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A physics problem solved

December 24, 2013

By Barry Tucker

I’ve solved a common household problem: how to remove tiny floating objects from liquids.

You have probably noticed that if you take a spoon, manoeuvre the object to the side of the cup or bowl and try to lift it out with the “pointy” end of the spoon, the liquid will flow to the outside edge of the spoon and the floating object will go with it. It’s frustrating.

The object floats on the surface because it’s not heavy enough to sink. As the liquid flows one way or the other, the floating object moves in the same direction — over the edge of the spoon.

The simple solution is to use the same tendency of the liquid to move to float the object onto the spoon. This is best done in the centre of the cup or bowl rather than at the edge.

Drag the object to the centre, tilt the spoon alongside the object and it will float onto the spoon. Allow only a small amount of liquid to flow with the object. Last step: lift it out!

Here’s another tip. This one avoids spilling liquid over the edge of your cup while stirring.

When you stir your coffee, say, around and around in a continuous circular motion you create what I call a centrifugal force “wave”. Centrifugal force causes any movable object or liquid to move away from the centre. If it encounters something immovable (the side of your cup) it is then forced upwards. Eventually the liquid you are stirring will spill over the side of your cup.

To avoid this overflow, stir the liquid back and forth around the left- or right-hand side of the cup. This avoids creating the centrifugal force wave. Of course, if you stir vigorously enough you will still create spillage.

I look forward to receipt of my Nobel Prize for Physics! Just stirring, of course.


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