Centrifugal Force - one for the physicists!

[Piers]

Onr of the best descriptions of the two 'bulges' is here.

In essence, the gravitational pull pulls the weater to one side of the earth, whilst the centrifugal force forces the water away from the other side.

All because the orbit of earth, moon and sun are balanced (plus a few more factors etc etc)

 

[bobgoode]

Balloon in car problem..explanation is the same as for the operation of the centrifuge....and does not require the introduction of centrifugal force. I know it's counter-intuitive but so is a lot of physics!

 

[Piers]

Chapter 2 states (under the heading Origin of the Tide-Raising Forces)

"To all outward appearances, the moon revolves around the earth, but in actuality, the moon and earth revolve together around their common center of mass, or gravity. The two astronomical bodies are held together by gravitational attraction, but are simultaneously kept apart by an equal and opposite centrifugal force produced by their individual revolutions around the center-of-mass of the earth-moon system. This balance of forces in orbital revolution applies to the center-of-mass of the individual bodies only. At the earth's surface, an imbalance between these two forces results in the fact that there exists, on the hemisphere of the earth turned toward the moon, a net (or differential) tide-producing force which acts in the direction of the moon's gravitational attraction, or toward the center of the moon. On the side of the earth directly opposite the moon, the net tide-producing force is in the direction of the greater centrifugal force, or away from the moon."

Courtesy of the NOAA

 

[cnh]

[ QUOTE ]
Chapter 2 states (under the heading Origin of the Tide-Raising Forces)

The two astronomical bodies are held together by gravitational attraction, but are simultaneously kept apart by an equal and opposite centrifugal force produced by their individual revolutions around the center-of-mass of the earth-moon system. This balance of forces in orbital revolution applies to the center-of-mass of the individual bodies only.
Courtesy of the NOAA

[/ QUOTE ]


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!

 

[Topcat47]

When you're driving along with a baloon out your car window, the predominant force acting on it is the draught. It's a poor analagy.

Better consider a conker on a string. If you whirl it around your head, in order to execute a circle, a force has to act upon the conker in the direction of the string, towards the centre of the circle. This is the centrepetal force on the conker.

As Newton states, for every action there is an equal and opposite reaction, which is what you know as the centrefugal force, and you notice it because it acts upon your wrist.

When the string brakes, the conker continues to fly in a straight line as a result of there being no centrepetal force acting on it.

 

[Topcat47]

By the way, the earth and moon are not in contrapuntal orbit around each other. The moon orbits the earth and the earth orbits the sun, dragging the moon with it. If the earth were to vanish in a puff of smoke, the moon would not continue to orbit the sun. If the moon were to be the one to disappear, the earth would still precess around the sun in more or less the same fashion.

 

[tangomoon]

[ QUOTE ]
Now take the ballon and sit in a car. When the car accelerates the ballon moves back, when braking it moves forward.

[/ QUOTE ]

Surely the balloon moves to the back of the car when you brake due to the air within having inertia and continuing forward, and the balloon reacts by floating toward the lowest pressure and lowest density air mass at the back of the car.

The 'leaning may be due to the same forces, centripetal pulling one part toward the centre and higher pressure at inside of outside of the car exerting force. Have to think on.

Kinetic energy too playing its part as an unblalanced force is in action.

Best you check your experiment thoroughly - It's only A-Level Physics but think I remember it correctly

 

[tangomoon]

[ QUOTE ]
Again, no surpises. Now go round a corner and watch what happens: the balloon leans into the bend, the string adopting the same angle to the vertical as a cyclist would!

[/ QUOTE ]

Sorry I am sure your statements are flawed.

The balloon would 'lean' out of the corner assuming it to be fastened to the interior by the string.

Bit of a cluster I'm afraid.

 

[cnh]

[ QUOTE ]
If the earth were to vanish in a puff of smoke, the moon would not continue to orbit the sun.

[/ QUOTE ]

Yes, it would.

Where else could it go?

Its exact orbit would depend on where it was relative to the Earth when the Earth vanished, but it would still orbit the Sun.

 

[DaveS]

[ QUOTE ]
[ QUOTE ]
Again, no surpises. Now go round a corner and watch what happens: the balloon leans into the bend, the string adopting the same angle to the vertical as a cyclist would!

[/ QUOTE ]

Sorry I am sure your statements are flawed.

The balloon would 'lean' out of the corner assuming it to be fastened to the interior by the string.

Bit of a cluster I'm afraid.

[/ QUOTE ]

I'm not quite sure what you mean by "bit of a cluster". Is this rhyming slang?

If you check back the various threads I think you'll find that, despite a confusing error in my OP which I admitted to some hours ago, we have now generally reached amicable agreement on why the balloon leans in, with an explanation (buoyancy within an accelerating air mass) which does not rely on centrifugal force - which was my original question. My supplementary query as to what happens when the air mass is less constrained remains unanswered, but that's a detail that could easily be tested practically.

Could I suggest that Matelot, cnh, and you, who all assert that the balloon will lean out, obtain a helium balloon on a string and try it? This should be a good time of year for balloons - taxi back from Xmas party maybe? /forums/images/graemlins/smile.gif

 

[machurley22]

Excellent thread and after a couple of false starts the explanation was found but it's amazing that it still continues with people, who presumably haven't read what's gone before, giving contrary views!

Could everyone please read Mobeydick's link before posting again on this thread. /forums/images/graemlins/cool.gif

 

[machurley22]

[ QUOTE ]
Surely the balloon moves to the back of the car when you brake due to the air within having inertia and continuing forward, and the balloon reacts by floating toward the lowest pressure and lowest density air mass at the back of the car.

[/ QUOTE ]
The balloon leans in to the corner for exactly the same reason.

 

[saltwater_gypsy]

What a great thread, erudite entertaining and not a cross word written ------and not a thing about sailing/boating.
Maybe thats the secret!!

 

[machurley22]

[ QUOTE ]
My supplementary query as to what happens when the air mass is less constrained remains unanswered...

[/ QUOTE ]
Pretty sure that the balloon would be sucked out of/towards any window you opened. This is the effect that allows us to sail to windward, or a meringue?

 

[Foxy]

Cool one! Well done whoever started.. Give us MORE!

 

[[2068]]

My only observation would be to take care when testing this theory out.

Otherwise there are going to be some perplexed road accident investigators trying to determine the significance of helium balloons found in a series of accidents.

"There appears to be a pattern: witnesses reported sharp braking, followed by fierce acceleration. The cars then left the road at high speed with smoke pouring off the tyres...."

 

[peterb]

[ QUOTE ]
My only observation would be to take care when testing this theory out.

Otherwise there are going to be some perplexed road accident investigators trying to determine the significance of helium balloons found in a series of accidents.

"There appears to be a pattern: witnesses reported sharp braking, followed by fierce acceleration. The cars then left the road at high speed with smoke pouring off the tyres...."

[/ QUOTE ]
........and there was always a window open, sometimes two............

 

[TamarMike]

Great! .................... tomorrow I should be able to recognise fellow forumites as they are likely to be driving round and round a roundabout with a balloon bobbing around next to them /forums/images/graemlins/smile.gif

 

[Piers]

[ QUOTE ]
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?

 

[Csail]

So very basically an object lighter than air will to the opposite to something heavier?