Mr. Brown's Motion
You’ve probably seen a sunbeam streaming through a window like the windows in this church. What you’re actually seeing is sunlight reflected from tiny dust particles in the air.
The Back Story
- Did you ever look closely at the dust particles in a beam of sunlight? If you did, you may have noticed that the dust particles were constantly moving in the air. Any tiny particles suspended in a fluid move about randomly, like dust particles in the air.
- This motion was first discovered by a British scientist named Robert Brown in 1827. That’s why this type of motion is called Brownian motion. Brown observed tiny pollen grains moving randomly in water.
- What causes Brownian motion? Watch this animation and see if you can figure it out. http://www.aip.org/history/einstein/brownian.htm
Can You Apply It?
Learn more about Brownian motion at the links below. Then answer the questions that follow.
- Describe Brownian motion.
- Brownian motion occurs in mixtures. What type of mixtures exhibit Brownian motion?
- Why does Brownian motion occur?
- What size of particles move by Brownian motion? Why do particles of this size exhibit Brownian motion?
- What factors affect the speed of Brownian motion? How do the factors affect the speed?
- What is the kinetic theory of matter? How does it explain Brownian motion?
- Based on what you now know about Brownian motion, predict what would happen if you placed a drop of food coloring in a large pan of water. Assume that you do not stir or disturb the water in any way. Explain your prediction.