Unit of Force - Definition, Unit, Types, Formula, FAQs

Q: Differentiate between dyne and Newton units of force.

Dyne Newton It is the unit of force in CGS (Centimeter – gram – second) system of units. It is the unit of force in SI (System International ) system of units. Its symbol is dyn Its newton symbol is N 1 dyne is defined as the force required to accelerate 1 gram of mass at an acceleration of 1 centimeter per second squared 1 Newton is defined as the force required to accelerate 1 kg of mass at an acceleration of 1 meter per second squared.

Edited By Vishal kumar | Updated on Jul 02, 2025 04:39 PM IST

What is unit?
The quantity which can be used as a standard of measurement is known as unit. For example: If we say, the length of the rod is 2 meter, then the numerical value is 2 and the unit of the length is meter.

What is the unit of force? Define SI unit of force.

As we know force is a physical quantity, it has to be measured. To measure any physical quantity, there is a standard of measurement known as unit of that quantity.

The term force is discovered and defined by Isaac Newton SI unit, that’s why the unit of force is named after him which is NEWTON. However, force measurement units can differ, depending upon the different systems of measurements such as C.G.S. , M.K.S which we read further in this article.

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Unit of Force - Definition, Unit, Types, Formula, FAQs

SI unit of force in physics

SI unit stands for System International unit. This system of the unit consists of seven basic units which are used to derive other units.

The SI unit of force is kg m/sec² which is termed, Newton.

Derivation of SI unit of force in physics

To derive the SI unit of force in physics, we need to remember the formula of force which is defined as

F= m× a

where F ? Force

m ? Mass

a ? Acceleration

First, we derive the SI unit of acceleration using its formula which is defined as

a=∆v/∆t

where ∆v ? Change in velocity

∆t ? Change in time

Now, we write the SI unit of velocity and time in the formula of acceleration

a=m/s²

Hence, the SI unit of acceleration

a= msec^-2

Now, we put the SI unit of acceleration and mass in the formula of force

F= kg× msec^-2

Hence, the SI unit of force is given as

F= kg msec^-2 or Newton

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Other unit of force
Other than SI unit, force is also measured in different units depending upon the system of measurements which are given below :

Dyne ?

Symbol - dyn

1 dyn=10^-5N

1 dyne is defined as the force can be measured by required accelerate of 1 gram of mass at an acceleration of 1 centimeter per second. It is the unit of force in CGS (Centimeter – gram – second ) system of units and it is primarily used in measuring surface tension.

Gram- force ?

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Symbol - gf

1 gf=0.0098 N

1 gram- force is defined as the force required to accelerate 1 gram of mass at acceleration equal to the acceleration due to gravity. It is the gravitational unit of force in CGS (Centimeter – gram – second ) system of units.

Poundal ?

Symbol - pdl

1 pdl= 0.1382 N

1 Poundal is defined as the force required to accelerate 1 pound of mass at an acceleration of 1 foot per second. It is the unit of force in the FPS ( Foot – pound – second ) system of units and this system is commonly used in civil engineering and construction engineering.

Also read :

Pound- force ?

Symbol - lbf

1 lbf=4.448222 N

1 pound force is defined as the force required to accelerate 1 pound of mass at an acceleration equal to the acceleration due to gravity. It is the unit of force in FPS ( Foot – pound – second ) system of units and this is also used in civil engineering and construction engineering.

Kilogram-force ?

Symbol - kgf

1 kgf=9.806650 N

1 Kilogram-force is defined as the force required to accelerate 1 kilogram of mass at an acceleration equal to the acceleration due to gravity. It is the unit of force in MKS ( Meter – kilogram – second ) system of units and this system is also known as metric system.

Sthène ?

Symbol - sn

1 sn= 1000 N

1 Sthène is defined as the force required to accelerate 1 metric ton (1000 Kilograms) of mass at an acceleration of 1 meter per second. It is the unit of force in MTS ( metre–tonne–second ) system of units.

Kip ?

Symbol - kip

1 kip= 4.44822 kN

1 kip is defined as 1000 pound-force. It is used in engineering, primarily in civil engineering to measure engineering loads.

Also check-

NCERT Physics Notes:

Frequently Asked Questions (FAQs)

1. Define unit and write SI unit of force ?

The standard of measurement of a physical quantity is known as unit. The SI unit of force is kg m/sec^2 which is termed as Newton.

2. What are the various units of force?

Other than the SI unit that is Newton, force is also measured in other units. Some of them are

Dyne
Gram – force
Poundal
Pound – force
Kilogram – force
Sthène

3. Define 1 dyne of force.

1 dyne is defined as the force required to 1 gram of mass at an acceleration of 1 centimeter per second squared. It is the unit of force in CGS ( Centimeter – gram – second ) system of units.

4. Derive the unit of force in SI system.

To derive the SI unit of force, we write the SI unit of other physical quantities in the formula of force which is

F= m× a

where, m - Mass

a - Acceleration

So, F= kg× msec^{-2}

[ As SI unit of acceleration is msec2 and SI unit of mass is kg ]

or Newton

Hence derived unit of force or the SI unit of force is Newton

5. Differentiate between dyne and Newton units of force.

Dyne	Newton
It is the unit of force in CGS (Centimeter – gram – second) system of units.	It is the unit of force in SI (System International ) system of units.
Its symbol is dyn	Its newton symbol is N
1 dyne is defined as the force required to accelerate 1 gram of mass at an acceleration of 1 centimeter per second squared	1 Newton is defined as the force required to accelerate 1 kg of mass at an acceleration of 1 meter per second squared.

6. What is the SI unit of force?

The SI unit of force is the Newton (N). One Newton is defined as the force required to accelerate a mass of 1 kilogram at a rate of 1 meter per second squared (1 N = 1 kg⋅m/s²).

7. What is the relationship between force, mass, and acceleration?

The relationship between force, mass, and acceleration is described by Newton's Second Law of Motion: F = ma, where F is the net force, m is the mass, and a is the acceleration. This equation shows that force is directly proportional to both mass and acceleration.

8. Why is force considered a vector quantity?

Force is a vector quantity because it has both magnitude (strength) and direction. This means that to fully describe a force, you need to specify not only how strong it is but also which way it's acting.

9. How does mass differ from weight?

Mass is a measure of the amount of matter in an object and remains constant regardless of location. Weight, on the other hand, is the force exerted on an object due to gravity and can vary depending on the strength of the gravitational field.

10. What is force in physics?

Force is a push or pull acting on an object. It can cause an object to start moving, stop moving, or change its speed or direction. Force is a vector quantity, meaning it has both magnitude and direction.

11. How does friction affect the motion of objects?

Friction is a force that opposes the relative motion of objects in contact. It can slow down or stop moving objects, prevent stationary objects from starting to move, and generate heat. Without friction, many everyday activities would be impossible.

12. What is the normal force and when does it occur?

The normal force is a contact force that occurs when two surfaces are in contact. It acts perpendicular to the surface of contact and balances out other forces to prevent objects from sinking into each other. For example, when you stand on the floor, the normal force from the floor balances your weight.

13. How does air resistance affect falling objects?

Air resistance is a force that opposes the motion of objects through air. For falling objects, it acts upward, opposing the downward force of gravity. This causes objects to reach a terminal velocity, where the air resistance equals the gravitational force, resulting in constant speed.

14. What is tension force and where do we encounter it?

Tension force is the force transmitted through a string, rope, cable, or wire when it is pulled tight by forces acting from opposite ends. We encounter tension in many situations, such as in elevator cables, bridge support cables, and when pulling objects with ropes.

15. How does the concept of inertia relate to force?

Inertia is an object's resistance to change in its state of motion. It's directly related to the object's mass. Force is required to overcome inertia and change an object's motion. The more inertia an object has, the more force is needed to change its motion.

16. Can a force exist without causing motion?

Yes, a force can exist without causing motion. For example, when you push against a wall, you're exerting a force, but the wall doesn't move. This is because the wall exerts an equal and opposite force back on you, resulting in no net force and no motion.

17. What is the difference between contact and non-contact forces?

Contact forces require physical touch between objects to occur (e.g., friction, normal force), while non-contact forces can act at a distance without physical contact (e.g., gravity, electromagnetism).

18. What is centripetal force and how does it relate to circular motion?

Centripetal force is a force that acts on a body moving in a circular path, directed toward the center around which the body is moving. It causes the object to follow a curved path and is always directed perpendicular to the motion of the body and toward the fixed point of the center of the curve.

19. How do balanced and unbalanced forces affect an object's motion?

Balanced forces result in no change in an object's motion (it remains at rest or continues moving at constant velocity). Unbalanced forces cause a change in the object's motion, resulting in acceleration, deceleration, or a change in direction.

20. What is the difference between static and kinetic friction?

Static friction is the force that prevents an object at rest from starting to move, while kinetic friction is the force that resists the motion of an object already in motion. Static friction is typically greater than kinetic friction for the same surfaces.

21. How does gravity differ from other forces?

Gravity is a fundamental force of nature that attracts any two masses in the universe. Unlike many other forces, it's always attractive, never repulsive, and acts over vast distances. It's also much weaker than other fundamental forces but dominates on cosmic scales due to its long range and inability to be shielded.

22. How do forces combine when multiple forces act on an object?

When multiple forces act on an object, they combine vectorially to produce a net force. This means that both the magnitude and direction of each force must be considered. Forces in the same direction add, while forces in opposite directions subtract.

23. How does the normal force change when an object is on an inclined plane?

On an inclined plane, the normal force is less than the object's weight. It's equal to the component of the weight perpendicular to the plane's surface. As the angle of inclination increases, the normal force decreases, while the component of weight parallel to the plane (causing sliding) increases.

24. How do forces affect energy?

Forces can transfer energy between objects or convert energy from one form to another. When a force does work on an object, it changes the object's energy. For example, the gravitational force can convert potential energy to kinetic energy as an object falls.

25. What is the difference between conservative and non-conservative forces?

Conservative forces, like gravity, depend only on the initial and final positions of an object, not the path taken. Work done by conservative forces is path-independent. Non-conservative forces, like friction, depend on the path and typically convert mechanical energy to other forms, like heat.

26. How do forces manifest at the atomic and subatomic levels?

At atomic and subatomic levels, forces manifest as fundamental interactions: strong nuclear force, weak nuclear force, electromagnetic force, and gravity. These forces govern particle interactions and are responsible for the stability of matter and various physical phenomena at quantum scales.

27. How does the concept of force apply in quantum mechanics?

In quantum mechanics, the classical concept of force is replaced by potential energy functions and probability distributions. Forces are described in terms of interactions between particles, often represented by exchange of virtual particles. The uncertainty principle also affects how precisely we can measure forces at quantum scales.

28. How do forces contribute to the stability or instability of systems?

Forces play a crucial role in system stability. Balanced forces create stable equilibrium, while unbalanced forces can lead to instability. In more complex systems, the interplay of multiple forces can create stable, unstable, or metastable states, which is important in understanding phenomena from atomic structures to celestial mechanics.

29. What is the connection between force and field theories in physics?

Field theories in physics describe forces as the result of field interactions. For example, the gravitational force is described as the result of mass interacting with the gravitational field, and electromagnetic forces arise from charges interacting with electromagnetic fields. This concept unifies the treatment of forces acting at a distance.

30. How does the principle of superposition apply to forces?

The principle of superposition states that when multiple forces act on an object, the net force is the vector sum of all individual forces. This principle allows us to analyze complex force systems by breaking them down into simpler components and then combining their effects.

31. What is the significance of fictitious forces in non-inertial reference frames?

Fictitious forces, like the centrifugal force, appear in non-inertial (accelerating) reference frames. They're not "real" forces caused by interactions, but they're necessary to explain motion in these frames. Understanding these forces is crucial in analyzing rotating systems or motion on the Earth's surface.

32. How does the concept of force apply in relativistic physics?

In relativistic physics, force is defined as the rate of change of momentum, similar to classical physics. However, as objects approach the speed of light, their mass appears to increase, affecting how forces change their motion. This leads to modifications in how we apply and interpret forces at very high speeds.

33. What is the relationship between force and potential energy?

Force is related to potential energy through the concept of work. The work done by a conservative force is equal to the negative change in potential energy. Mathematically, F = -dU/dx, where F is the force, U is the potential energy, and x is position. This relationship is fundamental in understanding energy landscapes and force fields.

34. How do forces contribute to the formation and stability of chemical bonds?

Forces play a crucial role in chemical bonding. Electromagnetic forces between electrons and nuclei are responsible for covalent and ionic bonds. Van der Waals forces and hydrogen bonding, which are weaker intermolecular forces, also contribute to molecular interactions and material properties.

35. What is the concept of virtual work in relation to forces?

Virtual work is a principle used in mechanics where the work done by applied forces during a virtual displacement is equated to the work done by the constraint forces. This principle is powerful in analyzing equilibrium and dynamics of complex systems, especially when direct force analysis is difficult.

36. How do forces manifest in plasma physics?

In plasma physics, electromagnetic forces dominate. The motion of charged particles creates magnetic fields, which in turn affect the motion of other charged particles. This complex interplay leads to phenomena like plasma confinement in fusion reactors and explains many astrophysical observations.

37. What is the role of force in the theory of general relativity?

In general relativity, gravity is not seen as a force but as a consequence of the curvature of spacetime caused by mass and energy. What we perceive as gravitational force is actually the result of objects following geodesics (shortest paths) in curved spacetime.

38. How does the concept of force apply in statistical mechanics?

In statistical mechanics, forces are considered at the microscopic level to understand macroscopic properties. The collective effect of forces between particles determines thermodynamic properties like pressure and temperature. Statistical treatments of forces are crucial in explaining phenomena like phase transitions and material behavior.

39. What is the significance of the strong nuclear force?

The strong nuclear force is one of the fundamental forces of nature. It's responsible for binding quarks together to form hadrons like protons and neutrons, and for holding protons and neutrons together in atomic nuclei. It's the strongest of all fundamental forces but acts only over extremely short distances.

40. How do forces contribute to the phenomenon of resonance?

Resonance occurs when a system is driven at its natural frequency. Forces applied at this frequency, even if small, can lead to large amplitude oscillations. This phenomenon is important in various fields, from mechanical engineering (e.g., bridge design) to quantum physics (e.g., nuclear magnetic resonance).

41. How does the concept of force apply in cosmology?

In cosmology, forces play a fundamental role in shaping the universe. Gravity is the dominant force at cosmic scales, responsible for the formation of galaxies, stars, and large-scale structures. The balance between gravitational attraction and the mysterious repulsive force associated with dark energy determines the fate of the universe's expansion.

42. What is the relationship between force and pressure?

Pressure is defined as force per unit area. The relationship is expressed as P = F/A, where P is pressure, F is force, and A is the area over which the force is applied. This means that the same force applied over a smaller area will result in higher pressure.

43. What is torque and how is it related to force?

Torque is the rotational equivalent of linear force. It's a measure of the force that can cause an object to rotate about an axis. Torque is calculated as the product of the force and the perpendicular distance from the axis of rotation to the line of action of the force.

44. How does the concept of work relate to force?

Work is done when a force moves an object through a distance. It's calculated as the product of the force and the displacement in the direction of the force. If a force doesn't cause displacement, no work is done, even if effort is exerted.

45. What is the difference between mass and force?

Mass is a measure of the amount of matter in an object, while force is a push or pull acting on an object. Mass is a scalar quantity (it only has magnitude), while force is a vector quantity (it has both magnitude and direction). Mass is measured in kilograms (kg), while force is measured in Newtons (N).

46. What is the relationship between force and momentum?

Force is related to the rate of change of momentum. This relationship is expressed in Newton's Second Law as F = dp/dt, where F is the net force, p is momentum, and t is time. This form of the law is more fundamental than F = ma and applies in all reference frames.

47. How does the concept of impulse relate to force?

Impulse is the product of force and the time over which it acts. It represents the change in momentum of an object. The relationship is expressed as J = F⋅Δt = Δp, where J is impulse, F is the average force, Δt is the time interval, and Δp is the change in momentum.

48. What is the difference between weight and mass in space?

Mass remains constant regardless of location, even in space. Weight, however, changes with the strength of the gravitational field. In space, far from any significant gravitational source, an object would be weightless (experience no gravitational force) but still retain its mass.

49. What is the relationship between force and acceleration in circular motion?

In circular motion, the force causing the circular path (centripetal force) is related to acceleration by F = ma, where the acceleration a = v²/r, with v being the velocity and r the radius of the circular path. This means the centripetal force F = mv²/r.

50. How does the concept of force apply in fluid mechanics?

In fluid mechanics, forces play crucial roles in concepts like pressure, buoyancy, and drag. Pressure in a fluid exerts force on submerged objects, buoyant force opposes gravity, and drag forces resist motion through fluids. These forces are essential in understanding fluid behavior and object interactions in fluids.

51. What is the relationship between force and stress in materials?

Stress is the internal force per unit area within a material. When an external force is applied to a material, it creates internal stresses. The relationship is expressed as σ = F/A, where σ is stress, F is the applied force, and A is the cross-sectional area. Different types of stress (tensile, compressive, shear) result from different force applications.

52. What is the role of force in simple harmonic motion?

In simple harmonic motion, like that of a spring, the restoring force is proportional to the displacement from equilibrium and always acts towards the equilibrium position. This force is described by Hooke's Law: F = -kx, where k is the spring constant and x is the displacement.

53. What is the relationship between force and power?

Power is the rate at which work is done, or energy is transferred. Since work is the product of force and displacement, power can be expressed as P = F⋅v, where P is power, F is force, and v is velocity. This shows that power depends on both the magnitude of the force and how quickly it causes motion.

54. How do forces affect the behavior of fluids in motion?

Forces play a crucial role in fluid dynamics. They influence fluid flow patterns, pressure distributions, and phenomena like lift and drag. The interplay of forces like pressure, viscosity, and gravity determines fluid behavior in various situations, from blood flow in vessels to air flow around aircraft wings.

55. What is the role of force in the theory of elasticity?

In the theory of elasticity, forces are related to the deformation of materials. The relationship between force (or stress) and deformation (or strain) is described by Hooke's law for small deformations. Understanding these force-deformation relationships is crucial in materials science and structural engineering.