If SI unit of mass is Kg, what is the SI unit of weight?
Newton
Weight: Understanding its SI Unit
The question asks about the SI unit of weight, given that the SI unit of mass is the kilogram (Kg). To answer this, it's important to understand the fundamental difference between mass and weight.
Mass is a fundamental property of matter that measures the amount of substance in an object. It is a scalar quantity, meaning it only has magnitude and no direction. The SI unit of mass is indeed the kilogram (Kg).
Weight, on the other hand, is a measure of the gravitational force exerted on an object. It is a vector quantity, possessing both magnitude and direction (always pointing towards the center of the gravitational body, e.g., Earth). Since weight is a force, its SI unit is the same as the SI unit for any other force.
The relationship between weight, mass, and acceleration due to gravity is given by the formula:
$$ W = mg $$
Where:
- \( W \) is weight
- \( m \) is mass (in kilograms, Kg)
- \( g \) is the acceleration due to gravity (approximately \( 9.8 \, m/s^2 \) on Earth)
According to Newton's second law of motion, force (F) is equal to mass (m) multiplied by acceleration (a):
$$ F = ma $$
The SI unit of mass is kilogram (Kg) and the SI unit of acceleration is meters per second squared (\( m/s^2 \)). Therefore, the SI unit of force is \( Kg \cdot m/s^2 \). This combined unit is defined as the Newton (N).
Thus, since weight is a form of force, its SI unit is the Newton.
Mass vs. Weight: Key Differences
Understanding the distinction between mass and weight is crucial in physics. Here's a brief comparison:
| Feature | Mass | Weight |
|---|---|---|
| Definition | Amount of matter in an object. | Gravitational force acting on an object. |
| Nature | Scalar quantity (magnitude only). | Vector quantity (magnitude and direction). |
| SI Unit | Kilogram (Kg). | Newton (N). |
| Measurement | Measured using a beam balance. | Measured using a spring balance. |
| Variation | Constant everywhere in the universe. | Varies with gravity (e.g., different on Moon vs. Earth). |
Analyzing the Options for Weight's SI Unit
Let's evaluate the given options based on our understanding of weight and its SI unit:
- kg/s2: This unit represents mass divided by the square of time, which does not correspond to force or weight. It's dimensionally incorrect for weight.
- kg: This is the SI unit of mass, not weight. Mass and weight are distinct physical quantities.
- kg m/s: This unit is the SI unit for momentum (\( p = mv \)), where \( m \) is mass and \( v \) is velocity. It is not the unit for force or weight.
- Newton: As explained, Newton is the SI unit of force, defined as \( Kg \cdot m/s^2 \). Since weight is a force caused by gravity, Newton is indeed its correct SI unit.
Therefore, the SI unit of weight is the Newton.
Important Questions from Units and Dimensional Formula
Parsec is a unit of ______.
'Torr' is a unit of _______.
Electron-volt is a unit of ______.
Which of the following is the SI unit for measuring the amount of a substance?
Weber per second is equivalent to ______.
