SurfaceTension

Have you ever seen insects skate or walk on water? if not watch the video below.

So how do the insects stay on top of the water. They are not floating they actually standing on a skin of the water that is called surface tension. It is surface tension that holds drops together when they fall as rain, they may splash when they hit the ground because the surface tension can not hold the water molecules together as they all go in different directions.

Surface tension is not amazingly strong, an animal bigger than the pond-skaters (who have big feet) would break through the surface tension.

A pin made of steel is too dense to float, throw one into a basin and see what happens.

Now place one on a piece of paper and lay it on the top of a bowl of water.... what happens,

you can also lower it onto the surface using a fork.

To demonstrate the breaking of Surface tension,

Get a piece of thin plastic, not too thin (similar to a credit card) but that will float on the water. Cut it or score it in to the shape of the image below

Place the ST boat in the middle of the basin/bath, add a drop or two of washing up detergent, observe.

What happened? Why?

Capillary tubes

Capillary action is due to surface tension, the tension has the ability to pull water up narrow glass tubes, but also up the tiny tube structures in kitchen paper, and other 'wicks'. Plants use this to draw water up their stems. This is how plants get water to the photosythesis sites (leaves) as water is needed for photosynthesis to occur.

To help you witness this, cut out a 5 pointed star from coloured paper. Fold the fingers of each point back onto the body of the star, score along the join, when completed place in water and observe!

Well what did you see?

Bubble mix

glycerine : water : washing-up liquid

1 : 4 : 2

Investigate the effect of heating on Surface tension