Do Floating Objects Have 'Weight'?

[inventor]

OK, so an aircraft, upon landing, its wheels aren't moving. Therefore, the aircraft must stop instantly upon contacting the runway.
Or, the aircraft is propelled by the engines, and the speed at which the wheels are rotating is irrelevant.

 

[Walter]

You just contradicted yourself, Walter...

I don't see it, please explain.

 

[Blackwood]

Everything with mass within a finite distance of anything else with mass has weight.

The plane takes off because the the engine pushes it forward, not the wheels.

/thread

 

[CT Sean]

Originally Posted by Walter
A scale calibrated in kilos (mass) for use on earth would be wrong on the moon, but a scale calibrated in pounds (weight) would still be correct on the moon. Weight changes depending on the gravitational field, mass does not.

You just contradicted yourself, Walter...

Peace,
Greg

I don't see it, please explain.

I don't think it's exactly exactly a contradiction but what is implied is that given two otherwise identical scales - one in kilos and one in lbs, the statement is that on earth, they will indicate I will weigh 82 kg and 180 lbs respectively (which they will - because I do)

now I take those two scales to the moon, the scale calibrated in lbs will say I weigh 30 lbs, but the kilogram scale will still say 82 Kg which is not correct - it will read about 14.

 

[DennisW]

If an object has mass (most objects do) and gravity is operational, then the object has weight. So, even though an object is floating in water (even an object that is neutrally bouyant), it has mass and gravity is acting on it, so it has weight.

 

[smellzlikefish]

Quote:
Originally Posted by Walter
A scale calibrated in kilos (mass) for use on earth would be wrong on the moon, but a scale calibrated in pounds (weight) would still be correct on the moon. Weight changes depending on the gravitational field, mass does not.
Quote:
Originally Posted by kanonfodr
You just contradicted yourself, Walter...

Peace,
Greg
Quote:
Originally Posted by Walter
I don't see it, please explain.

I don't think it's exactly exactly a contradiction but what is implied is that given two otherwise identical scales - one in kilos and one in lbs, the statement is that on earth, they will indicate I will weigh 82 kg and 180 lbs respectively (which they will - because I do)

now I take those two scales to the moon, the scale calibrated in lbs will say I weigh 30 lbs, but the kilogram scale will still say 82 Kg which is not correct - it will read about 14.

Right, except that kg is a measure of mass while lbs is a measure of weight (takes into account gravity). For most purposes, kg can be measured on a scale because not many of us leave the earth's surface, but traditionally kg should be weighed on a balance which measures one mass in relation to another and isn't affected by gravity.

 

[CT Sean]

Right, except that kg is a measure of mass while lbs is a measure of weight (takes into account gravity). For most purposes, kg can be measured on a scale because not many of us leave the earth's surface, but traditionally kg should be weighed on a balance which measures one mass in relation to another and isn't affected by gravity.

I totally understand and agree, but for the example given, "a scale calibrated...", the scale type has to be the same or the example is invalid. You can't say " a scale calibrated in kilos AND happens to be a balance scale" vs "a scale calibrated in lbs and happens to be a digital bathroom scale". that's not an apples to apples comparison.

Something tells me this level of discussion isn't at all what the OP had in mind when the question was asked .

 

[Blackwood]

Something tells me this level of discussion isn't at all what the OP had in mind when the question was asked .

But as is generally the case, he got his answer in Post #2. :cool2:

 

[The Kraken]

Everything that is physical in nature has weight. Each and every atom has weight.

Do not misconstrue buoyancy with weight.

But a more practical test might be warranted.

Take that that aircraft carrier out of the water and drop it on your toe. Does it have weight?

the K

 

[Walter]

I don't think it's exactly exactly a contradiction but what is implied is that given two otherwise identical scales - one in kilos and one in lbs, the statement is that on earth, they will indicate I will weigh 82 kg and 180 lbs respectively (which they will - because I do)

now I take those two scales to the moon, the scale calibrated in lbs will say I weigh 30 lbs, but the kilogram scale will still say 82 Kg which is not correct - it will read about 14.

That's because I did not contadict myself, but kanonfodr obviously sees something I'm not seeing. I strongly suspect he's making a mistake, but I'm open to the possibility the mistake was mine. It wouldn't be the first time...

To avoid confusion, let's refer to devices that do not use a balance to determine weight as a scale and devices that do use a balance as a balance. A scale calibrated in lbs will say you weigh 180 lbs on Earth and 30 lbs on the moon. Both will be correct because weight changes with changes in gravity. The moon's gravity is ≈ one sixth that of Earth's. A scale calibrated in kilos will say your mass is 82 kg. That same scale on the moon will say your mass is 14 kg. That scale will be incorrect as your mass would not have changed. A balance calibrated in kg will be correct on both the Earth or the moon. A balance calibrated in lbs will be off on the moon (unless it was calibrated for the moon).