Difference Between Newton and Dyne – SI and CGS Units Explained
Force is a fundamental concept in physics, describing any interaction that causes an object to change its state of motion. The measurement of force plays a vital role in understanding motion, dynamics, and the effects objects exert on each other. To maintain consistency and clarity in scientific studies and practical applications, a standard unit is used to quantify force.
What is the SI Unit of Force?
The International System of Units (SI) is the globally accepted system for measuring all physical quantities, including force. In this system, the unit of force is called the newton, represented by the symbol N.
One newton is formally defined as the amount of force required to accelerate a mass of one kilogram at a rate of one metre per second squared.
Base Units Relevant to Force
To understand the unit of force, consider its three base quantities:
- Metre (m): unit of length
- Kilogram (kg): unit of mass
- Second (s): unit of time
Combining these, a newton can be broken down as:
- 1 N = 1 kg × 1 m/s²
Derivation of Newton as the SI Unit
Force is calculated using Newton’s second law of motion:
- F = m × a
- F = force (in newtons, N)
- m = mass (in kilograms, kg)
- a = acceleration (in m/s²)
This equation means that a force of one newton will accelerate a mass of 1 kilogram by 1 metre/second².
Common Units of Force and Their Conversions
| System | Unit Name | Symbol | Relation/Definition | Conversion |
|---|---|---|---|---|
| SI | Newton | N | Force to accelerate 1 kg by 1 m/s² | — |
| CGS | Dyne | dyn | Force to accelerate 1 g by 1 cm/s² | 1 N = 100,000 dyn |
| Imperial | Pound-force | lbf | Force to accelerate 1 lb by 32.174 ft/s² | 1 lbf ≈ 4.448 N |
SI Prefixes and Representation
The SI system supports the use of prefixes to express very large or small forces. For example:
- kN (kilonewton) = 1,000 N
- mN (millinewton) = 0.001 N
This use of prefixes makes it practical to write and interpret values across a wide range of applications.
Stepwise Approach to Force Calculations
- Identify the mass (m) of the object in kilograms (kg).
- Determine the acceleration (a) in metres per second squared (m/s²).
- Apply the formula: F = m × a.
- Express your answer in newtons (N) using SI units.
Worked Example
Suppose a force acts on a 2 kg object causing it to accelerate at 3 m/s². Calculate the force.
- m = 2 kg
- a = 3 m/s²
- F = m × a = 2 × 3 = 6 N
Therefore, a force of 6 newtons is applied to the object.
Summary Table: Force in SI System
| Physical Quantity | Base SI Unit | Symbol |
|---|---|---|
| Length | metre | m |
| Mass | kilogram | kg |
| Time | second | s |
| Force | newton | N (= kg·m/s²) |
Quick Reference: Key Formula
| Formula | Meaning |
|---|---|
| F = m × a | Force equals mass times acceleration |
| 1 N = 1 kg × 1 m/s² | Unit definition of newton |
Explore More on Vedantu
- What is Force?
- Newton’s Laws of Motion
- Force and Acceleration
- Force and Motion
- Work and Energy
- Contact and Non-Contact Forces
By understanding and using the SI unit of force—the newton (N)—students can accurately solve problems in mechanics and related areas. Practice identifying correct units in all calculations to build strong conceptual skills in physics.
FAQs on What is the Unit of Force in Physics?
1. What is the SI unit of force?
The SI unit of force is the Newton (N). It is defined as the force required to accelerate a mass of 1 kilogram by 1 meter per second squared (1 N = 1 kg × 1 m/s²). This standard is accepted internationally and is used in all Physics calculations based on the SI system.
2. What is the formula for force?
The formula for force is: F = m × a
- F = Force (in Newtons, N)
- m = Mass (in kilograms, kg)
- a = Acceleration (in meters per second squared, m/s²)
This equation follows Newton's Second Law of Motion.
3. What is the CGS unit of force and how does it differ from the SI unit?
The CGS unit of force is the Dyne (dyn). It is used in the centimeter-gram-second (CGS) system.
- 1 Dyne is the force required to accelerate 1 gram of mass by 1 centimeter per second squared (1 dyn = 1 g × 1 cm/s²).
- Conversion: 1 Newton (SI) = 100,000 Dyne (CGS)
4. How do you convert Newton (N) to Dyne (dyn)?
To convert Newton (N) to Dyne (dyn):
- 1 Newton (N) = 100,000 Dyne (dyn)
- Multiply the value in Newtons by 100,000 to get the equivalent in Dyne.
- Formula: Value in dyn = Value in N × 105
5. What are derived units of force?
Derived units of force are units obtained from the fundamental units of mass, length, and time. In the SI system, force is derived as:
- Newton (N) = kilogram meter per second squared (kg·m/s²)
- Dyne (dyn) = gram centimeter per second squared (g·cm/s²)
6. What is the difference between Newton and Dyne?
Newton (N) is the SI unit of force, while Dyne (dyn) is the CGS unit of force.
- 1 Newton = 100,000 Dyne
- Newton uses kilogram, meter, and second; Dyne uses gram, centimeter, and second
7. Why is Newton chosen as the SI unit of force?
Newton (N) is chosen as the SI unit of force because it is based on fundamental SI units (kilogram for mass, meter for distance, second for time) and is directly related to Newton’s Second Law of Motion: F = m × a.
8. What is the unit of force in the imperial system?
The unit of force in the imperial system is the pound-force (lbf).
- 1 pound-force (lbf) is the force needed to accelerate a 1-pound mass at a rate of 32.174 ft/s²
- 1 lbf ≈ 4.448 Newton (N)
9. Can you give examples of force units used in practical problems?
Yes, here are some common units used in Physics problems:
- Newton (N): Used in most Physics calculations (SI).
- Dyne (dyn): Used in older texts and CGS system problems.
- Pound-force (lbf): Used in engineering and the imperial system.
10. What are the common mistakes students make with force units?
Common mistakes include:
- Confusing force with weight; weight is a force but not all forces are weights.
- Mixing SI and CGS units without proper conversion (e.g., using kg and cm together).
- Neglecting to convert Newton to Dyne or vice versa when required.
11. How do you solve a numerical involving force unit conversion?
To solve a numerical involving force unit conversion:
- Write down the given value and its unit.
- Find the appropriate conversion factor (e.g., 1 N = 105 dyn).
- Multiply by the conversion factor to get the answer in the required unit.
Always check units at each step to avoid mistakes.
12. What is the dimensional formula of force?
The dimensional formula of force is [M L T-2].
- M = Mass
- L = Length
- T = Time
This helps in dimensional analysis and unit conversions.
