Everyday science: Why do we weigh less in water?

Updated: Oct 9, 2019

While you may weigh (kg) the same in water, thanks to upward buoyant forces and drag (resistance), gravity's effect is not so noticeable.

A student once asked me whether they weighed less in #water and more when they were falling through the #air. While it may appear that you weigh less in water, you actually weigh the same if you were standing on a set of #scales.

To prove it, if you were able to #submerge yourself in a tub of #water on a set of scales, you would find that the total weight (w) would be #equal to your weight (Wx) plus the weight of the water (Wy) : Wy+Wx=Tw

So while it may seem you weigh less in water, you are still exerting the same downward #pressure onto the scales.

Same goes if you are falling through the air, your #weight is constant and unchanging. If you weigh 80kg #falling out of the #plane, you will consistently weigh 80kg on the way down #displacing air on your way through.

When falling through the air the upward buoyant forces and drag (resistance) are less than in water and gravity's effect is more noticeable.

In this case you’re #exerting downward pressure over a much larger area, but hypothetically if we could contain you (Wx) and the air (Wy) in a #container on a set of scales, the same total weight would be observed : Wy+Wx=Tw

So this leaves an interesting #question. Given we know anything #submerged in a fluid #displaces it, how much higher is the sea #level today due to #human made #submersibles? Is melting #ice the only thing we should worry about?

Nick Griffin

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