Walk On Water ??? Really ???
Posted by Art Gatenby on Thu, Sep 10, 2009 @ 03:31 PM
Yes you can walk on water with Surface Tension.
I am frequently asked about surface tension : what it is all about, why it’s important, what it does and how it applies to different substances.
I find that definitions of surface tension range from the simple:
Surface tension refers to water’s ability to “stick to itself”.
to the more technical:
A liquid exists as a liquid because of the attractive forces between molecules. These are called intermolecular forces or van deel Waals’ forces.
Molecules within the liquid are surrounded by other molecules and are attracted in every direction with equal force. Molecules exposed to the surface are unstable because of the attractive forces are not equal and they are drawn away from the surface. As a result the liquid tends to contract the surface area until the equilibrium is reached.
That happens when the surface reaches its minimum.
These intermolecular forces which contract the surface are called “Surface Tension”.
Now about water walking.
Many bugs do it. Here is a picture of a happy Wasp and a struggling Wasp. As the temperature of water increases surface tension goes down — the force between molecules becomes less. The bug will begin to sink like the wasp on the right.
Like the bug a paper clip will float given the right surface tension. If the temperature starts to go up like the Wasp, the paper clip will begin to sink.
Consider the opposite. Surface tension increases as temperarure goes down. A lower temperature creates more force holding the molecules together. When it becomes ice you can walk on it even skate on it.
Aside from a few bugs and ice skaters who cares about surface tension?
Soap and detergent manufacturers do. Their products lower surface tension so that dirt can be washed out.
Ink, paint and coatings producers are very sensitive to surface tension because it determines how their product reacts with the paper, or a wall or a plastic bag.
The form of your medicine has a lot to do with the control of surface tension. It is a factor in production of liquid drugs and in many pills.
The measurement of surface tension can also define the cleanliness of water. It can be a measure of trace impurities. These users are a sample of who else cares about surface tension.
We make instruments that do these measurements. They are called Tensiometers.
In future musing or rants I’ll describe some of the techniques used to measure surface tension.
I hope this has been useful and entertaining.
Let me know if there are any test equipment issues you would like to hear about
Art