Question

What is the SI unit of Force?
(a). Torr
(b). Newton
(c). Joule
(d). Dyne

Answer 1

Hint: Convert the mathematical formula of Pressure into basic units in the MKS system.
The correct option is B, i.e., Newton.

Complete step-by-step solution -

The International System of Units (SI) is the modern form of the metric system. It is the only system of measurement with official status in nearly every country in the world. It comprises a coherent system of units of measurement starting with seven base units.
Second (the unit of time with the symbol s),
Meter (length, m),
Kilogram (mass, kg),
Ampere (electric current, A),
Kelvin (thermodynamic temperature, K),
Mole (amount of substance, mol)
Candela (luminous intensity, cd)

Force is any interaction that, when unopposed, will change the motion of an object. A force can cause an object with mass to change its velocity (which includes beginning moving from a state of rest), i.e., to accelerate. Force can also be described intuitively as a push or a pull.
Mathematically it can be described as
$$F=\quad mass\quad \times \quad acceleration$$
We will now convert the above formula into basic units, as discussed above in the section of SI units. Mass is measured in kilograms, and units of acceleration are meters per second square.
$$ F=\quad kilogram\quad \times \quad \dfrac { meter }{ { (second) }^{ 2 } }$$
$$ SI\quad unit\quad of\quad Force,\quad F=\dfrac { kg.m }{ { s }^{ 2 } }$$
This quantity is termed as one Newton (N).
So the Newton is the SI unit of Force. It strictly defined: the Force that will give a mass of 1 kilogram an acceleration of 1 meter per second squared.
In the metric system, the Force is measured in kilograms. When we talk about the CGS unit of Force, it is measured in dynes.
Additional Information:
Some of the commonly used units of Force are:
Dyne (dyn) = 10-5 N
Gram-force (gf) = 9.8 mili-Newton
Kilogram-force (KgF) = 9.8 Newton
Poundal (Pdl) = 138.3 mili-Newton

Note: Students usually get confused between Newton and Joule. Joule is the SI unit of energy, whereas Newton is the SI unit of force.