Q1. Write answers to the following questions in your own words.

(i) Why is the weight of the same object different on different planets?

Answer. The weight of an object depends on the gravitational force of the planet it is on. Different planets have different gravitational pulls due to their size, mass, and density. For example, Earth’s gravity is stronger than the Moon’s, so an object will weigh less on the Moon than on Earth. This is why the same object can have different weights depending on which planet it is placed.

(ii) What precautions will you take to make accurate measurements in day-to-day affairs?

Answer. To make accurate measurements in everyday situations, I will ensure that the measuring instrument is calibrated correctly. I will place the instrument on a flat and stable surface to avoid tilting. Additionally, I will read measurements at eye level to reduce errors caused by viewing angles and use appropriate units of measurement for each task. Regularly checking the accuracy of tools and using standard measuring devices also helps improve precision.

(iii) What is the difference between mass and weight?

Answer. Mass is the amount of matter in an object, and it remains constant no matter where the object is located. Mass is measured in kilograms (kg). Weight, on the other hand, is the force with which gravity pulls on an object. It can change depending on the strength of gravity where the object is. Weight is measured in newtons (N). For example, an object with a mass of 10 kg will weigh less on the Moon than on Earth due to the lower gravity on the Moon.

Q2. Who is my companion?

Group A	GroupB
(1)Velocity	(a)litre
(2)Area	(b)Kilogram
(3)Volume	(c) meter/second
(4)Mass	(d)Kilogram/cubic metre
(5)Density	(e) Square metre

Group A	GroupB
(1) Velocity	(c) meter/second
(2) Area	(e) square metre
(3) Volume	(c) litre
(4) Mass	(d)Kilogram
(5) Density	(e) Kilogram/Cubic metre

Q3. Explain by giving examples.

• Scalar quantity:

Answer. A scalar quantity is a measurement that only has size or magnitude but no direction. It can be positive or negative, depending on the situation. For example, temperature is a scalar quantity because it only measures how hot or cold something is, without needing to indicate any direction. Speed is another example; it tells you how fast something moves but not in which direction.

• Vector quantity:

Answer. A vector quantity has both magnitude and direction. For example, velocity tells you not only how fast something is moving but also in which direction, like 60 km/h north. Another example is force, such as pushing an object with 10 newtons of force towards the east.

Q4. Explain giving examples of the errors that occur while making measurements.

Errors in measurements can happen due to various reasons:

• Human Error: These occur when a person reads the measuring scale incorrectly or doesn’t use the instrument properly. For example, reading the scale from an angle instead of directly in front can lead to inaccurate readings.
• Instrumental Error: This happens when the measuring device itself has flaws. For example, if a weighing scale is not properly calibrated, it might give incorrect weight measurements.
• Environmental Error: These occur due to changes in the environment like temperature, pressure, or humidity. For example, a metal ruler may expand slightly in hot weather, which can affect the accuracy of length measurements.

Q5. Give reasons.

• It is not proper to measure quantities by using body parts as units.

Answer. Using body parts like a hand span or foot to measure things is not accurate because everyone’s body parts are of different sizes. This means that measurements can vary from person to person, leading to inconsistent results. For example, my foot size may be different from someone else’s, so measuring distance using our feet would not be reliable.

• It is necessary to get the weights and measures standardized at regular intervals.

Answer. Standardizing weights and measures ensures that everyone uses the same measurements, which makes trade, construction, and everyday activities more accurate and fair. Regular checks help to ensure that measuring devices like scales and rulers are not worn out or inaccurate. This consistency is crucial for businesses and industries, where precision can affect quality and fairness.

Q6. Explain the need for accurate measurement and the devices to be used for that.

Answer. Accurate measurements are essential in everyday life because they ensure that tasks are done correctly and safely. For instance, when cooking, precise measurements of ingredients ensure the right taste and texture. In construction, accurate measurements help to build safe structures. For medical purposes, accurate measurements of medicines are crucial for patient safety.

To achieve accurate measurements, we use devices like measuring tapes for length, thermometers for temperature, weighing scales for weight, and measuring cups for volume. These tools are designed for specific measurements and help reduce errors, ensuring that the results are reliable and consistent.