At least how I learned physics, “weight” is formally defined as the normal force exerted by a surface on an object. Assuming an object resting on a surface in magical physics land (where lines are really parallel, skydivers can somehow get high enough to skydive with no air to cause resistance, etc), this will usually be F[sub]g[/sub] (the force of gravity = -mg, where g is acceleration due to gravity and the coordinate system grows upwards). However, if more downward force is exerted for whatever reason, you will weigh more (and if you have upward force exerted, you weigh less).
Thus anything floating does not have a surface to rest on and thus has no normal force exerted on it, and so it has no weight by definition.
When I try to hit a golf ball, it doesn’t matter whether there is a huge golf course, a tree, or a barn directly in front of me. I think golf balls must be 99.999% air.
There’s a lot of things other than paper in paper. For a smooth, bright sheet often papermakers will use calcium carbonate as filler. Most of your ash is probably calcium oxide. There are also trace minerals in the paper left over from the tree that show up as ash.
I jump up in the air, no my weight isn’t applying force to anything. However, my mass is still subject the the force of gravity giving me weight. If I come back down on a scale, the force on the scale will be the sum of my weight and momentum. The scale reading will fluctuate through the cycle of me jumping and coming back down. I will still have weight as long as I am in any field of gravity.
Real physicists, feel free to correct me if/where I’m wrong in this, it’s been a while since I studied any of this.
When in free-fall you’re “weightless”. So on the way back down from your jump you would be weightless. But some might also still say you have weight - that depends on whether you define weight as the force of gravity acting on you or the effective force which you only feel when something is stopping you falling, e.g. the Earth’s surface.
This is not true. Your weight depends on the gravity of wherever you are. This means your weight decreases as your altitude increases. (In fact, a lot of weightlessness in space is close enough to the Earth the effects of gravity are still very significant. The only thing that stops those spacecraft from hitting the Earth’s surface is that their trajectory and speed allow them to continually free-fall around the Earth (i.e. orbit) which actually requires gravity).
What that also means that if you’re on the Moon, for example, your weight is 1/6 what it is on the surface of the Earth.
Mass, however, doesn’t change (and that’s what most people mean by “weight” in common parlance).
All of this also means is that if you use the first definition of weight, the smoke is not weightless simply because it’s rising, and if you use the second definition the smoke actually has more weight because its movement is against gravity.
Since no one has related the story of Sir Walter Raleigh’s bet with the Queen, I’ll be the guilty one…
One day Raleigh made a wager he could weigh the smoke coming from his pipe. The Queen accepted the bet. Raleigh thereupon weighed a small quantity of tobacco, smoked it all, and then carefully weighed the ashes. The difference between the weight of the tobacco and the weight of the ashes, he said, must be the weight of the smoke. The Queen laughingly paid the wager, and said that many alchemists had turned gold into smoke, but Raleigh was the first to turn smoke into gold.
Clever - and scientifically accurate by the standards of the time - but ignoring, as we have said, the significant weight of the oxygen in both the ash and the smoke.
I’ve never seen that definition used, and I can’t see how it would be a very useful one. If I lean up against a wall, the surface of the wall is exerting a normal force on me, but I don’t think it makes anything clearer to call that normal force a “weight”. We already have a perfectly good word for normal forces: Just call them normal forces.
Yea, I know, I’ve burned magnesium in a crucible with an air tight lid, too. But the OP didn’t specify air tight crucibles, just “if I burn 5 pounds of paper”…sort of like…“in the fireplace”.
Both of the physics textbooks I have lying around call the normal force “weight”* and alternately use w and F[sub]n[/sub] to denote it. Upon looking online, it appears that this is one of the common ways to define weight (known as the “operational definition” on Wikipedia). However, other sources call this the “apparent weight” and define |F[sub]g[/sub]| as the weight. So I guess it depends who you’re talking to.
Reasoning that feeling a normal force acting on you causes the feeling of weight, while freefalling causes a feeling of “weightlessness”
No, when I am in free fall in any field of gravity, my weight overcomes my momentum to accelerate my rate of fall. Which way, if any, we move depends on the sum of the forces on us.
Back closer to topic. Crucible? Burned many circles of ashless, low ash?, filter paper in them.
