Video: Describing Particles Moving with Brownian Motion

Which of the following statements could describe particles moving with Brownian motion? [A] Vibrating particles suspended in a liquid. [B] Randomly moving particles suspended in a liquid or gas. [C] Randomly moving particles suspended in a solid. [D] Vibrating particles suspended in a liquid or gas. [E] Vibrating particles suspended in a solid.

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Video Transcript

Which of the following statements could describe particles moving with Brownian motion? (A) Vibrating particles suspended in a liquid. (B) Randomly moving particles suspended in a liquid or gas. (C) Randomly moving particles suspended in a solid. (D) Vibrating particles suspended in a liquid or gas. Or (E) vibrating particles suspended in a solid.

Brownian motion is the chaotic or random way a particle moves due to collisions with particles of a liquid or gas. Every time a particle hits another particle, it loses or gains some energy and changes direction and speed. When we model particles and try and understand Brownian motion, we usually have to make them ideal hard spheres because it’s too complicated to do the math if we take their full shape into account. We also assume that there are no internal bonds. We assume just one lump which isn’t vibrating and isn’t rotating.

Since Brownian motion deals with the movement of particles and not vibrations, we can eliminate the options that mention vibrating particles. Option (C) says that we could describe particles moving with Brownian motion as randomly moving particles suspended in a solid. However, Brownian motion only occurs in a fluid, a liquid or a gas. And in solids, particles vibrate on the spot and don’t move overall. So our final answer is that particles moving with Brownian motion are randomly moving particles suspended in a liquid or gas, although you can refer to this as chaotic.

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