::: altering surface tension – experiment
Have you ever tried to float a paper clip in a glass of water? Well we’re here to tell you it doesn’t work unless of course you know how to alter the surface tension of the water that is, and luckily for you, we do!
Take a glass of water and a piece of cheap tissue or paper towel.
Tear up a piece of tissue, a little bigger than the paper clip but small enough to fit inside the glass. Lay the piece of tissue on the surface of the water.
Once it is completely wet gently place the paper clip on top of the tissue.
Now using a skewer or some other thin implement very gently push the tissue away from the paper clip to the bottom of the glass.
Try not to touch the paper clip or you may break the surface tension.
Your paper clip should now be floating on top of the surface.
If you look closely you can see how the surface tension has altered. It looks a bit like a skin has formed on top of the water but actually the water has depressed beneath the paper clip and raised slightly inside and around the paper clip, just like as happens when a water strider insect walks on water.
Our second experiment at altering the surface tension is demonstrated in the video below. For this experiment we used the chocolate shaker we use for our morning cappuccinos (as you do!) as it requires a mesh type lid.
Fill up the container with water and place a piece of regular cardboard on top, and tip it upside down. Just be sure to hold it really flat.
Carefully slide the cardboard away … and presto.
The reaction of the card being dragged across the surface effects the surface tension, creating a kind of skin between the mesh holes which holds the water in.
Tip it ever so slightly to break the surface tension and the water escapes!
Here watch this video, it explains it all much better than we can!
Another surface tension experiment is where you use full cream milk, food colouring and detergent. Place some milk into a flat dish. You don’t need much. Our dish was about 1cm (1/2 ” deep) . Next place a few dots of food colouring near the center of the milk.
We used a straw for the next bit but you could use a pipette or an eye dropper. Place one drop of detergent into the center of the colour and watch how the detergent breaks the surface tension … Woohoo!
We know there are other experiments on altering the surface tension out there. One that comes to mind has to do with pepper to propel boats or something like that. If you can help us out with that one or any others please do!
In a shallow tub of water, place a bread bag clip (your boat) then put a drop of detergent in the whole part of the bread clip and the boat will zoom across the water.
::: So cool … Thanks Linda, you’re a little ripper!!!
The boat one involves a making a boat out of card that has a point at the front and a triangle cut out of the bottom (the triangle has to be point at the back not the front). You place the boat gently on the water and then place a drop of detergent in the triangle hole which moves the boat across the water as the detergent spreads across the surface of the water. Not to get too scientific but I explain it to my Preps as the detergent is made up of tiny particles and these particles are fat and bullies and they push the water particles out of the triangle thus propelling the boat forward.
(similar to this http://www.youtube.com/watch?v=UHqGS0NE0T8)
The pepper one (I call it scared pepper) is to sprinkle pepper over a bowl of water and place a drop of detergent in the middle and the pepper will disperse quickly across the top of the water. Same kind of science behind this as the detergent pushes the pepper across the top of the water.
(like this http://www.youtube.com/watch?v=fHsd0pThp88)
Both experiments can be repeated until either your boat is soggy or the water has too much detergent in it.
Hope that helps
::: Yes …yes … YES! It’s all coming back to me know … Thanks for filling in the gaps Mrs. Allaki!
Oh oh just remembered another one from my uni days were you can fill a glass of water up and gently add coins to the glass until the water level rises up and you can see the meniscus before the water overflows. This is a good way to show how the water holds together like a skin.
::: That’s another really good example Mrs. Allaki … Thanks again!
Fantastic! love it lots of things to fascinate the boys…by the way have you tried here for your pepper and boat tricks… http://www.kids-science-experiments.com/speedboatmatchsticks.html …looks like fun!
::: Thanks for the heads-up on the science site Findleysmaid!
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