Brownian motion from uneven air molecule collisions

Steps:

• Smoke particle Z is bombarded by surrounding air molecules in constant random motion.
• These molecules collide with Z from all directions due to thermal energy.
• Collisions are not perfectly balanced, creating a net unbalanced force.
• This imbalance causes Z to zigzag randomly, observed as erratic movement.

Why C is correct:

• Brownian motion is defined as the random displacement of particles from asymmetric collisions by smaller, faster-moving molecules in a fluid.

Why the others are wrong:

• A: Air molecules are actually much smaller than smoke particles, enabling frequent collisions.
• B: While air molecules are smaller, size difference alone doesn't explain the random directionality of hits.
• D: Air molecules translate freely in gas, not vibrate in fixed positions like in solids.

Final answer: C