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A measure of the tendency to flow is viscosity. Viscosity is a concept that is roughly equivalent to the term "thickness". Water flows readily because it is thin (or less viscous), syrup flows more slowly because it is thicker then water (or more viscous) and tar is even slower because it is very viscous. Basically a high viscosity means that it flows (or pours) slowly.

Background Information

The Particle Theory

According to the particle theory, all matter is composed of smaller particles which are always moving (See lesson 1 for a review of the particle theory). These particles have attractions for each other. It is the attractions between molecules that causes viscosity.

Strong attraction = high viscosity	less attraction = less viscous	low attraction = low viscosity

This force or attraction is called friction. When a fluid pours, the force of gravity pulls down but the force of friction works against gravity. The forces of friction between the particles in some fluids are stronger then in other fluids. If the force of attraction is very strong, the liquid will pour slowly compare to a liquid with weaker intermolecular attraction.

Activity

Experiment Time:

Aim: To study the viscosity of liquids

Materials:

-molasses
-water
-two clear measuring cups (or one and wash it in-between the experiments)
-two bowls
-watch or clock with a second hand

Method:

1. Measure exactly 125 ml (or 1/2 cup) of molasses into a clear measuring cup.

2. Slowly pour the molasses into the bowl. Record the time required to pour the molasses.

3. Measure exactly 125 ml (or 1/2 cup) of water into a clear measuring cup.

4. Slowly pour the molasses into the bowl. Record the time required to pour the water.

Observations:

Prepare a table to record your results.

Exercise 2.4

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