and a unit of measurement. For example, a tunnel length of 2 km or a fever with a temperature of 101°F.
(b) Vector quantity.
Ans. A vector quantity is a physical quantity that has both magnitude and direction. For example, a displacement of a car 20 km towards the north or an airplane flying at a velocity of 500 km/hrs towards Mumbai.
4. Explain, giving examples, the errors that occur while making measurements.
Ans. The major causes of measurement errors are:
Using inappropriate devices.
Improper usage of devices.
For accurate measurements while shopping, remember to:
Use a balance with a standardization stamp.
Ensure balance stability and upright pointer.
Avoid tampering with the balance pan.
Use standardized metal weights.
5. Give reasons.
(a) It is not proper to measure quantities by using body parts as units.
Ans. The length of body parts varies from person to person, making it unreliable and inconsistent for obtaining accurate measurements.
(b) It is necessary to get the weights and measures standardized at regular intervals.
Ans. It is necessary to regularly standardize weights and measures to ensure accurate and reliable measurements. Over time, measuring devices can experience wear, calibration drift, or other factors that can introduce errors into measurements.
6. Explain the need for accurate measurement and the devices to be used for that.
Ans. Accurate measurement is essential for quality control, scientific research, engineering, healthcare, and environmental monitoring. It ensures reliability, safety, and informed decision-making. Common measurement devices include rulers, thermometers, scales, oscilloscopes, spectrophotometers, CMMs, and AFMs. The choice depends on the specific application and accuracy required.
E X T R A
1. Fill in the blanks.
The amount of matter present in a substance is called mass.
Mass is the qualitative measure of the inertia of an object.
The larger the mass, the greater is the inertia.
Mass is a scalar quantity.
Mass does not change from place to place anywhere in the world.
The gravitational force that acts on a mass is called its weight.
Weight is a vector quantity.
System International (SI) is also called metric system.
In Egypt in ancient times, the distance from a man’s elbow to the tip of his middle finger was called a cubit.
Gold was weighed in a unit called gunj.
2. Say whether true or false. Correct and rewrite the false statements.
(a) The standards of the six fundamental units are kept in the National Physical Laboratory at New Delhi.
Ans. True.
(b) Matter has a natural tendency to resist a change in its state, which is called inertia.
Ans. True.
(c) Weight and mass are both equal quantities.
Ans. False. Weight and mass are both different quantities.
(d) Work is a vector quantity.
Ans. False. Work is a scalar quantity.
(e) Velocity is a scalar quantity.
Ans. False. Velocity is a vector quantity.
(f) Unit of time in both the systems is second.
Ans. True.
(g) Unit of mass in C.G.S. system is kilogram.
Ans. False. Unit of mass in C.G.S. system is gram.
(h) Symbol of unit of second is sec.
Ans. False. Symbol of unit of second is ‘s’.
(i) 1 cubic foot means 28.317 ml.
Ans. False. 1 cubic foot means 28.317 litres.
(j) Vector quantity requires magnitude only.
Ans. False. Vector quantity required magnitude and direction both.
3. Give scientific reasons.
(a) Weight of our body on the moon is less than that on the earth.
Ans. The weight of an object is determined by the gravitational force acting on it. The moon has a smaller mass than Earth, which means it exerts a weaker gravitational force. As a result, when we stand on the moon's surface, we experience less gravitational pull compared to standing on Earth. This lower gravitational force leads to a decrease in our weight on the moon.
(b) Mass is a scalar quantity.
Ans. Mass is a fundamental property of matter and is scalar because it has only magnitude and no direction.
4. Distinguish between.
(a) Scalar quantity and Vector quantity.
| Scalar quantity | Vector quantity |
1. | A scalar quantity is a physical quantity that has only magnitude (size) and does not have a direction associated with it. | A vector quantity is a physical quantity that has both magnitude and direction. |
2. | Examples of scalar quantitites include mass, temperature, speed, energy, time and volume. | Examples of vector quantities include displacement, velocity, acceleration, force, momentum and electric field. |
(b) M.K.S. system and C.G.S. system.
| M.K.S. System | C.G.S. System |
1. | The MKS system uses the meter as the base unit for length, the kilogram as the base unit for mass, and the second as the base unit for time. | The CGS system uses the centimeter as the base unit for length, the gram as the base unit for mass, and the second as the base unit for time. |
2. | The MKS system is commonly used in fields like engineering, mechanics and everyday measurements. | The CGS system finds its application in scientific disciplines such as physics, chemistry and astronomy. |
5. Define.
(a) Mass.
Ans. The amount of matter present in a substance is called mass.
(b) Inertia.
Ans. Matter has a natural tendency to resist a change in its state, which is called Inertia.
(c) Weight.
Ans. The gravitational force that acts on the mass is called its weight.
(d) Physical Quantities.
Ans. The quantities in day to day life which can be measured are called physical quantities.
(e) Standardization.
Ans. The process of checking things against a standard measure from time to time is called standardization.
6. Answer the following.
(a) Why would the weight of an object be; maximum at the poles and minimum at the equator?
Ans. The weight of an object is maximum at the poles and minimum at the equator due to the Earth's shape and rotation. The Earth is slightly flattened at the poles and bulging at the equator. This shape, combined with the Earth's rotation, creates a gravitational field that is stronger at the poles and weaker at the equator, resulting in variations in weight.
(b) Why is the weight of an object at a high altitude less than its weight at the sea-level?
Ans. The weight of an object is less at a high altitude compared to sea level due to the decrease in gravitational pull. As you move higher above the Earth's surface, the distance between the object and the center of the Earth increases. Since the force of gravity weakens with distance, the gravitational pull on the object decreases, resulting in a lower weight.
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