Problem 16 - An Introduction to Physical Science

Question

Choose the word or phrase that best answers the question. Which is a unit of pressure? A) \(\mathrm{N}\) B) \(\mathrm{kg}\) C) \(\mathrm{g} / \mathrm{cm}^{3}\) D) \(\mathrm{N} / \mathrm{m}^{2}\)

Step-by-Step Solution

Answer

Option D (\text{N/m}^{2}) is a unit of pressure.

Step 1: Understanding Units of Measurement

First, identify what pressure is and what its units are. Pressure is defined as force per unit area.

Step 2: Analyzing the Options

Review each option to determine if it matches the definition of pressure (force per unit area):- Option A: \(\text{N}\) stands for Newton, a unit of force.- Option B: \(\text{kg}\) stands for kilogram, a unit of mass.- Option C: \(\text{g/cm}^{3}\) stands for grams per cubic centimeter, a unit of density.- Option D: \(\text{N/m}^{2}\) stands for Newton per square meter, which can be simplified to the pascal (Pa), the SI unit of pressure.

Step 3: Selecting the Correct Answer

Since pressure is defined as force per unit area and \(\text{N/m}^{2}\) fits this definition, Option D is the correct answer.

Key Concepts

Pressure Measurement

Pressure is a fundamental concept in physics and engineering.
It is defined as the force exerted per unit area.
Essentially, it measures how much force is applied over a specific surface area.
To better understand this, imagine pressing your hand on a table.
The harder you press, the more force you apply over the area of your hand.
In scientific terms, pressure (\text{P}) is calculated as force (\text{F}) divided by area (\text{A}):
\( P = \frac{F}{A} \)
There are various units used to measure pressure, depending on the context, such as atmospheres (atm), bars, and millimeters of mercury (mmHg).
However, the most commonly used and internationally recognized unit is the pascal (Pa).

SI Units

The International System of Units (SI) is the standard metric system used globally for scientific and industrial measurements.
It establishes a universal framework that ensures clarity and consistency.
Within this system, the pascal (Pa) is the designated unit of pressure. One pascal is defined as one newton per square meter (N/m²).
This choice simplifies the relationship between the units of force and area, making calculations straightforward.
Here's how the other units relate to pressure in comparison:

• Newton (N): A unit of force, not pressure.
• Kilogram (kg): A unit of mass, not related to pressure.
• Grams per cubic centimeter (g/cm³): A unit of density, not pressure.

Therefore, the stringent use of SI units aids in minimizing errors and misunderstandings in scientific communication.

Force Per Unit Area

Pressure as 'force per unit area' is a concise way to understand how forces act over surfaces.
For a practical example, consider a knife: the force applied through the handle is concentrated at the thin edge of the blade.
This high force over a small area generates a high pressure, able to cut through materials.
Similarly, when pressure is to be calculated, distributing the force over a specified area is essential.
Let's revisit the formula: \( P = \frac{F}{A} \)
Pressure is higher when a large force is concentrated over a small area (and vice versa). This principle is widely applied in various engineering fields, like hydraulics and pneumatics.
Recognizing this relationship helps in designing systems where controlling pressure is critical, ensuring safety and efficiency.