Mass and Weight
Complete Notes with Important Points and Fact-Based Questions
Introduction
Mass and weight are two important concepts in physics that are frequently asked in competitive examinations such as SSC, JKSSB, Railway, Banking, UPSC, NEET, and State Exams. Although people often use these terms interchangeably in daily life, scientifically they are different.
Mass tells us the amount of matter present in a body, while weight is the gravitational force acting on that body.
What is Mass?
Mass is the quantity of matter contained in a body.
It measures the inertia of an object, which means resistance to change in motion.
Formula Related to Mass
m = \frac{F}{a}
Where:
m = Mass
F = Forcea = Acceleration
Characteristics of Mass
| Characteristic | Description |
|---|---|
| Scalar Quantity | Has magnitude only |
| Constant Quantity | Remains same everywhere |
| SI Unit | Kilogram (kg) |
| Measured By | Beam balance |
| Depends On | Amount of matter |
What is Weight?
Weight is the force with which Earth attracts a body toward its center.
It depends upon gravity.
Formula of Weight
W = mg"
Where:
W = Weight
m = Massg = Acceleration due to gravity
Characteristics of Weight
| Characteristic | Description |
|---|---|
| Vector Quantity | Has magnitude and direction |
| Variable Quantity | Changes from place to place |
| SI Unit | Newton (N) |
| Measured By | Spring balance |
| Depends On | Gravity |
Difference Between Mass and Weight
| Mass | Weight |
|---|---|
| Amount of matter | Gravitational force |
| Scalar quantity | Vector quantity |
| Constant everywhere | Changes with gravity |
| Measured in kilogram | Measured in Newton |
| Measured by beam balance | Measured by spring balance |
| Never zero | Can become zero in space |
Relation Between Mass and Weight
Weight depends directly on mass.
If mass increases, weight also increases.
Mathematical Relation
W = mg"
On Earth:
g ≈ 9.8 m/s²
Acceleration Due to Gravity
Gravity is the force by which Earth attracts objects.
Value of g
| Place | Value of g |
|---|---|
| Earth | 9.8 m/s² |
| Moon | 1.63 m/s² |
Weight on the Moon becomes approximately one-sixth of weight on Earth.
Why Mass Remains Constant?
Mass depends on the amount of matter present in an object, which does not change with location.
Example:
A person with mass 60 kg on Earth will still have mass 60 kg on the Moon.Why Weight Changes?
Weight depends on gravity.
Different planets and celestial bodies have different gravitational forces.
Example:
A person weighing 600 N on Earth will weigh much less on the Moon.Weightlessness
Weightlessness is the condition in which the apparent weight of a body becomes zero.
Examples
Astronauts inside spacecraft
Free-falling liftApplications of Mass and Weight
| Field | Application |
|---|---|
| Space Science | Satellite calculations |
| Engineering | Machine design |
| Transportation | Load calculations |
| Sports | Weight categories |
| Medical Science | Body measurements |
Important Points for Exams
Mass is scalar quantity.
Weight is vector quantity.SI unit of mass = kilogram.
SI unit of weight = Newton.
Mass remains constant everywhere.
Weight changes with gravity.
Weight on Moon is one-sixth of Earth.
Beam balance measures mass.
Spring balance measures weight.
Astronauts experience apparent weightlessness in space.
Common Examples
Example 1
A person has:
Mass = 50 kg
Weight on Earth:
W = 50 \times 9.8
Weight = 490 N
Example 2
On Moon:
W = 50 \times 1.63
Weight ≈ 81.5 N
Frequently Asked Questions (FAQs)
Q1. What is mass?
Mass is the amount of matter present in a body.
Q2. What is weight?
Weight is the gravitational force acting on a body.
Q3. Why does weight change from place to place?
Because gravity changes from place to place.
Q4. Why does mass remain constant?
Because amount of matter does not change.
Q5. What is the SI unit of mass?
Kilogram (kg)
Q6. What is the SI unit of weight?
Newton (N)
Q7. Which instrument measures mass?
Beam balance.
Q8. Which instrument measures weight?
Spring balance.
Q9. Why do astronauts float in space?
Due to apparent weightlessness.
Q10. What happens to weight on the Moon?
It becomes nearly one-sixth of Earth’s weight.
Fact-Based MCQs
1. The SI unit of mass is:
A. Newton
B. Joule
C. Kilogram
D. Pascal
✅ Answer: C
2. Weight is a:
A. Scalar quantity
B. Vector quantity
C. Fundamental quantity
D. Dimensionless quantity
✅ Answer: B
3. Which instrument measures weight?
A. Beam balance
B. Physical balance
C. Spring balance
D. Meter scale
✅ Answer: C
4. Mass of an object on the Moon is:
A. Zero
B. Half
C. Double
D. Same as on Earth
✅ Answer: D
5. Weight depends upon:
A. Density
B. Gravity
C. Volume
D. Shape
✅ Answer: B
6. Weight on Moon is approximately:
A. Equal to Earth
B. Half of Earth
C. One-sixth of Earth
D. Double of Earth
✅ Answer: C
7. Which of the following is constant everywhere?
A. Weight
B. Gravity
C. Mass
D. Pressure
✅ Answer: C
Statement-Based Questions
Question 1
Consider the following statements:
Mass is a scalar quantity.
Weight depends upon gravity.
Mass changes from Earth to Moon.
Choose the correct option:
A. Only 1 and 2
B. Only 2 and 3
C. Only 1 and 3
D. 1, 2 and 3
✅ Answer: A
Question 2
Which of the following statements are correct?
Weight is measured in Newton.
Spring balance measures mass.
Weight can become zero in space.
A. Only 1 and 2
B. Only 1 and 3
C. Only 2 and 3
D. 1, 2 and 3
✅ Answer: B
Question 3
Consider the following facts:
Weight is a force.
Mass measures inertia.
Beam balance measures weight.
A. Only 1 and 2
B. Only 2 and 3
C. Only 1 and 3
D. 1, 2 and 3
✅ Answer: A
Assertion–Reason Questions
Assertion (A)
Mass remains constant everywhere.
Reason (R)
Mass depends upon amount of matter.
A. Both A and R are true and R explains A
B. Both true but R not explanation
C. A true, R false
D. A false, R true
✅ Answer: A
Assertion (A)
Weight becomes less on the Moon.
Reason (R)
Gravity on the Moon is weaker than on Earth.
A. Both A and R are true and R explains A
B. Both true but R not explanation
C. A true, R false
D. A false, R true
✅ Answer: A
Quick Revision Table
| Quantity | Mass | Weight |
|---|---|---|
| Definition | Amount of matter | Gravitational force |
| Nature | Scalar | Vector |
| SI Unit | kg | Newton |
| Constant/Variable | Constant | Variable |
| Instrument | Beam balance | Spring balance |
Conclusion
Mass and weight are fundamental concepts of mechanics. Understanding their differences, formulas, units, and applications is essential for solving conceptual and numerical questions in competitive examinations. Questions related to weightlessness, gravity, SI units, and instruments are frequently repeated in exams.
Prepared By Home Academy