Difference Between Mass and Weight

Q: Write two differences between mass and weight units?

SI unit for weight is kgms -2 or Newton(N). Other units are gcms -2 or dyne, lbfts -2 or poundal SI unit for mass is the kilogram (kg). Other units are gram(g), milligram(mg)

Q: Calculate the weight of a 5 kg object on a planet where acceleration due to gravity is 20ms-2.

Weight = Force = mg Substitute 5 kg for 'm', 20 ms -2 for 'g'. w=5×20 w=100 N

Difference Between Mass and Weight

Edited By Vishal kumar | Updated on Jul 02, 2025 04:28 PM IST

We habitually use the words mass and weight without knowing their difference. So, what is the difference between mass and weight? The terms 'mass' and 'weight' have different meanings and concepts in physics. It is important to understand the difference between these two terms. Mass is intrinsic property while weight is extrinsic property. This article discusses what is mass and weight, their units, dimensional formulas, and mass and weight differences.

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Mass
Weight
Equation Relating Mass and Weight
What is the Difference Between Mass and Weight
Mass Vs Weight

Difference Between Mass and Weight

Mass

A body's mass is an intrinsic attribute that measures its inertia. It measures how much resistance a body puts up when trying to change its state of motion. Mass and energy, according to Einstein's theory of relativity, are the same thing. Newton's second law is used to define mass mathematically. The amount of matter present in a thing is expressed by its mass. There can't be zero mass in a physical body.

SI Unit Of Mass

The SI unit of mass is $\mathrm{Kilogram}$. The other units of mass are milligrams and micrograms.

1 milligram is $\frac{1}{1,000,000}$

1 microgram is $\frac{1}{1,000,000,000}$

Dimensional Formula Of Mass

The dimensional formula of mass is $\left[M^1 L^0 T^0\right]$

Weight

The weight of a body is the amount of force exerted by a gravitational field (such as the Earth's gravity).

Weight $=F=m g$

Because a body's weight is determined by the effect of the gravitational field acting on it, a body of the same mass might have various weights in different areas. Even a huge object's weight can be zero.

SI unit Of Weight

The SI unit of weight is Newton($N$).

$$1 \mathrm{~N}=1 \mathrm{~kg} \cdot \mathrm{~m} / \mathrm{s}^2$$

Other units are dyne and kilogram-force.

1 dyne $=10^{-5}$ newtons

$1 \mathrm{kgf} \approx 9.8 \mathrm{~N}$

Dimensional Formula Of Weight

The dimensional formula for weight is $\left[M^1 L^0 T^0\right]$

Equation Relating Mass and Weight

Weight $(\mathrm{W})=$ Mass $(\mathrm{m}) \times$ Gravitational Acceleration $(\mathrm{g})$

$$
W=m g
$$

where,

Weight is the force exerted on the object by the gravity
Mass is the mass of an object
"g" is the acceleration due to gravity

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What is the Difference Between Mass and Weight

Although mass and weight are commonly used interchangeably in everyday situations, they refer to different quantities in physics. Mass and weight, on the other hand, are inextricably linked. Here we are going to distinguish between mass and weight. The amount of matter present in a thing is expressed by its mass. There can't be zero mass in a physical body. The gravitational field of another huge object exerts a force on any massive body. This force is referred to as weight. The mass of a thing determines its weight. When the gravitational field strength changes, a body's weight changes, but its mass remains constant. For example, an object's mass is the same on Earth and Mars, but its weight is different. So far, we have discussed two differences between mass and weight.

This image shows us different bodies with the same weight taken at places with different gravitational forces.

Identical weights on spring scales

Related Topics,

Mass Vs Weight

Mass and Weight Differences are as follows:

Property	Mass	Weight
Definition	When a force is applied to an item, its mass is defined by the amount of acceleration it experiences.	In a gravitational field, any object with mass experiences a gravitational force. The object's weight is the gravitational force.
Type of quantity	Mass is a fundamental or base quantity	Weight is a derived quantity.
Dimension	[M]	[MLT-2] weight has the dimension of force.
Type of Physical quantity	Mass is a scalar quantity. Since it only has magnitude and no direction.	Since force is a vector quantity, weight is also a vector quantity.
Units	SI unit: kilogram (kg) CGS unit: gram (g) FPS unit: pound (lb)	SI unit: $\mathrm{kg} \cdot \mathrm{ms}^{-2}$ or Newton Represented by (N) CGS unit: g.cms ${ }^{-2}$ or dyne Represented by (Dyn) FPS unit: $\mathrm{lb} \cdot \mathrm{ft} / \mathrm{s}^2$ or poundal Represented by (pdl)
Effect of gravity	Gravity does not affect mass because it is an intrinsic characteristic. If a physical body does not release or absorb energy in any form, its mass remains constant.	Because weight is related to gravitational acceleration, it fluctuates with the gravitational field.
Zero gravity condition	When a body is not in a gravitational field, its mass is not zero.	In a gravitational field with zero gravity, weight is zero. A body's weight is virtually zero, for example, during an ideal free fall or in space.
During the presence of other forces	According to the definition of mass, it does not depend on any force. So, it does not change in the presence of forces.	Weight changes in the presence of different kinds of forces. For example:Buoyant force acts on a body immersed in a fluid. This force changes the weight of the immersed body. Inside an accelerating lift, a person's weight can shift. If the acceleration is upwards, it becomes heavier, and if the acceleration is downwards, it becomes lighter. A body effectively becomes weightless during a free fall (downward acceleration equal to gravitational acceleration).
Instruments of measurement	Various balancing procedures can be used to determine mass. Weight can also be used to determine it. The mass of subatomic charged particles with very tiny masses is measured with the help of electric field and magnetic field.	A spring balance is commonly used to determine weight.

The above table has distinguished mass and weight thoroughly.

The Difference Between Mass And Weight With Examples

Inside a fluid, an object's weight may appear to increase or decrease, but its mass remains constant. Everything would be a little heavier in the absence of the Earth's atmosphere (but we wouldn't be alive to check that).

Neil Armstrong

Because the gravitational accelerations of different planets are not equal, objects weigh differently on different planets. (for example, an astronomer weighs less on the Moon than on the Earth).

The weight of an astronomer in space is zero.

Astronaut cosmonaut space suit model

Frequently Asked Questions (FAQs)

1. What is the difference between mass and weight in brief?

Mass is an intrinsic quantity, and weight is an extrinsic quantity.

Weight = Force = mg

2. Is weight a force?

Yes

3. What is the difference between charge and mass?

Not everything with mass has a charge, but a charge needs to have a mass.
The charge has two types, while mass has only one.
A Charged body have electrostatic force, while a body with mass has gravitational force.
Charges experience two nature of electrostatic force (repulsive and attractive) while gravitational force is only attractive.

4. Write two differences between mass and weight units?

SI unit for weight is kgms^-2 or Newton(N). Other units are gcms^-2 or dyne, lbfts^-2 or poundal

SI unit for mass is the kilogram (kg). Other units are gram(g), milligram(mg)

5. Calculate the weight of a 5 kg object on a planet where acceleration due to gravity is 20ms-2.

Weight = Force = mg

Substitute 5 kg for 'm', 20 ms^-2 for 'g'.

w=5×20

w=100 N

6. Why is the gravitational force between two objects proportional to their masses but not their weights?

The gravitational force between two objects is proportional to their masses because mass is an intrinsic property of matter. Weight, being the force of gravity on an object, is a result of this interaction, not a cause of it. The formula F = G(m1m2)/r² uses masses, not weights, to calculate gravitational force.

7. How does the relationship between mass and weight affect the design of space suits?

Space suits are designed considering both mass and weight. The suit's mass affects the astronaut's mobility and energy expenditure, which remains constant in space. However, the suit's weight on different celestial bodies varies, affecting things like joint design and the effort required for movement in different gravitational fields.

8. How does the equivalence principle in general relativity relate to mass and weight?

The equivalence principle states that the gravitational mass (which determines weight) is equivalent to the inertial mass (which resists acceleration). This principle suggests that the effects of gravity are indistinguishable from the effects of acceleration, linking the concepts of mass and weight in a profound way.

9. Why do some physics problems specify "massless ropes" or "massless pulleys"?

Specifying "massless" components in physics problems is a simplification that allows focus on the main objects of interest. It eliminates the need to account for the weight and rotational inertia of these components. This distinction highlights how mass (even when assumed to be zero) affects physical scenarios differently than weight.

10. How does the relationship between mass and weight affect the concept of "apparent weight" in an elevator?

In an elevator, your mass remains constant, but your apparent weight changes. When the elevator accelerates upward, you feel heavier because the floor pushes up on you with a force greater than your weight. During downward acceleration, you feel lighter. This demonstrates how acceleration can affect the force we perceive as weight, while mass remains unchanged.

11. Can an object's mass change? If so, under what circumstances?

An object's mass can change, but only if the amount of matter it contains changes. This can happen through processes like nuclear reactions (where mass is converted to energy), chemical reactions, or physical addition or removal of material. In everyday situations, an object's mass remains constant.

12. Why do physicists often use the term "rest mass" when discussing mass?

Physicists use "rest mass" to refer to an object's mass when it's not moving relative to the observer. This distinction is important in special relativity, where an object's observed mass increases as it approaches the speed of light. Rest mass remains constant and is the mass we typically refer to in everyday situations.

13. How do mass and weight affect an object's momentum differently?

Momentum is calculated as mass times velocity (p = mv). Mass directly affects momentum, while weight does not appear in the equation. An object's momentum would be the same on Earth or the moon (assuming the same velocity), despite the difference in weight, because the mass remains constant.

14. How does the concept of reduced mass in two-body problems relate to mass and weight?

Reduced mass is a calculated value used to simplify two-body problems in physics. It depends on the masses of the two objects, not their weights. This concept is useful in various scenarios, from atomic physics to celestial mechanics, and emphasizes the fundamental nature of mass in physical interactions.

15. How does the concept of mass-energy equivalence (E=mc²) relate to the difference between mass and weight?

Mass-energy equivalence (E=mc²) shows that mass and energy are interchangeable. This relates to mass as an intrinsic property of matter and energy. Weight, being a force due to gravity, is not directly addressed by this equation. However, the equation implies that adding energy to a system increases its mass and, consequently, its weight in a gravitational field.

16. Why does your weight change on different planets, but your mass remains the same?

Your mass remains constant because it's the amount of matter in your body, which doesn't change. However, weight is a force that depends on the strength of gravity, which varies between planets. So, your weight changes as the gravitational force changes, but your mass stays the same.

17. Can an object have mass but no weight?

Yes, an object can have mass but no weight in a zero-gravity environment, such as in space far from any significant gravitational field. The object still has mass (amount of matter), but it experiences no gravitational force, so its weight is zero.

18. How does the equation F = ma relate to mass and weight?

In the equation F = ma (Force = mass × acceleration), mass is directly involved. Weight is a specific type of force (W = mg, where g is gravitational acceleration). This shows that while mass is an inherent property, weight is a force resulting from mass in a gravitational field.

19. Why do we use kilograms for both mass and weight in everyday life?

In everyday situations on Earth, we often use kilograms for both because the gravitational acceleration is nearly constant on Earth's surface. This leads to a proportional relationship between mass and weight, making them seem interchangeable. However, scientifically, weight should be measured in newtons.

20. How would you explain the difference between mass and weight to a young child?

You could explain that mass is like how much "stuff" an object is made of, which doesn't change. Weight is how hard that "stuff" is pulled down by the Earth. On the moon, you'd have the same amount of "stuff" (mass), but you'd feel lighter because the moon doesn't pull as hard as Earth.

21. How does the distinction between mass and weight affect our understanding of black holes?

In black hole physics, mass is crucial as it determines the black hole's properties, including its event horizon. The concept of weight becomes less relevant near a black hole due to extreme gravitational effects. The mass-energy equivalence (E=mc²) becomes particularly important, as black holes can be described by their mass, angular momentum, and charge.

22. If you went to the moon, would you need to eat less food to maintain your weight?

No, you wouldn't need to eat less food on the moon to maintain your mass. While your weight would be about 1/6th of what it is on Earth due to lower gravity, your body's energy requirements are based on your mass and activity level, not your weight. Your caloric needs would remain largely the same.

23. How do bathroom scales measure mass if they're affected by gravity?

Bathroom scales actually measure weight (the force exerted by gravity on your mass), not mass directly. They are calibrated to display a mass value based on Earth's standard gravity. On other planets, the same scale would give different readings for the same mass due to different gravitational forces.

24. Why is the concept of "massless particles" challenging to understand in relation to weight?

Massless particles, like photons, challenge our understanding because they have no mass but still carry energy and momentum. They don't experience weight in a gravitational field the way massive particles do, but they are still affected by gravity through the curvature of spacetime, as described by general relativity.

25. Why is the concept of "weightlessness" in space misleading?

The term "weightlessness" in space is misleading because objects in orbit still have weight; they're just in a constant state of free fall. They experience gravity but are falling around the Earth at the same rate as their spacecraft, creating the illusion of weightlessness. Their mass, of course, remains unchanged.

26. What is the fundamental difference between mass and weight?

Mass is a measure of the amount of matter in an object, while weight is the force exerted on that mass due to gravity. Mass is constant regardless of location, but weight can change depending on the strength of the gravitational field.

27. What happens to an object's mass and weight in a vacuum?

In a vacuum, an object's mass remains unchanged because mass is an intrinsic property of matter. However, if the vacuum is also in a zero-gravity environment, the object's weight would become zero. If gravity is present, the weight remains unchanged from non-vacuum conditions.

28. How does the concept of inertia relate to mass but not weight?

Inertia, the resistance of an object to changes in its motion, is directly related to mass. An object with more mass has more inertia. Weight, being a force, doesn't determine an object's inertia. This is why objects in space, where they are weightless, still have inertia based on their mass.

29. Why is the kilogram the SI unit for mass but not for weight?

The kilogram is the SI unit for mass because mass is a fundamental property of matter. Weight, being a force, is measured in newtons in the SI system. Using kilograms for weight in everyday life is a convenience but not scientifically accurate.

30. How does buoyancy affect an object's weight but not its mass?

Buoyancy is an upward force exerted by fluids that opposes the weight of an immersed object. It affects the apparent weight of an object (making it seem lighter) but does not change its mass. The mass remains constant whether the object is in air, water, or any other fluid.

31. Why don't we feel the weight of the atmosphere pressing down on us?

We don't feel the weight of the atmosphere because our bodies evolved in this pressure, and we have internal pressure to counterbalance it. Also, the pressure acts equally in all directions, not just downward. This relates to the difference between mass and weight: the atmosphere has mass, but we don't perceive its weight directly.

32. Why is the term "zero-g" or "microgravity" more accurate than "zero gravity" for describing conditions in orbit?

"Zero-g" or "microgravity" are more accurate terms because objects in orbit are still under the influence of gravity. They are in a constant state of free fall, creating the illusion of weightlessness. The term "zero gravity" is misleading as gravity is still present; it's the perception of weight that's absent.

33. How does the concept of center of mass relate to the distribution of an object's mass versus its weight?

The center of mass is determined by the distribution of an object's mass, not its weight. It's the average position of mass in an object. While weight (the force due to gravity) acts at the center of mass, the center of mass itself is a property related to the object's mass distribution, regardless of the gravitational field it's in.

34. Why is the mass of subatomic particles often expressed in energy units (e.g., electron-volts) rather than mass units?

Expressing subatomic particle masses in energy units (like electron-volts) is a consequence of mass-energy equivalence (E=mc²). At the subatomic level, the interchangeability of mass and energy becomes significant. This practice emphasizes that mass is a form of energy, distinct from the force-based concept of weight.

35. How does the distinction between mass and weight affect our understanding of tidal forces?

Tidal forces arise from the difference in gravitational force across an object's extent, which relates to mass distribution, not weight. While weight is the total gravitational force on an object, tidal forces depend on how this force varies across the object's mass. This distinction is crucial in understanding phenomena like ocean tides and tidal locking of moons.

36. Why is the concept of mass important in particle physics, while weight is rarely mentioned?

In particle physics, mass is a fundamental property of particles, determining their behavior in interactions and their role in the Standard Model. Weight, being a force due to gravity, is less relevant at the subatomic scale where other forces (strong, weak, electromagnetic) dominate. The focus on mass highlights its importance as an intrinsic property of matter.

37. How does the relationship between mass and weight affect the design and function of accelerometers?

Accelerometers measure proper acceleration (acceleration relative to free fall) rather than coordinate acceleration. They essentially measure the force on a known mass, which is related to weight but varies with acceleration. This demonstrates how the mass-weight relationship is crucial in inertial measurement devices.

38. Why is the concept of relativistic mass considered outdated, and how does this relate to the mass-weight distinction?

The concept of relativistic mass (mass increasing with velocity) is considered outdated because it can lead to confusion. Modern physics prefers to keep mass (rest mass) constant and account for relativistic effects in energy and momentum. This approach maintains a clearer distinction between the intrinsic property of mass and the force-based concept of weight.

39. How does the principle of equivalence in general relativity challenge our classical notions of mass and weight?

The principle of equivalence states that gravitational mass (responsible for weight) is equivalent to inertial mass (resistance to acceleration). This principle blurs the distinction between gravity and acceleration, suggesting that weight (traditionally viewed as a force) might be more fundamentally related to the curvature of spacetime, which is linked to mass distribution.

40. Why is the concept of mass important in quantum mechanics, despite the absence of classical notions of weight?

In quantum mechanics, mass remains a fundamental property of particles, affecting their behavior through the Schrödinger equation and determining properties like de Broglie wavelength. Weight, as a classical force concept, doesn't directly appear in quantum formulations. This emphasizes mass as an intrinsic property independent of gravitational context.

41. How does the relationship between mass and weight affect our understanding of neutron stars?

Neutron stars have enormous mass compressed into a small volume, resulting in extreme gravitational fields. While the mass of a neutron star determines its properties and behavior, the concept of weight becomes less applicable due to the extreme conditions. This scenario highlights the fundamental nature of mass in astrophysics, distinct from the Earth-bound concept of weight.

42. Why is the kilogram the only SI base unit still defined by a physical artifact, and how does this relate to mass and weight?

Until recently, the kilogram was defined by a physical artifact because mass is a fundamental property that was challenging to define in terms of natural constants. This definition focused on mass, not weight, emphasizing the primacy of mass as a base quantity. In 2019, it was redefined in terms of the Planck constant, further distinguishing it from the force-based concept of weight.

43. How does the concept of gravitational time dilation relate to mass and weight?

Gravitational time dilation, where time passes slower in stronger gravitational fields, is directly related to mass (which curves spacetime) rather than weight. An object's weight (the force it experiences) doesn't cause time dilation, but the mass of the object creating the gravitational field does. This illustrates how mass, not weight, is fundamental in general relativity.

44. Why is the concept of mass gap important in particle physics, and how does it differ from considerations of weight?

The mass gap in particle physics refers to the minimum mass that particles of a quantum field theory must have. This concept is crucial for understanding the behavior of particles and forces. It deals with the intrinsic property of mass, independent of gravitational effects or weight, highlighting the fundamental role of mass in particle physics.

45. How does the relationship between mass and weight affect our understanding of dark matter?

Dark matter is inferred to exist primarily through its gravitational effects, which are determined by its mass, not its weight. The concept of dark matter emphasizes the distinction between mass (which it must have to exert gravitational influence) and weight (which is not directly observable for dark matter). This underscores how mass, not weight, is the key property in cosmological theories.

46. Why is the concept of mass defect important in nuclear physics, and how does it relate to the mass-weight distinction?

Mass defect in nuclear physics refers to the difference between the mass of an atomic nucleus and the sum of its constituent nucleons. This difference, converted to energy via E=mc², explains nuclear binding energy. This concept deals purely with mass, not weight, emphasizing how fundamental mass is in understanding nuclear processes and energy release.

47. How does the relationship between mass and weight influence the design of planetary rovers?

In designing planetary rovers, engineers must consider both mass and weight separately. The rover's mass affects its inertia and the energy required to move it, which remains constant regardless of the planet. However, its weight will vary depending on the planet's gravity, affecting traction, stability, and power requirements. This distinction is crucial for creating rovers that can operate effectively in different gravitational environments.

48. Why is the concept of reduced Planck constant (ℏ) important in quantum mechanics, and how does it relate to mass rather than weight?

The reduced Planck constant (ℏ) is crucial in quantum mechanics, appearing in fundamental equations like the Schrödinger equation. It relates to particle properties like angular momentum and is used in defining quantities like the Compton wavelength, which depends on a particle's mass. The focus on ℏ and mass, rather than weight, in quantum mechanics highlights the fundamental nature of mass in describing quantum phenomena.

49. How does the distinction between mass and weight affect our understanding of buoyancy and Archimedes' principle?

Archimedes' principle states that the buoyant force on an object is equal to the weight of the fluid displaced. While this principle involves weight, it's the object's mass (and volume) that determines how much fluid it displaces. This illustrates how mass is the intr