Is a dinghy heavier when inflated?

As LW395 pointed out, my "Fag packet" calc. gave a typical increase in mass of about 3.5 kg and an increase in weight of 1.2 kg but volume was grossly overestimated.
If I scale back inflated volume by a factor of about 3 the increase in mass is still greater than 1kg, but the increase in angular momentum of the entire package is still significant - making the dinghy much harder to start moving and conversely, stop.

In addition, of course, to the physical handling thing....

Anyhoo - 1/2 bottle Aussie red later, I think we've wrung out all the interest to be got, and I'm NOT goin' out to weigh dinghies this time of night.
 
I was intrigued by the mention of mass versus weight. He is right of course. Imet a bloke once who flew hot air balloons it talked of the mass of a big one being some 20 tonnes. The weight was 0 or negative hence it flew. You really notice the huge mass though when it is moving along in a breeze and you try to stop it. Then you notice the inertia of 20 tonnes.
Likewise a party balloon has a significant inertia when moving even though near 0 weight. Just thought someone might be interested.
Regarding the dinghy the increase in weight is only the weight of the air in the balloon that is more than 1 bar or the weight of about .5 psi of air in the dinghy. ie very little. olewill
 
Exactly, the Hindenberg weighed nothing, but I wouldn't have stuck my head between it and its mooring post!

More importantly (from the point of view of our dinghy) imagine a 1 kg bag of sugar (representing the mass of air you added to the dinghy by inflating it)... you can spin it about its own axis - no problem.
But in an inflated dinghy the mass is distributed as if it was 1/2 kg at each end of a pole maybe 1/2 the length of the dinghy, about 1.5 metres. NOW start (or stop) it spinning.
Much more difficult!
Of course the mass of the inflated dinghy ITSELF is now spread over a bigger "disc" and so the angular momentum (second moment of inertia keeps springing to my alcohol-addled mind?) of the entire system is massively greater than a deflated, packed dinghy.

Physics in action!
 
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Scope here for the intrusion of mere pragmatism. Weigh it. Pump it up. Weigh it again.

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This will NOT give you an answer as to how much more effort it will be to handle when inflated. Only a quantitative measure of weight, which is not the whole story.
 
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So what if you filled it with helium??

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Someone tried this racing Zapcats..little difference and IIRC boat deflated as material was porus to helium?
 
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Exactly, the Hindenberg weighed nothing, but I wouldn't have stuck my head between it and its mooring post!


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Gives a new meaning to the phrase "Are your ears burning! /forums/images/graemlins/blush.gif
 
Just caught this as it slipped into oblivion..

Obviously I was referring to getting crushed by the 130 tons of mass of the thing, not getting toasted! /forums/images/graemlins/ooo.gif
 
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