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What is the SI unit of pressure?

$N \cdot m$

$N$

$N \cdot m^{-1}$

$N \cdot m^{-2}$

Correct Answer

🔬 SC • Science Concept & PrincipleGeneral SciencePrevious Year Paper 2024

Option D

$N \cdot m^{-2}$

Quick Summary:

Pressure is defined as the physical force exerted on an object per unit area of the surface in contact. Since the SI unit of force is the Newton ( $\text{N}$ ) and the SI unit of area is the square meter ( $\text{m}^2$ ), the SI unit of pressure is the Newton per square meter ( $\text{N m}^{-2}$ ), which is also known as the Pascal ( $\text{Pa}$ ).

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🔬SCScience SolutionConcept & Principle

💡 Explanation

💡 Everyday Analogy (Real-World Intuition)

Think of a sharp knife versus a blunt one: the sharp knife has a much smaller edge area, so the force of your hand produces high pressure, making it easy to slice through vegetables.

🧠 Memory Mnemonic / Shortcut Aid

P = F / A (Pressure = Force / Area) — 'P is the Force over the Area'.

🔢 Key Formulas

$P = \frac{F}{A}$ — Where $P$ is pressure, $F$ is normal force in Newtons, and $A$ is area in square meters.

$1 \text{ Pa} = 1 \text{ N m}^{-2}$ — The definition relating Pascal to the base SI unit combination.

⚙️ Working Principle

The principle of pressure states that $P = \frac{F}{A}$ , where $P$ is pressure, $F$ is the normal force, and $A$ is the contact area. If the same amount of force is applied to a smaller area, the pressure exerted increases significantly because the distribution of force is concentrated.

📌 Key Points

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Pressure is a scalar quantity.
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The Pascal ( $\text{Pa}$ ) is the derived SI unit of pressure.
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Atmospheric pressure is often measured in bar or hectopascals ( $\text{hPa}$ ).

🛠️ Applications / Uses

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Hydraulic braking systems in vehicles.
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Determining the bearing capacity of soil for building foundations.

📄 Additional Information

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Standard atmospheric pressure at sea level is approximately $101,325 \text{ Pa}$ or $101.3 \text{ kPa}$ .
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Option A ( $\text{N m}$ ) is a unit of torque (Newton-meter).
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Option B ( $\text{N}$ ) is the SI unit of force.
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Option C ( $\text{N m}^{-1}$ ) is the unit for spring constant or surface tension.

📊 Diagram / Illustration

✅

D is correct — The SI unit of pressure is the Newton per square meter ( $\text{N m}^{-2}$ ), which is equivalent to the Pascal ( $\text{Pa}$ ).

Core Concepts Used

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Pressure SI Units Force and Area

💡 EXAM TIP

Always remember the difference between force ( $\text{N}$ ), energy/work ( $\text{N m}$ or Joules), and pressure ( $\text{N m}^{-2}$ or Pascals) to avoid confusion in exam questions.

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