The amount of matter contained in a body is called its mass.
The measure of the quantity of matter in a body is called its mass.
The mass of a body is a scalar quantity. It is independent of surroundings and the position of the body. It is a constant quantity for a given body.
Mass is measured in kilograms (kg) in the SI system.
- This means that regardless of the location or surroundings of the body, its mass will not change.
- Mass is independent of the shape and size of the body, as well as the presence of other bodies nearby.
- Unlike vector quantities, such as velocity or force, mass is a scalar quantity that only has magnitude and no direction.
- Therefore, option B is the correct answer as it accurately describes the characteristic of mass mentioned in the passage.
The force with which a body is attracted by the earth is known as the weight of the body.
When the earth attracts a body with a gravitational force, the body accelerates towards the earth with an acceleration due to gravity (g). Thus, the force with which body of mass m is attracted by the earth is given by
F = ma = m × g = mg
This force is known as the weight of the body. The weight of a body is denoted by W.
∴ Weight, W = mg
Weight has both magnitude and direction. Hence weight is a vector quantity.
Unit of Weight: SI unit of weight is the same as that of the force i.e., newton (N).
Weight of the body is given by W = mg. So the weight of a body depends upon (i) the mass of the body and (ii) value of acceleration due to gravity.
The mass of a body remains the same throughout the universe, but the value of 'g' is different places. Hence the weight of a body is different at different place.
- The mass of a body remains the same at all places, so Option B is incorrect.
- The mass of a body is a scalar quantity, so Option C is incorrect.
- The mass of a body is measured in kilograms, as stated in the passage, so Option D is correct.
- Mass is a fundamental property of matter and does not change with location or surroundings. The SI unit for mass is kilograms (kg).
|1||The quantity of matter contained in a body is|
called the mass of the body.
|The force with which the earth attracts a body towards its centre is called the weight|
of the body.
|2||Mass of a body remains constant.||Weight of a body changes from place to|
|3||Mass of a body is never zero.||Weight of a body at the centre of the earth is|
|4||Mass is scalar quantity.||Weight is a vector quantity.|
|5||Mass is a measured in kg.||Weight is measured in kg wt or N.|
|6||Mass is measured by a beam balance.||Weight is measured by a weighing machine|
or a spring balance.
In SI, the weight is also measured in kg f or kg wt. Therefore, kilogram force or kilogram weight is force with which a mass of 1 kg is attracted by centre of earth.
1 kg f = 1 kg wt = 1 kg × 9.8 m/s2 = 9.8 kg ms-2 = 9.8 N
1 kg f = 9.8 N
In CGS, the practical unit of weight is grams force or g wt or 1g f or 1g wt is force with which a mass of 1g is attracted by the centre of the earth.
g = 9.8 ms-2
g = 9.8 × 100 cm/s2
1 g f = 1 g wt = 1 g × 980 cm s-2 = 980 dyne
1 g f = 980 dyne
Thrust: Force acting normally on a surface is called the thrust.
Thrust is a vector quantity and is measured in the unit of force, i.e., newton (N).
Pressure: The thrust acting on unit area of the surface is called the pressure.
If a thrust F acts on a area A, then pressure
Pressure is directly proportional to the force.
Pressure in inversely proportional to the area.
- Mass is an intrinsic property of matter and is independent of external factors.
- Mass is measured in kilograms (kg) in the SI system.
- The quantity of matter contained in a body determines its mass.
- The mass of a body can be measured using a beam balance.
- The masses of objects or bodies can be added algebraically.
- In contrast to weight, which depends on the force of gravity, mass remains constant in all situations.
Ex. A sharp knife cuts easily than a blunt knife by applying the same force.
Ex. A sharp needle pressed against our skin pierces it. But a blunt object with a wider contact area does not affect the skin when pressed against it with the same force.
The SI unit of pressure is called pascal (Pa) in honour of Blaise Pascal.
I Pa = 1 N/m2
One pascal is defined as the pressure exerted on a surface area of 1 m2 by a thrust of 1 N (acting normally on it).
Other units of pressure are bar and millibar are
1 bar = 105 N/m2 and 1 millibar = 102 N/m2
It is a common practice in meteorology to measure atmospheric pressure in bars and millibars. Further,
1 atmospheric pressure (1 atm) = 101·3 k Pa = 1·013 bar = 1013 m bar
- This unit is derived from the SI unit of pressure, pascal (Pa).
- 1 millibar is equal to 102 N/m2.
- It is a standard practice in meteorology to express atmospheric pressure in millibars.
- This allows for easier comparison and analysis of pressure values in weather forecasting and analysis.
Density of a substance is defined as its mass per unit volume.
Unit of density :- Since mass (M) is measured in kilogram (kg) and the volume (V) is measured in metre3 (m3), the unit of density is kg/m3. In cgs system, the unit of density is g cm–3.
These units are related as : 1 g cm–3 = 1000 kgm–3.
|1. What is the difference between mass and weight?|
|2. How can mass and weight be measured?|
|3. What is thrust and how is it related to weight?|
|4. What is pressure and how is it different from thrust?|
|5. How is density related to mass and weight?|