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 Post subject: Re: riddle(OQ)
Unread postPosted: Wed Jan 02, 2013 6:19 pm 
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A helium filled balloon is much lighter then our bodies. So when a car accelerates, our body tends to move backwards and the much lighter balloon will move forward the same as the car :hmz:
:) Would you like more :)

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 Post subject: Re: riddle(OQ)
Unread postPosted: Thu Jan 03, 2013 6:20 am 
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Please clarify a little more for me, Philip, if you will: do you mean that the balloon will move backwards, forwards, or stand still, within the car, but relative to it, as it accelerates?

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 Post subject: Re: riddle(OQ)
Unread postPosted: Thu Jan 03, 2013 6:34 am 
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The same direction as the car = forward, moving away from the centre, towards the windscreen. (Gravity and air pressure)

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 Post subject: Re: riddle(OQ)
Unread postPosted: Thu Jan 03, 2013 8:09 am 
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Rooies, nice try; however, because the surrounding air is heavier than the helium balloon, as the car accelerates, the air will move towards the back, pushing the balloon forwards towards the windscreen! Strange, but true. :thumbs_up: Well done, Philip. :clap: :clap:

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 Post subject: Re: riddle(OQ)
Unread postPosted: Thu Jan 03, 2013 9:02 am 
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Like the Kudu horn system, I guess I have now earned my fifth Krokodil and thereby became a legendary Krokodil. I think I should stay with Good Morning, Good Afternoon.... That one I can't get wrong. :doh: :D Or better still, join the :thumbs_up: :D brigade

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 Post subject: Re: riddle(OQ)
Unread postPosted: Thu Jan 03, 2013 9:22 am 
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Rooies, how can you win the Lotto if you never try! :twisted: Always love your participation on the quizzes, and elsewhere on the forum; so don't you dare disappear! :wink:

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 Post subject: Re: riddle(OQ)
Unread postPosted: Thu Jan 03, 2013 11:21 am 
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OWN, I have trust in your superior knowledge but something is worrying me. You say that the air in the vehicle will move backwards because it is heavier than helium. Now if your theory is correct than the lighter helium will push the heavier air in front of the balloon out of its way to move to the front of the vehicle. The balloon will have to overcome the resistance of the heavier air. This doesn't seem correct. If you put a light ball in the center of a bucket of water inside the car, should the ball then move towards the side of the bucket, if the vehicle moves? If you throw a light stick in a stream of water, it will go with the flow but a heavy stone will sink.

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 Post subject: Re: riddle(OQ)
Unread postPosted: Sat Jan 05, 2013 2:26 am 
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Rooies, the way I understand it is that, as the vehicle moves sharply forward, the air in the car will flow backwards, creating a relative and partial vacuum towards the front of the vehicle, and hence in front of the balloon. Less impeded by the denser air that was in front before the car moved, the balloon will now slide forward into the vacuum.

As to your analogy with a ball in a bucket of water, I think that, as the car moves forward, the water and ball will (hopefully) remain in the bucket and so gain momentum. When the car slows down, the water and ball will continue to move forwards; the water will be stopped by the bucket surface, allowing the ball - which has less resistance being on the surface of the water - to move forward against the front of the bucket.

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 Post subject: Re: riddle(OQ)
Unread postPosted: Sat Jan 05, 2013 8:31 am 
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@ OWN. The way I see it is that the air in front of the balloon will follow the path of least resistance when moving backwards, and therefor directly to the back. In the process of moving backwards, it surely will take a lighter object with it. IMHO, when the heavier air is pressed against the back, the balloon will 'pop' out and then move forward, when the 'compressed' air starts to even out after acceleration.

Very good question :clap: :clap: More please

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 Post subject: Re: riddle(OQ)
Unread postPosted: Sat Jan 05, 2013 8:37 am 
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Rooies, now that I think about it, it is a possibility that the initial backwards movement of air may indeed dislodge the balloon for a moment, but then the partial vacuum will be rapidly created and the light balloon should move promptly into the low pressure area. Also, I wonder if the upward push of the helium on the balloon wouldn't rather keep the balloon against the car's ceiling? Two things are required to happen here to resolve this for good: (i) we must invite a physicist to come on here and clarify (do you know any good ones?); and (ii) we need to actually try it out with a real helium balloon and a real car - anyone volunteering? :hmz:

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 Post subject: Re: riddle(OQ)
Unread postPosted: Sat Jan 05, 2013 8:51 am 
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Good suggestion OWN. We can have our own 'mythbuster' team. :thumbs_up:

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 Post subject: Re: riddle(OQ)
Unread postPosted: Sat Jan 05, 2013 8:56 am 
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:lol: :lol: :thumbs_up:

Maybe we could start by testing out a hotel's validity in Kruger? :hmz:

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 Post subject: Re: riddl e(OQ)
Unread postPosted: Sat Jan 05, 2013 11:29 am 
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Actually guys , the baloon does not " move backwards " .
In terms of Boyle's law , all the gas/air , inside the vehicle will exert equal pressure in all directions , and will be of equal pressure everywhere within the motorcar - except of course within the baloon , which is filled with a different gas ( Helium ) , and as such have a different pressure within the baloon . Then , the baloon itself has a different mass from that of the two different gases ( the air in the vehicle , and the helium ) .
While the vehicle is standing still , of course the baloon-filled gas is also in a state of inertia , therefore , when the vehicle starts moving forward , any mass that is not fixed or attached to the vehicle , will continue to remain in a state of inertia , unless some form of force/energy is exerted on it . In this case , the moving air within the vehicle will exert sufficient force on baloon in order for it to start moving forward with the rest of the vehicle and its contents .

To sum up , initially the baloon will remain still for a fraction of time , and then it will go forward . But it will remain in the same position relative to the rest of the vehicle , until the vehicle comes to a stand-still , at which time it should continue moving before coming to a standstill in exactly the same position as previously .ie before the vehicle statrted moving .

Q.E.D.

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 Post subject: Re: riddle(OQ)
Unread postPosted: Sun Jan 06, 2013 9:03 am 
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:hmz: Quod erat demonstrandum? Nice spin on the problem at hand, Okie, but a little question please, if you will ... if the balloon continues moving forward when the vehicle stops, how does the balloon land up in the same position it was when the car began accelerating?

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 Post subject: Re: riddle(OQ)
Unread postPosted: Sun Jan 06, 2013 5:26 pm 
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Hi all, have a look at this:
Quote:
Short Answer: The balloon does the opposite to whatever your body would do. Thus, if the car comes to rest the balloon moves towards the back. The key is that the balloon is filled with helium (He) and you are made up of stuff much heavier than air.
Suppose you had the balloon filled with He and tied to the floor of your car, perhaps, around your hand brake and your car is at stopped. If you then 'hammer the gas pedal' you will be pushed back in to your seat whereas the balloon will go forward! Turn left, the balloon goes right. Turn right the balloon goes left, and stop - the balloon goes back.
It has to do with the motion of the air in your car. When you are at rest and then go forward all of the air rushes to the back of the car and you have created an area in the back of your car of higher air pressure. Since He is lighter than air it wants to 'float' away from that area and moves forward.
Answered by: Peter Feeney, B.S., HS Physics Teacher



The movement of a helium-filled balloon is the result of a difference in the density of the surrounding air. Since on Earth, the air density is higher the lower you are in the atmosphere due to the weight of the air itself, the force per square inch (pressure) it exerts on the balloon is less at the top of the balloon that it is at the bottom, resulting in an unbalanced force called thebuoyantt force. If this buoyant force is greater than the weight of an object, as is the case for a helium-filledballoonn, the object will rise in the air, moving toward the airwithh a lower density.
When a car stops suddenly, the air inside the car continues to move forward a little longer than the car itself, due to the tendancy of an object to maintain its motion until a force acts on it (inertia). The air is stopped by the front of the car's interior and tends to 'pile up' there. As a result, the air in the front of the car becomes slightly more dense than the air in the rear of the car, creating more pressure on the front side of the balloon. This causes the balloon to move toward the rear of the car, where the air is less dense, just as the same balloon released outside will move upward, toward the less dense air.
Interestingly, a helium-filled balloon released on board an orbiting spacecraft will neither rise nor fall, since it is the weight of the air that creates the differences in air density here on the Earth. In free fall everything is falling at the same rate and is in a weightless state, so the air is of equal density everywhere on board the spacecraft.
Answered by: Andrew Franks, M.A., Physics Teacher, Lee High School, Midland, Texas

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