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When a solid object is suspended in a beaker filled with water placed on a weighing machine, the reading increases and but the object is suspended in a beaker filled with air, the reading does not increase. What is the reason behind this.

MrAP
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  • See the above duplicate.Yes it does increase the weight shown on the sales. – John Rennie Sep 13 '16 at 10:48
  • I have edited my question. Please have a look. – MrAP Sep 13 '16 at 11:29
  • You might want to draw your setup. – Jan Bos Sep 13 '16 at 11:36
  • Both the beaker-with-water and beaker-with-air systems are subject to Archimedes' forces from the surrounding atmosphere. In the latter case the solid object (in order to be suspended and not float up or down) must be exactly as dense as air, so replacing part of the air in the beaker with a solid object changes nothing. It's a different matter if the beaker is in vacuum and/or filled to the brim with air/water before adding an object. – LLlAMnYP Sep 13 '16 at 11:55
  • In fact, if you have a beaker filled with water to the brim and then add an object that is lighter than water, the reading will very slightly decrease as some water is displaced, but the upwards Archimedes' force of the atmosphere very slightly increases. If this is in a vacuum and the beaker is filled with a gas, then nothing changes. If the beaker is only, say, half full with a gas (or with water), the reading increases. – LLlAMnYP Sep 13 '16 at 11:57
  • @JohnRennie: the duplicate mentioned is not a duplicate. – kpv Sep 13 '16 at 12:42

1 Answers1

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First of all, the duplicate mentioned in comments is not duplicate at all.

The scale does not change because I assume you are doing the weighing in open atmosphere where everything including your beaker, ball, even scale are already immersed in air. The open spaces are already fully filled with air. The atmospheric pressure being everywhere, the bernoulli's principle is not applicable, or in other words, it applies to everything involved and cancels out.

So, your observation is correct and reasonable - in case you the weighing is taking place in open air.

kpv
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