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Ch 18: Thermal Properties of Matter
Young & Freedman Calc - University Physics 15th Edition
Young & Freedman Calc15th EditionUniversity PhysicsISBN: 9780135159552Not the one you use?Change textbook
Chapter 18, Problem 34a

Smoke particles in the air typically have masses of the order of 101610^{-16} kg. The Brownian motion (rapid, irregular movement) of these particles, resulting from collisions with air molecules, can be observed with a microscope. Find the root-mean-square speed of Brownian motion for a particle with a mass of 3.00×10163.00\(\times\)10^{-16} kg in air at 300300 K.

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1
Start by understanding the concept of root-mean-square speed, which is a measure of the average speed of particles in a gas. It is derived from the kinetic theory of gases.
Use the formula for root-mean-square speed: 3kTm, where k is the Boltzmann constant (1.38×10-23J·K-1), T is the temperature in Kelvin, and m is the mass of the particle.
Substitute the given values into the formula: 3×1.38×10-23·3003.00×10-16.
Calculate the numerator: 3×1.38×10-23·300, which represents the product of three constants and the temperature.
Calculate the root-mean-square speed by taking the square root of the fraction obtained from the previous steps, which involves dividing the calculated numerator by the mass of the particle.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Brownian Motion

Brownian motion refers to the random movement of particles suspended in a fluid, resulting from collisions with fast-moving molecules in the fluid. This phenomenon is crucial for understanding the behavior of smoke particles in air, as it explains their rapid and irregular motion observed under a microscope.
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Root-Mean-Square Speed

The root-mean-square speed is a measure of the average speed of particles in a gas, derived from the kinetic theory of gases. It is calculated using the formula v_rms = sqrt((3kT)/m), where k is the Boltzmann constant, T is the temperature, and m is the mass of the particle. This concept helps quantify the speed of Brownian motion for smoke particles.
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Kinetic Theory of Gases

The kinetic theory of gases explains the macroscopic properties of gases by considering their molecular composition and motion. It provides the basis for calculating the root-mean-square speed, as it relates temperature and particle mass to the average kinetic energy, essential for understanding the dynamics of particles like those in Brownian motion.
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Introduction to Kinetic-Molecular Theory