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Abstract

This science fair project was conducted to observe how adding salt to water and increasing its temperature can affect the surface tension of water. The experiment was done by adding grains of rice to a piece of aluminum foil floating on water of varying temperatures, i.e. of 15C, 25C, 35C, 45C and 55C.

Hypothesis

When salt is added to water and the temperature of the water increased, the surface tension of water is reduced.
 

Scientific Terms

Surface tension, interface tension, Van der Waal forces, gravity

Background

Surface tension of water

Surface tension in water describes a condition where the surface of water that is in contact with air acts like a thin elastic sheet. It is a phenomenon that occurs on the surface of liquids when they are in contact with a gaseous medium. When there is contact between the surfaces of two liquids like water and oil, it is called interface tension.

The molecules in a liquid (eg. water) are drawn together by intermolecular forces known as Van der Waal forces. The molecules on the surface of the water are not surrounded by water molecules on all sides.  They will cohere more strongly with neighboring water molecules, as opposed to air molecules. This creates a “film” on the surface which requires a certain amount of force to penetrate.

The shape that is formed by a drop of water is caused by surface tension. Ideally all liquids will form a spherical shape in the absence of gravity in order to minimize their surface tension. This is because the sphere has the smallest surface area for a given volume. However, the shape of a water droplet is not spherical due to the force of gravity.
 

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Complexity level:
5
Project cost ($):
10
Time required:
1 hour to prepare, 4 hours for observation
Material availability:
Easily found
Safety concerns:

None