Weighing Ones Self

[weecalf]

Ok so you weigh your self and for sake of argument sake you are 11. 7 pounds .So as an experiment on behalf of the good people of Answerback I have weighed myself then weighed myself holding a 2 pound bag of sugar and sure enough the scales registered it although my hands were by my side and out side the width of the scales .How did that happen ?

[EDDIE51]

Your arms are attached to your body! so the weight of your arms is part of your body weight. Wearing shoes on the scales will show the weight of you plus the weight of the shoes, it does not matter if the sole of the shoe is soft or hard it still transmits the weight to the scales or what ever you are standing on.
Sorry but I am sure this is a joke, no one could seriously think that by holding your arms out by your side you can decrease your weight!
If that was true , then by holding weights in your outstretched arms that were equal to your body weight , you would become weightless and float off into the air!

[ummmm]

I'm surprised by that, Retrochic, I thought you had more common sense.

[Baldric]

Many thanks Jim, I guess I will have to include a ;-) to indicate the T I C element in any future posts.
;-)

[jennyjoan]

My mum was obsessed with her weight.

There lying in our bedroom I would be reading my Dandy or Beano - when the woman was standing naked staring at the reading. I used to say "mum your body is like the world" - is that right love. yes your breasts are coconuts from a coconut tree from America, your stomach is like a trammy line of all the countries (stretch marks) and beneath it all there likes your bush from Africa. Don't think she understood half of it.

[jim360]

Well it wasn't impossible that you were asking seriously, although perhaps I should have noticed that this thread was at least 50% non-serious. Still, perhaps someone was actually interested in the answer to your question. I live in hope!

[Retrochic]

jim I totally agree with your theory about it not being taught correctly in school. I went to an all girls school and physics was only on the curriculum up to 3rd year (year 8?) and taught with very little enthusiasm.

[Khandro]

The scales are standing on the floor of your house, which travelling sideways at 1,000 mph. depending on your point of view - but that's another story.

[Khandro]

Jim; Since posting the above I've been walking along the river and thinking; does sideways motion reduce downward motion? Isn't that why racing cars have aerofoils to keep them in contact with the ground?
If you fixed scales to a toboggan, would a child sitting on them (it) register as weighing less at speed?

[Old_Geezer]

Aerofoils change the airflow to provide downward pressure. Not sure that's anything to do with sideways motion affecting downward motion as such, it's about taking energy from the flow to create that extra pressure.

[Khandro]

OG; But doesn't a runner apply less pressure to the ground the faster (s)he runs?

[bhg481]

Khandro - you're only travelling at 1000mph if you are on the equator, anywhere else your speed is 1000 x cos(latitude). If you are running then your centrifugal force throwing you away from the centre of the earth will affect your weight but, depending on whether you're running east to west or west to east it will either decrease or increase it; in either case the change would be so small that you would not notice it.
As AOG says, aerofoils use air flow to help keep a car on the ground or help an aeroplane leave it.

[jim360]

Motion/ forces in different directions can indeed mix to some extent and make for some very complicated and bizarre effects. However a force that's applied truly in a horizontal direction will have no effect on the vertical forces, and in balancing them you should consider horizontal and vertical as separate directions.

The real world is never so perfect, so it's hard to say in practice. However I expect that a runner isn't so much exerting less pressure on the ground; rather, he is spending less time exerting that pressure. Overall this might give an appearance that he'd be lighter if weighed, but he isn't really. Since you couldn't actually weigh him in any meaningful sense while he's running it's a bit hard to confirm this. And also possibly the effect of wind flow might even make your runner appear heavier. Or lighter, depending on the dynamics of the thing.

Planes can fly because in some sense they weight as much as air does, when flying (at least the overall downward force is much less than the true weight). Formula One cars are designed to increase the downforce, which amounts to making it seem like the car weighs more when it's moving (increases the stability when going round corners, I think).

TLDR; it depends. Real motion is complicated.

[Peter Pedant]

No Jim
or perhaps yes Jim

I have read your answers as serious - the rest of us can make up the crass witless remarks as fillers

[Khandro]

jim; //you should consider horizontal and vertical as separate directions.//
Well of course, but surely the higher the velocity of mass moving horizontally, the less is the gravitational pull, and therefore its vertical weight is reduced.
A bullet starting on its forward movement from a gun barrel must have virtually no 'weight' relatively speaking. Isn't its trajectory formed by it loosing velocity and therefore it descends by gravitational pull?

[Hopkirk]

My brain hurts

[jim360]

No, that's not right at all. Gravity acts on on object no matter how fast it's travelling, and if there are no aerodynamic effects that might keep it up, then the speeding object falls just as fast to Earth as a non-speeding object would. There's a lovely video demonstration of this effect somewhere, but I can't find it.

At any rate, speeding objects don't experience less gravity. Total misconception there, I'm afraid, Khandro.

[Hopkirk]

What weighs more, a hundredweight sack of coal or a hundredweight sack of feathers?

[Dizmo]

Hopkirk: That's as nearly as bad as me asking how much batteries are at the pound shop. Or what time the 24/7 supermarket is open till.

[EDDIE51]

The instant a bullet leaves the gun barrel it is falling down under the influence of gravity , the forward speed does not alter the fall due to gravity.

[jim360]

Long or short hundredweight?

Assuming a perfect vacuum, then the bullet fired from a gun should have an essentially constant horizontal speed. It will still fall to the ground under the influence of gravity. The only reason is might seem to stay in the air longer is because it's travelled a rather greater distance along the ground, which people tend to translate into spending a greater amount of time in the air. Not so -- a ball dropped from 1m and a bullet fired from 1m both hit the ground roughly 1/5 of a second later.