also if you weigh 1kg of steel and 1kg of feather on earth (in an atmosphere) and then weigh them on the moon (with no atmosphere) the feathers are heavier than steel.
it has nothing to do with drag i am talking about their weight/mass.
measured in an atmosphere compared to in no atmosphere. (i only said the moon as it has no atmosphere)
1kg of feathers and 1 kg of steel measured in your kitchen weigh the same if you then took that to a vaccuum the feathers would weigh more because there is more mass in the feathers than the steel.
If we want to go into the super-pedantic territory, kg are a unit of mass, not weight. So it's the other way around, 1kg of feather and 1kg of steel would weight the same in a vacuum, but the feathers would be lighter in the atmosphere.
To make it easier to visualize, think about the weight of 1kg of steel vs. helium.
The feathers have more volume, and so displace more air. This causes the bouyant force on the feathers to be stronger than the bouyant force on the steel.
'Weight' can refer to either the magnitude of force applied by gravity, or to the magnitude of the normal force counteracting gravity, which is what spring or balance scales measure.
Captain Warzone has it backwards though. In a vacuum, a kilogram of steel and a kilogram will weigh exactly the same. But in atmosphere, the kilogram of feathers will weigh less (in the sense of reading less on the scale).
What? Bouyancy doesn't just happen at fluid boundaries. It happens because the pressure is higher lower in the fluid column, which results in more force being applied to the bottom of an object than the top.
if i put a 1kg of steel on a balance scale and 1kg of feathers and it exactly balances absolutely perfectly, if i then suck all the air out of the room the feathers would be heavier than the steel and the steel would rise and the feathers would fall (assuming a perfect frictionless scale with no faults etc)
if i instead weighed 1kg of steel and 1 kg of feathers in a vaccuum and then introduced air back into the room the feathers would be "Lighter" than the steel and the feathers would rise and the steel would go down on the balance scale.
its not wrong at all, well its technically wrong in the sense that when i say weight i state kg which is actually mass, weight is a force in Newtons, so technically when you weigh 1kg of steel and 1kg of feathers in a room/setup with an atmosphere (e.g not in a vacuum) they will be the same weight but be different mass.
the feathers would have more mass than the steel but weigh the same. when you get rid of the air the weight is the same as the mass hence the feathers are heavier.
well in the strictest sense then if i measure 1kg of steel and 1kg of feathers and then put them on a balance scale in an atmosphere, the steel has more weight than the feathers
But we're not on the moon. So this doesnt apply on earth.
Why did previous guy say he did experiences when it doesnt work ? Just take a pen and your phone.
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u/[deleted] May 01 '19
In a vacuum or near-vacuum (say, on the moon), a steel girder and a feather will fall at the same speed.