Physics

Gilla:		Dela:

Video

Materials

• 2 drinking glasses
• Food coloring
• Water

Short explanation

Water molecules move all the time - and they move more the hotter the water is. The more they move, the faster the food coloring spreads among them.

Long explanation

Temperature is a measure of how much the particles in a chemical substance move. The higher the temperature of a chemical substance, the more the particles in it move. If a chemical substance consists of solitary atoms, as, for example, a noble gas does, the atoms move up-down, right-left and forward-backward (translational movement), but they also rotate and vibrate. If a chemical substance consists of many atoms composed of larger molecules or ionic compounds, most of the movement is only vibrations. However, water molecules are quite small so they move both translationally, rotate and vibrate.

The fact that particles constantly move means they collide with each other. Therefore, if you look at an individual particle, it looks like it's moving randomly here and there. This random movement of particles causes a substance to move from high to low concentration over time - thus spreading evenly. This process of even distribution is called diffusion.

When the food color is added, each color molecule will be pushed around by the surrounding water molecules. If you would only look at one color molecule it would move randomly about. This phenomenon is called Brownian motion, after the botanist Robert Brown. He saw this happening to pollen grains in water. Albert Einstein later studied the phenomenon and made it a strong argument for the existence of atoms and molecules.

A single water molecule can also be said to undergo Brownian motion, although it's hard (or impossible?) to observe a single water molecule among all the others.

Diffusion can be thought of as a macroscopic manifestation of Brownian motion.

In this demonstration, you will see how the food color and the water mix. This happens by diffusion. Both the water and the color diffuse. The difference between the glasses is the temperature of the water. The higher the temperature of a substance, the faster the particles in it move and the faster diffusion goes.

Experiment

You can turn this demonstration into an experiment. This will make it a better science project. To do that, try answering one of the following questions. The answer to the question will be your hypothesis. Then test the hypothesis by doing the experiment.

• What happens if you use milk instead of food coloring?
• What happens if you use cooking oil instead of food coloring?
• What happens if you use sugar instead of food coloring?
• What happens if you increase the temperature difference between the glasses?
• What happens if you use less food coloring?
• What happens if you use two food colors in each glass?
• What happens if you pour in larger particles, such as sesame seeds?

Gilla:		Dela: