Mass vs Weight in Physics: Formula, Table, and Daily Life Examples
The difference between mass and weight is a common conceptual challenge in JEE Main Physics, but mastering it ensures strong fundamentals for mechanics. Mass represents the amount of matter in a body and always remains constant, whereas weight is the gravitational force acting on that mass, changing with the value of gravitational acceleration. Many students confuse these properties, especially in calculations or real-world scenarios, so clarity is vital for both theory and numerical questions.
Difference Between Mass and Weight: Physics Foundations
In physics, mass (symbol: m) refers to the measure of matter contained in an object. It is a scalar quantity and does not depend on direction. The SI unit of mass is the kilogram (kg), and it remains unchanged regardless of location—on Earth, the Moon, or in deep space.
Weight (symbol: W) is the force exerted by gravity on an object. It is a vector quantity, directed towards the center of the gravitating body (like Earth). SI unit of weight is the newton (N). Weight is calculated using the formula W = m × g, where g is the acceleration due to gravity (approximately 9.8 m/s2 on Earth). Changing the value of g changes the weight but not the mass.
- Mass is constant for a body everywhere.
- Weight varies according to gravity at different locations.
- Mass is measured using a beam or pan balance.
- Weight is measured using a spring balance.
- Mass is a fundamental property, while weight is derived.
Tabular Difference Between Mass and Weight
| Property | Mass | Weight |
|---|---|---|
| Definition | Amount of matter in a body | Force due to gravity on mass |
| Nature | Scalar quantity | Vector quantity |
| SI Unit | kg | N |
| Symbol | m | W |
| Formula | – | W = m × g |
| Value on Moon (1/6 g) | Same as on Earth | One-sixth of Earth value |
| Instrument | Beam balance | Spring balance |
| Can be zero? | No—for material objects | Yes—in zero gravity |
| Change with location? | Remains constant | Changes with gravity |
| Fundamental / Derived? | Fundamental | Derived |
Examples: Calculating Mass and Weight for JEE Main
Suppose a stone has a mass m = 2 kg. On Earth (“g ≈ 9.8 m/s2”), its weight is W = m × g = 2 × 9.8 = 19.6 N.
On the Moon, where g ≈ 1.6 m/s2, WMoon = 2 × 1.6 = 3.2 N. So, mass remains 2 kg, but weight drops to 3.2 N due to the lower value of gravity.
- Weight on Jupiter would be much higher due to greater acceleration due to gravity.
- Mass remains constant in all planetary or space locations.
- In orbit, almost “weightless” conditions appear, though mass is still present.
- Spring balances directly measure weight; beam balances compare mass.
- Always use SI units (kg for mass, N for weight) in JEE answers.
Practice such differences using units and measurement notes and JEE laws of motion summary for clarity on vector and scalar properties.
Common Pitfalls and Exam Traps in the Difference Between Mass and Weight
- Confusing kilograms as a unit of weight—in SI, only newton is weight.
- Ignoring g’s variation at different places (Earth, Moon, other planets).
- Assuming weighing machines give direct mass; most show weight, calibrated for Earth’s g.
- Missing that mass cannot be zero for any matter, but weight can be zero in space.
- Mixing up scalar and vector nature—always state direction for forces like weight.
For deeper understanding, read about gravitation and acceleration due to gravity. See how force and units and dimensions apply in real calculations.
- Review Newton’s laws of motion for the connection between mass, force, and acceleration.
- Check scalar and vector explanations for exam questions.
- Build accuracy on density and specific gravity, often linked with mass calculations.
- Use units and measurements mock test to practice SI usage.
You can further strengthen your command over the difference between mass and weight by solving questions from JEE Main revision notes and reviewing key worked examples in Vedantu study resources.
- Always define all symbols in your JEE answers.
- Emphasize the formula W = m × g and units.
- Separate scalar vs. vector for maximum marks.
Vedantu learning materials deliver exam-structured notes on this topic, providing real clarity for JEE. With practice, the distinction between mass and weight becomes intuitive, preventing common mistakes. For every calculation, ensure you check both mass and weight units, and remember, only weight changes with location, not mass.
FAQs on Difference Between Mass and Weight: Definitions, Examples, and FAQs
1. What is the main difference between mass and weight?
Mass is the amount of matter in an object, whereas weight is the force exerted on that object due to gravity.
Main points:
- Mass is measured in kilograms (kg); weight is measured in newtons (N).
- Mass does not change with location; weight changes if gravity changes (e.g., on the Moon).
- Weight is calculated as weight = mass × gravitational acceleration (g).
2. How does gravity affect weight but not mass?
Gravity directly impacts weight but leaves mass unchanged.
Details:
- Mass is a measure of matter and remains constant everywhere.
- Weight is the result of mass × gravity (g), so it fluctuates with the strength of gravitational pull.
- For example, your weight is less on the Moon because the Moon’s gravity is weaker than Earth’s.
3. Which unit is used for mass and which for weight?
Mass is measured in kilograms (kg), while weight is measured in newtons (N).
- SI unit of mass: kg
- SI unit of weight: N (newton), which is equivalent to kg·m/s²
4. Why are mass and weight often confused?
People confuse mass and weight because both are sometimes referred to as 'weight' in daily life and both relate to the size or amount of something.
Reasons include:
- We ‘weigh’ objects using scales that actually measure force (weight), but display mass (kg).
- In everyday conversation, 'weight' is used instead of 'mass.'
- Common confusion between units (kg for mass vs. N for weight).
5. How do you explain mass and weight to a child?
Mass is how much stuff (matter) is inside something, while weight is how hard gravity pulls on that stuff.
- If you go to the Moon, your mass stays the same, but your weight is much less because gravity is weaker.
- Mass is like what fills a backpack; weight is how heavy the backpack feels when you lift it.
6. What are 5 differences between mass and weight?
The five main differences between mass and weight are:
- Definition: Mass is the amount of matter; weight is the gravitational force on that matter.
- Unit: Mass (kg); weight (N).
- Constancy: Mass is constant; weight varies with gravity.
- Type: Mass is scalar; weight is vector.
- Instrument: Mass is measured by a beam balance; weight by a spring balance.
7. Which is measured directly by a weighing scale: mass or weight?
A weighing scale measures the weight (force due to gravity) but is usually calibrated to display mass in kilograms.
- Weighing scales use gravitational force to give a reading.
- Electronic balances convert this force into a mass value based on standard gravity (9.8 m/s²).
- On the Moon, a scale would show a lower value for the same object if using the local gravity.
8. Is body weight mass or weight?
Technically, your body weight is a measure of the force gravity exerts on your body mass. In daily speech, people use 'weight' to mean 'mass,' but:
- Mass is what you have; weight is how much gravity acts on it.
- On a different planet, your mass remains constant but your weight would change.
9. Why does your weight change on the Moon but mass remains the same?
Your weight changes on the Moon due to reduced gravity, but your mass (amount of matter) does not change.
- The Moon’s gravity is about 1/6th of Earth’s.
- Mass is a fundamental property of matter and stays constant.
- Weight = mass × gravity, so less gravity means less weight.
10. Can mass and weight ever be equal?
No, mass (kg) and weight (N) are different physical quantities and units, so they cannot be numerically equal except by coincidence.
- Mass measures matter; weight is mass × gravitational acceleration.
- For mass and weight to have equal numerical values, the value of gravity (g) would need to be 1, which is not true on Earth or any other planet.
11. What happens to an object’s weight and mass in space?
In space, an object’s mass remains the same, but its weight becomes nearly zero because gravity is extremely weak.
- Mass is always constant wherever the object is.
- Weight depends on the gravitational pull, which is almost absent in deep space, making the object "weightless."
