Csail
N/A
Kids party on saturday so i'm going to try the experiment, they normally get helium balloons.
Centrifugal Force - one for the physicists!
- Thread starter DaveS
- Start date
matelot
New member
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Not being argumentative but I dont believe your observations of the balloon can be correct Dave. If they were they would defy Newtons first law " corpus omni ..... ".
The balloon will try to go straight on when the car starts to corner. to get the balloon to go round the corner requires application of a force to it which is done with the string which will be at an angle to the vertical leaning outwards. This angle will be minimised because there is a force lifting the balloon above the hand holding the string - buoyancy. But it will always be an angle outwards or the balloon wont go round the corner.
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You would think so, wouldn't you? That was why the first time I noticed that the string leans inwards I was surprised.
Thanks to Mobydick, Snowleopard and Peterb for pointing out my fore / aft error. The balloon's behaviour within an accelerating mass of air is indeed different from that seen when it is being accelerated through stationary air.
I can understand the buoyancy argument and the parallel with spirit levels. All are variations of saying that perceived "local gravity" (vector sum of real gravity and applied acceleration) is acting at an angle to the vertical. OK, I concede, the phenomena is caused by the centripetal acceleration of the air within the car, and it can be explained without invoking centrifugal force. Curses! /forums/images/graemlins/frown.gif
Now what happens if you try it with the car windows open so that the air is not trapped? /forums/images/graemlins/grin.gif
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Isnt it weird how you brain continues to (try to) work when you're asleep? I woke up at 3 am last night realising I had written a lot of rubbish in saying the balloon must go outwards. You are of course accelerating a car full of air round that bend, so to use the engineers concept of centrifugal force the heavy air will be forced outwards more than the lighter helium. As I guess other cleverer people than me have already said.
I really must learn only to post when the brain has been fully engaged. /forums/images/graemlins/blush.gif
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Not being argumentative but I dont believe your observations of the balloon can be correct Dave. If they were they would defy Newtons first law " corpus omni ..... ".
The balloon will try to go straight on when the car starts to corner. to get the balloon to go round the corner requires application of a force to it which is done with the string which will be at an angle to the vertical leaning outwards. This angle will be minimised because there is a force lifting the balloon above the hand holding the string - buoyancy. But it will always be an angle outwards or the balloon wont go round the corner.
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You would think so, wouldn't you? That was why the first time I noticed that the string leans inwards I was surprised.
Thanks to Mobydick, Snowleopard and Peterb for pointing out my fore / aft error. The balloon's behaviour within an accelerating mass of air is indeed different from that seen when it is being accelerated through stationary air.
I can understand the buoyancy argument and the parallel with spirit levels. All are variations of saying that perceived "local gravity" (vector sum of real gravity and applied acceleration) is acting at an angle to the vertical. OK, I concede, the phenomena is caused by the centripetal acceleration of the air within the car, and it can be explained without invoking centrifugal force. Curses! /forums/images/graemlins/frown.gif
Now what happens if you try it with the car windows open so that the air is not trapped? /forums/images/graemlins/grin.gif
[/ QUOTE ]
Isnt it weird how you brain continues to (try to) work when you're asleep? I woke up at 3 am last night realising I had written a lot of rubbish in saying the balloon must go outwards. You are of course accelerating a car full of air round that bend, so to use the engineers concept of centrifugal force the heavy air will be forced outwards more than the lighter helium. As I guess other cleverer people than me have already said.
I really must learn only to post when the brain has been fully engaged. /forums/images/graemlins/blush.gif
O
Oldhombre
Guest
So basically if you leave a helium filled balloon in your forecabin, as you ride over a wave, the air in the cabin is forced up as the hull drops down and the helium balloon is thus forced down, all that is fine but when the helium balloon then contacts the cabin sole does that increase or decrease the mass of the falling hull, or in other words does the balloon act as a damper to wave motion or does it make it worse?
Is there an analogy with half filled holding tanks and do we therefore have to take care about our diet when heading for rough water?
Or is it all a load of poo?
Is there an analogy with half filled holding tanks and do we therefore have to take care about our diet when heading for rough water?
Or is it all a load of poo?
matelot
New member
It should act as a damper unless the period of the sloshing around in the holding tank co-incides with that of the boat when you might get feedback and the whole system go into oscillation. The end result will be you disappearing in a shower of sh.. /forums/images/graemlins/laugh.gif
peterb
New member
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So basically if you leave a helium filled balloon in your forecabin, as you ride over a wave, the air in the cabin is forced up as the hull drops down and the helium balloon is thus forced down, all that is fine but when the helium balloon then contacts the cabin sole does that increase or decrease the mass of the falling hull, or in other words does the balloon act as a damper to wave motion or does it make it worse?
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I can assure you (by experiment) that if the cabin is in free-fall then the balloon will float freely with no tendency to either rise or fall relative to the cabin. We tried it (as an incidental interest) during parabolic flight in tests for the European Space Agency. But if the cabin were to drop faster than under normal gravity, then you would hit the ceiling and the balloon would hit the floor (also experimentally tested!).
So basically if you leave a helium filled balloon in your forecabin, as you ride over a wave, the air in the cabin is forced up as the hull drops down and the helium balloon is thus forced down, all that is fine but when the helium balloon then contacts the cabin sole does that increase or decrease the mass of the falling hull, or in other words does the balloon act as a damper to wave motion or does it make it worse?
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I can assure you (by experiment) that if the cabin is in free-fall then the balloon will float freely with no tendency to either rise or fall relative to the cabin. We tried it (as an incidental interest) during parabolic flight in tests for the European Space Agency. But if the cabin were to drop faster than under normal gravity, then you would hit the ceiling and the balloon would hit the floor (also experimentally tested!).
tangomoon
New member
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This should be a good time of year for balloons - taxi back from Xmas party maybe?
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Will do!
Have a good Christmas!
This should be a good time of year for balloons - taxi back from Xmas party maybe?
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Will do!
Have a good Christmas!
cnh
New member
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This is one of the nastiest bit of 'physics' that I have read for some time.
If there were an equal and opposite force, the Moon would not orbit the Earth!
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Ought we to advise the NOAA they have it wrong?
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If I had the energy to do so - but it's such a common misconception, it's like banging your head against the proverbial wall.
If you can find any physicist who would endorse the statement, I'd be very surprised.
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This is one of the nastiest bit of 'physics' that I have read for some time.
If there were an equal and opposite force, the Moon would not orbit the Earth!
[/ QUOTE ]
Ought we to advise the NOAA they have it wrong?
[/ QUOTE ]
If I had the energy to do so - but it's such a common misconception, it's like banging your head against the proverbial wall.
If you can find any physicist who would endorse the statement, I'd be very surprised.
mobeydick
Member
Of course the forces are equal and opposite. If they were not, the system would not be in equilibrium!
md
md
matelot
New member
At the risk of shooting myself in the foot the second time round,, I would argue that point.
What is happening with the moon orbiting the earth (and actually they are both orbiting a common c of g) is that the moon is continually changing its flight vector and so is accelerating. gravitational attraction provides the force that creates this acceleration - without it the moon would just bugger off in a straight line.. there is no other force involved but gravity and that only works one way. arguably the system isnt in equilibrium so much as constant consistent change.
now go on and show me how I've missed the point a second time. /forums/images/graemlins/blush.gif
What is happening with the moon orbiting the earth (and actually they are both orbiting a common c of g) is that the moon is continually changing its flight vector and so is accelerating. gravitational attraction provides the force that creates this acceleration - without it the moon would just bugger off in a straight line.. there is no other force involved but gravity and that only works one way. arguably the system isnt in equilibrium so much as constant consistent change.
now go on and show me how I've missed the point a second time. /forums/images/graemlins/blush.gif
cliffordpope
New member
If the earth suddenly vanished, surely the moon would initially continue on its path, but it would be on the wrong orbit to continue sustainably? It was only "orbitting" the sun because the much nearer earth was forcing it to - on its own there would be insufficient gravitational pull and it would fly off into space, or into another orbit much further out from the sun?
peterb
New member
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If the earth suddenly vanished, surely the moon would initially continue on its path, but it would be on the wrong orbit to continue sustainably? It was only "orbitting" the sun because the much nearer earth was forcing it to - on its own there would be insufficient gravitational pull and it would fly off into space, or into another orbit much further out from the sun?
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Yes, the gravitational pull on just the moon would be less than on the Earth and moon combined. But the mass on which that pull is operating would be reduced in the same ratio. Since the acceleration of the moon is the ratio of the force to the mass, the nett effect would be that the acceleration towards the sun would be the same. Fortunately, however, the Earth is unlikely to suddenly vanish!
If the earth suddenly vanished, surely the moon would initially continue on its path, but it would be on the wrong orbit to continue sustainably? It was only "orbitting" the sun because the much nearer earth was forcing it to - on its own there would be insufficient gravitational pull and it would fly off into space, or into another orbit much further out from the sun?
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Yes, the gravitational pull on just the moon would be less than on the Earth and moon combined. But the mass on which that pull is operating would be reduced in the same ratio. Since the acceleration of the moon is the ratio of the force to the mass, the nett effect would be that the acceleration towards the sun would be the same. Fortunately, however, the Earth is unlikely to suddenly vanish!
cnh
New member
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Of course the forces are equal and opposite.
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If the forces on the moon were equal and opposite, it would travel in a straight line. it does not. It travels in a circle. A force is needed to do that. The moon is not 'in equilibrium' but the earth/moon system as a whole is (well, not quite, since they also orbit the sun).
And the moon would not 'fly out into space' if the earth disappeared. It would continue to orbit the sun in some elliptical orbit.
Of course the forces are equal and opposite.
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If the forces on the moon were equal and opposite, it would travel in a straight line. it does not. It travels in a circle. A force is needed to do that. The moon is not 'in equilibrium' but the earth/moon system as a whole is (well, not quite, since they also orbit the sun).
And the moon would not 'fly out into space' if the earth disappeared. It would continue to orbit the sun in some elliptical orbit.
matelot
New member
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If the earth suddenly vanished, surely the moon would initially continue on its path, but it would be on the wrong orbit to continue sustainably? It was only "orbitting" the sun because the much nearer earth was forcing it to - on its own there would be insufficient gravitational pull and it would fly off into space, or into another orbit much further out from the sun?
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yes and no. what peterb says sounds right to me.
P.S. Whats all this about the earth vanishing? Do you know something that we dont? Dont you believe Gordy when he says he's saved the world?
If the earth suddenly vanished, surely the moon would initially continue on its path, but it would be on the wrong orbit to continue sustainably? It was only "orbitting" the sun because the much nearer earth was forcing it to - on its own there would be insufficient gravitational pull and it would fly off into space, or into another orbit much further out from the sun?
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yes and no. what peterb says sounds right to me.
P.S. Whats all this about the earth vanishing? Do you know something that we dont? Dont you believe Gordy when he says he's saved the world?
cliffordpope
New member
The earth has already vanished. It is simply a bookeeping concept representing the discounted future value of a toxic asset in negative equity.
What the moon sees in us, heaven knows.
What the moon sees in us, heaven knows.
matelot
New member
your last sentence sounds just like my wife
O
Oldhombre
Guest
Remember that everything you see is in the past. The speed of light ensures that fact. But, if looking to your left is in the past and looking to your right is also in the past, where does that leave you, the observer ?
boatmike
Well-known member
From an engineers point of view is it not a simple matter of relative mass?
A body with high mass (lets say heavy its easier) swung around on a bit of string at a constant speed will result in a force being exerted on the string. A lighter body will exert a lower force. What we have here are two bodies of different mass attached by a string between them. Also one is lighter than air so effectively the upward forces are greater than the gravitational forces acting upon it where the other is affected entirely by gravity. The friction of air acting on the balloon will have a big effect if the balloon is outside the car of course but if inside it won't....
So assuming the speed of the car to be uniform (no accelleration) There will be a simple force acting on the string and the string will be vertical. When the car corners the sideways force on the car is higher than the sideways force on the balloon making it lean inwards...... I think /forums/images/graemlins/tongue.gif /forums/images/graemlins/tongue.gif
A body with high mass (lets say heavy its easier) swung around on a bit of string at a constant speed will result in a force being exerted on the string. A lighter body will exert a lower force. What we have here are two bodies of different mass attached by a string between them. Also one is lighter than air so effectively the upward forces are greater than the gravitational forces acting upon it where the other is affected entirely by gravity. The friction of air acting on the balloon will have a big effect if the balloon is outside the car of course but if inside it won't....
So assuming the speed of the car to be uniform (no accelleration) There will be a simple force acting on the string and the string will be vertical. When the car corners the sideways force on the car is higher than the sideways force on the balloon making it lean inwards...... I think /forums/images/graemlins/tongue.gif /forums/images/graemlins/tongue.gif
thefatlady
Well-known member
At the centre of my universe.
boatmike
Well-known member
...............the discounted future value of a toxic asset in negative equity.
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Is that 42???? /forums/images/graemlins/confused.gif
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Is that 42???? /forums/images/graemlins/confused.gif
Ardenfour
Active member
Just read all this - don't need baloons, when I have the heater on I get a waft of warmer air round a right hand corner as the denser cold air is flung outwards. Round a left hander the cooler denser air displaces the warmer to the passenger side, same as yer baloons, et al
