Why does smoke appear to move when you look at it under a microscope?

Because its a gas and its always changing forms. hope this helped

Smoke particles are larger than air particles That's why we can see the smoke particles better than the air particles, gas particles always move at high speed, in random directions.The same things is happening to air particles When air particles collide with smoke particles, the smoke particle moves  the same direction as the air particle that hit it. When another air particle hits the smoke particle, it changes its direction to the second air particle, and so on. This is called Brownian motion