Discovery

Surface Tension

Greg Walker, NZSM

Have you every sat beside a pond and watched insects appear to walk on water. How do they do this?

See if you can lay a needle down onto the surface of a bowl of water. Why is this possible?

The answer is surface tension.

Water molecules are able to pull on each other with quite a strong force. Water molecules on the surface of the water are able to pull more strongly because there are no water molecules pulling on them from above. If an object resting on the water -- such as an insect -- is small and light, then the "pull" force of the water molecules stops it from sinking.

This is called surface tension. Surface tension is caused by the top layer of water molecules being pulled inward by the molecules underneath. This force is unbalanced, which results in the water in a container having a slight curve on its surface.

Square Bubbles?

Bend a piece of light wire in to a square. Make a soap bubble solution by mixing 250ml of water, 2 drops of dishwashing detergent and 3-4 drops of glycerine (get this at a supermarket or pharmacy).Dip your wire square into the soapy solution and try blowing some bubbles with it.

What shape are the bubbles that are made? Can you suggest why. Think about water molecules and surface tension. Try making some other shapes with the wire.

Floating Metal

Try floating a very thin piece of metal on the surface of a bowl of water. Old-fashioned double-edged razor blades are good for this.

Look at the blade from the side. What do you see? Now very gently touch one side of the metal. What happens? Why?

Flat Water

Take a cup and place it on a flat surface. Fill it right to the very top with water. Now take a straw and using it like a dropper add as many drops of water as you can to the cup without it spilling over.

Look from the side, at eye level, at the water surface of the cup. What do you notice?

Science on the Net

A range of sites covering topics from astronomy to earth science

http://www.nhm.ac.uk/
This site covers a range of interesting topics on biology, earth science and so on. The information is up-to-date with good graphics.

http://www.madlab.org/
Set up as part of the Edinburgh International Science Festival, Madlab is intended to introduce children to tasks related to practical electronics (soldering, for example). A range of project kits are provided with circuit diagrams and instructions for making a simple circuit board with flashing lights, to a robot that moves around a maze.

http://www.geocities.com/colosseum/Arena/7982/1.html
The author of this page has compiled a searchable list of biological resources from the web.

http://pages.prodigy.com/solarsystem/
This site is intended for teachers and others interested in astronomy. It covers planets, moons and rings, and is written for the layperson. It is advisable to start by looking at /aintro.htm which covers how to read the "book".

http://newproducts.jpl.nasa.gov/calendar/
This on-line calendar covers space-related activities and anniversaries for the coming year, plus links to related home pages.

http://www.quackwatch.com/
This is a very extensive collection of information about alternative medical treatments.

http://library.advanced.org/
The home page of ThinkQuest, an annual contest that challenges students, from 12 to 19, to "use the Internet to create Web based educational tools and materials that make learning fun and contagious".

Greg Walker, NZSM