Question

SI unit of force is :

• A. Joule
• B. Newton
• C. Pascal
• D. Watt

Hint:

Remember that force makes things move. Think of "Newton" as the man who saw the apple fall due to a "force" (gravity), so the unit is named after him. All other options like Joule and Watt are related to energy and its usage over time.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question identifies the standard International System of Units (SI) measurement for the physical quantity of "Force."
Step 2: Key Formula or Approach:
According to Newton's Second Law of Motion:
\[ \text{Force} (F) = \text{mass} (m) \times \text{acceleration} (a) \]
Step 3: Detailed Explanation:

Definition of the Newton: The SI unit of force is the Newton (N), named in honor of Sir Isaac Newton. It is a derived unit. By definition, one Newton is the amount of force required to accelerate a mass of one kilogram at a rate of one meter per second squared.

Dimensional Analysis: In terms of base SI units, \( 1 \text{ N} = 1 \text{ kg} \cdot \text{m/s}^2 \).

Analyzing Incorrect Units:
- Joule (A): This is the SI unit for energy, work, or heat. It represents force applied over a distance (\( 1 \text{ J} = 1 \text{ N} \cdot \text{m} \)).
- Pascal (C): This is the SI unit for pressure, defined as force per unit area (\( 1 \text{ Pa} = 1 \text{ N/m}^2 \)).
- Watt (D): This is the SI unit for power, defined as the rate of doing work or transferring energy (\( 1 \text{ W} = 1 \text{ J/s} \)).

Importance in Physics: Force is a vector quantity that causes an object to change its velocity (to accelerate). Correct units are fundamental for maintaining accuracy in all mechanical calculations.

Step 4: Final Answer:
The correct SI unit for measuring force is the Newton, derived from the product of mass and acceleration.

Answer 2

Another way to identify the SI unit of force is to think about which everyday quantity each of these units is actually used to report, since a unit's common usage reveals the physical quantity it belongs to.

1. Joule: This unit shows up when quantifying food energy (often paired with Calories) or the work a machine performs. It reports energy, which is a different quantity from force.
2. Newton: This unit shows up whenever a push or pull is being reported directly, for example, the thrust of a rocket engine or the weight of an object (weight itself is a force equal to mass times gravitational acceleration). Any place a push or pull is quantified numerically, Newton is the unit in use.
3. Pascal: This unit appears for tyre pressure, blood pressure, or atmospheric pressure, none of which is a force by itself, they are force spread over an area.
4. Watt: This unit appears on light bulbs, motors, and appliance labels to indicate how fast energy is being used or converted, which is a rate, not a push or pull.

Only one of these four units is the one actually used to report a push or pull directly.

Therefore, the correct answer is Newton.