# weight after burning **URL:** \ **Category:** Factual Questions\ **Created:** [February 13, 2012, 5:50am UTC](https://boards.straightdope.com/t/weight-after-burning/612683 "2012-02-13T05:50:09Z")\ **Posts on this page:** 12\ **Page:** 3
**Author:** ![Jragon](https://avatars.discourse-cdn.com/v4/letter/j/e19b73/32.png) [@Jragon](https://boards.straightdope.com/u/Jragon)\ **Post date:** [February 14, 2012, 5:17am UTC](https://boards.straightdope.com/t/weight-after-burning/612683/41 "2012-02-14T05:17:29Z")
> [@Chessic\_Sense](#): > > Um…what? Things don’t stop having weight just because they’re being moved around. If I jump up and down on a scale, the needle will move, but that’s just because it’s not a perfect measuring device. I still weight the same thing throughout the jump. 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. ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [February 14, 2012, 11:42am UTC](https://boards.straightdope.com/t/weight-after-burning/612683/42 "2012-02-14T11:42:20Z")
> [@Bill\_Door](#): > > I’ve heard that quote, “90% of a tree is air”, but did you ever try to hit a golf ball through one? Every stinkin’ time I hit the part made out of wood. Statistically improbable, but true. 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. ---
**Author:** ![Bill\_Door](https://avatars.discourse-cdn.com/v4/letter/b/50afbb/32.png) [@Bill\_Door](https://boards.straightdope.com/u/Bill_Door)\ **Post date:** [February 14, 2012, 12:33pm UTC](https://boards.straightdope.com/t/weight-after-burning/612683/43 "2012-02-14T12:33:16Z")
> [@copperwindow](#): > > Well then, what is the ash made out of? Why didn’t all of the paper get converted to CO2? 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. ---
**Author:** ![thelabdude](https://avatars.discourse-cdn.com/v4/letter/t/dc4da7/32.png) [@thelabdude](https://boards.straightdope.com/u/thelabdude)\ **Post date:** [February 14, 2012, 1:56pm UTC](https://boards.straightdope.com/t/weight-after-burning/612683/44 "2012-02-14T13:56:48Z")
> [@Jragon](#): > > 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. 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. ---
**Author:** ![Bozuit](https://avatars.discourse-cdn.com/v4/letter/b/edb3f5/32.png) [@Bozuit](https://boards.straightdope.com/u/Bozuit)\ **Post date:** [February 14, 2012, 2:53pm UTC](https://boards.straightdope.com/t/weight-after-burning/612683/45 "2012-02-14T14:53:13Z")
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. > [@Chessic\_Sense](#): > > Um…what? Things don’t stop having weight just because they’re being moved around. If I jump up and down on a scale, the needle will move, but that’s just because it’s not a perfect measuring device. I still weight the same thing throughout the jump. > [@thelabdude](#): > > 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. 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. > [@thelabdude](#): > > I will still have weight as long as I am in any field of gravity. 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. ---
**Author:** ![Dufus](https://avatars.discourse-cdn.com/v4/letter/d/c77e96/32.png) [@Dufus](https://boards.straightdope.com/u/Dufus)\ **Post date:** [February 14, 2012, 3:12pm UTC](https://boards.straightdope.com/t/weight-after-burning/612683/46 "2012-02-14T15:12:19Z")
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. ---
**Author:** ![copperwindow](https://avatars.discourse-cdn.com/v4/letter/c/4af34b/32.png) [@copperwindow](https://boards.straightdope.com/u/copperwindow)\ **Post date:** [February 14, 2012, 6:15pm UTC](https://boards.straightdope.com/t/weight-after-burning/612683/47 "2012-02-14T18:15:27Z")
> [@Bozuit](#): > > 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 m 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. Does this mean when Gringrich makes his moon colony, obesity will be a thing of the past? ---
**Author:** ![Malacandra](https://avatars.discourse-cdn.com/v4/letter/m/45deac/32.png) [@Malacandra](https://boards.straightdope.com/u/Malacandra)\ **Post date:** [February 14, 2012, 11:55pm UTC](https://boards.straightdope.com/t/weight-after-burning/612683/48 "2012-02-14T23:55:41Z")
> [@Dufus](#): > > 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. 🙂 ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [February 15, 2012, 12:09am UTC](https://boards.straightdope.com/t/weight-after-burning/612683/49 "2012-02-15T00:09:41Z")
> [@](#): > > Quoth **Jragon** : > At least how I learned physics, “weight” is formally defined as the normal force exerted by a surface on an object. 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. ---
**Author:** ![Dufus](https://avatars.discourse-cdn.com/v4/letter/d/c77e96/32.png) [@Dufus](https://boards.straightdope.com/u/Dufus)\ **Post date:** [February 15, 2012, 12:17am UTC](https://boards.straightdope.com/t/weight-after-burning/612683/50 "2012-02-15T00:17:47Z")
> [@Malacandra](#): > > 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. 🙂 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”. ---
**Author:** ![Jragon](https://avatars.discourse-cdn.com/v4/letter/j/e19b73/32.png) [@Jragon](https://boards.straightdope.com/u/Jragon)\ **Post date:** [February 15, 2012, 12:57am UTC](https://boards.straightdope.com/t/weight-after-burning/612683/51 "2012-02-15T00:57:02Z")
> [@Chronos](#): > > 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. 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” ---
**Author:** ![thelabdude](https://avatars.discourse-cdn.com/v4/letter/t/dc4da7/32.png) [@thelabdude](https://boards.straightdope.com/u/thelabdude)\ **Post date:** [February 15, 2012, 2:55am UTC](https://boards.straightdope.com/t/weight-after-burning/612683/52 "2012-02-15T02:55:42Z")
> [@Bozuit](#): > > 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. 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. [Previous page](https://boards.straightdope.com/t/weight-after-burning/612683.md?page=2)