Newton (unit)
SI unit of force, named after Isaac Newton.
The newton (symbol: N) is the SI unit of force. It’s a derived unit, meaning it’s built from the base units of the International System: one newton equals one kilogram metre per second squared (1 kg⋅m/s²). In practical terms, that’s the amount of force required to make a one-kilogram object speed up by one metre per second every second.
The unit gets its name from Isaac Newton, thanks to his second law of motion. That law says force equals mass times acceleration (F = ma). When you plug in kilograms for mass, metres for distance, and seconds for time, you get the newton.
The definition was set in 1946 by the General Conference on Weights and Measures (CGPM), which standardized the MKS (metre–kilogram–second) unit of force as the force needed to accelerate one kilogram at one metre per second squared. Two years later, in 1948, the 9th CGPM gave that force the name “newton.” The MKS system later evolved into the modern SI, making the newton the official SI unit of force.
Because the unit is named after a person, its symbol is capitalised (N), but the full name is written in lowercase except at the start of a sentence or in titles.
On Earth, where standard gravity is about 9.80665 m/s², a one-kilogram mass presses down with roughly 9.81 newtons of force (its weight). An average apple (200 grams) exerts about two newtons. An average adult (62 kg) exerts about 608 newtons.
For larger forces, kilonewtons (kN) are used: 1 kN = 1000 N. For instance, a Class Y steam locomotive’s pulling power and an F100 jet engine’s thrust each come to around 130 kN. Climbing ropes are tested to withstand a fall generating 12 kN of force, and must survive five such tests without breaking.
- symbol
- N
- defined_as
- 1 kg⋅m/s²
- system
- International System of Units (SI)
- named_after
- Isaac Newton
- based_on
- Newton's second law of motion (F = ma)
Lore & Background
The MKS system later became the blueprint for today's SI system of units, making the newton the standard unit of force in the International System of Units. The unit is named after Isaac Newton, connecting to his second law of motion, which states that the force exerted on an object is directly proportional to the acceleration it acquires: F = ma. When using SI units of mass (kg), distance (m), and time (s), this law yields the definition of the newton as 1 kg⋅m/s². As with every SI unit named after a person, its symbol starts with an upper case letter (N), but when written in full, it follows the rules for capitalisation of a common noun—'newton' becomes capitalised only at the beginning of a sentence or in titles.
Reader's Guide
The newton is the fundamental unit of force in the SI system, directly derived from Newton's second law of motion. Its definition—1 kg⋅m/s²—provides a clear, measurable standard for force in scientific and engineering contexts. Climbing ropes are tested to withstand falls generating 12 kN of force. The newton's connection to Isaac Newton's second law ensures its theoretical foundation remains tied to classical mechanics, while its adoption by the CGPM made it an international standard. Its consistent definition across all SI base units allows precise calculation and comparison of forces worldwide.
Did You Know?
- A newton is defined as 1 kg⋅m/s², the force needed to accelerate one kilogram at one metre per second squared.
- Climbing ropes are tested to withstand falls that create 12 kN of force, and must not break after five such tests.
Frequently Asked Questions
What is the newton (N)?
The newton is the SI unit used to measure force. It represents the amount of force needed to accelerate a one-kilogram mass at one metre per second squared.
How is one newton defined mathematically?
One newton equals 1 kg⋅m/s², which is a direct expression of Newton's second law (F = ma). In other words, it ties force to the product of mass and acceleration.
Who is the newton named after and why?
The unit honours Sir Isaac Newton, whose second law of motion provides the exact relationship the unit quantifies. His work on classical mechanics gave scientists a practical way to express force numerically.
How much force is one newton in everyday terms?
One newton is roughly the weight of a small apple sitting on a kitchen counter. It is a modest, human-scale force—far smaller than the kilonewtons that support a parked car, yet larger than the millinewtons a fingertip exerts on a key.
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