If you take a helium-filled balloon in a car it will float against the car roof. What will the balloon do if.?
598306
nothing-\nthe system of atoms inside your car is stationary relative to the baloon.
53886
Since the air inside the balloon is heated, the molucules are more active and therefore spread out. The weight of the air inside the ballon is less than the weight of the air that the ballon displaces.
1864
It would definitely depend on the gas used. Some gases are heavier than air and would fall istead of rise. Consider also the pressure inside the ballon. It may rupture with the decrease in atmospheric pressure.\nToo many variables to give you a proper answer.
388915
As the air pressure decreases around it, the air, if contained in a flexible enclosure, would expand, pushing the sides of the container outward. IE: a balloon getting bigger. But I'm not sure what you mean by a "parcel" of air.
420827
high density - at least compared to air. this is why anything sinks in a fluid; rocks are higher in density than water or air so they sink, helium balloons are lower density than air so they float.
10432
The balloon is filled with hot air by the burner.  The hot air inside the balloon rises because it is lighter than cold (or cooler air).  assuming you mean't a hot air balloon.\n\nNobody is sure about helium ballons because we always suck the helium out so we can talk weird.
475777
All gases get denser as they cool. Air in a balloon would also deflate if it gets cold. The gas in the balloon would expand if the balloon got hot.  Not to get too complicated, but colder temperatures make the molecules of the gas get closer together, which makes the balloon shrink.
404977
Hahahahahahaha, how amusing the previous anwers are.\n\nThe balloon would continue to rise in the atmosphere until it reached a height where the pressure inside the balloon was equal to the pressure outside the balloon...then it would remain at the same height, moving in the wind, maybe slightly up and down due to thermals...until it burst !
618509
fill water balloons with different amounts of water and drop them at the same height to see if they fall differently.  =)
686605
Helium is lighter than air and cause the ball to float away.\n\nCarbon Dioxide is heavier than air so the ball would not bounce so well and it would be harder to kick.\n\nOxygen is lighter than air, but the difference is so small you wouldn't notice, no more that a ball being slightly over/under inflated.\n\nSince air is the cheapest, at a cost of nil, I suggest you put that in you balls.
881994
An balloon has positive buoyancy (floats) if the volume of air it displaces weighs more than the balloon. This is the same as saying the balloon is less dense than the air it is in.\n\nIn air, which is mostly nitrogen and only about twenty percent oxygen, a balloon will not float if its overall density is greater than air. That is, if the balloon and the gas it contains weighs more than the volume of air that it occupies the balloon will sink. So you can't fill the ball on with air and expect it to float because the balloon fabric is denser than air.\n\nHowever, there are three (and only three) gases whose densities are less than air: hydrogen, helium, and hot air. If the volume of the balloon is large enough, the weight of the hydrogen or helium or hot air when added to the weight of the fabric will be less than the weight of the air the balloon displaces. The balloon rises.\n\nAll of this is commonly referred to as manifestations of Archimedes' Principle.
946246
Helium particles are very small, in fact they are the smallest free particles that normally exist in nature. Although the plastic your balloon is made out of can stop water and sand and marbles and various other materials that have large particles, helium is small enough to go through, so it leaks.\n\nNow, there are certain kinds of balloons which are made out of special plastics and leak hardly any helium at all. However they are more expensive than the standard, cheap, leaky ones.
1026998
nothing will happen to him.  the only way something may happen is if lightining stricks the car itself
958394
You could tie a long string or ribbon on it and let it go.  At some point, the balloon will stop rising.  Cut the string just where it touches the floor.  Neutral bouyancy achieved!
315960
Properties of Gases \n\n1.  Indefinite shape -- you can squash an air-filled  balloon to make circus animals\n2.  May expand -- balloons get bigger when temperature gets warmer\n3.  May compress -- can put lots of air into a car tire\n4.  Have low densities -- balloons filled with air will float on water\n5.  Diffuse uniformly -- put a pizza on the front seat of the car and the people in the back seat get hungry pretty quickly -- that pizza vapors travel to fill the car! \n\n11.2  Atmospheric Pressure \n\nEven though we can't see the air around us, we know it's there and those molecules bouncing around exert a force on our bodies.  Fortunately, the force is the same on all sides of us, so it equalizes out and we don't notice that we're pushing against the air as we move our bodies. \n\nWe use a barometer to measure pressure.  We can use lots of different units depending on the system we're using.  Normal atmospheric pressure at sea level is defined as "1 atmosphere of pressure";  we call this by the special name "standard pressure".  The equivalent measures in other  units for standard pressure are given in table 11.1;  when we talk about standard pressure in this course we will use units of atmospheres, mm Hg and torr.  You're probably familiar with the weatherperson talking about pressure in inches of Hg.  If you use 2.54 cm = 1 inch, you can do the conversion from inches of Hg to cm and then on to mm of Hg.  There's no magic here, it's just a metric/English conversion example. \n\nYou may be curious about how a barometer works.  Here's my interpretation.... \n\nLet's start with the diagram on page 295 which is a representation for the workings of a barometer. It helps to talk about how this setup is put together. One would hold the tube "right side up", that is, like a test tube and fill it "to the brim" with mercury. One then inverts the tube in a pool of mercury (taking appropriate safety precautions). Immediately some of the mercury will flow out of the tube. How much flows out depends on how much pressure the atmosphere exerts on the pool of mercury. If the atmospheric pressure is higher, there is more pressure on the pool of mercury and the material in the tube stays at a higher level. If the atmospheric pressure is lower on a given day, more mercury is allowed to flow out of the tube. If the atmospheric pressure increases again, more mercury is pushed pack up into the tube. It is important to recognize that a virtual vacuum (except for a few stray mercury molecules) exists above the liquid in the tube which exerts no pressure (has no influence) on the height of the material in the tube. The only influence on the height of the material, is the air pressure on the puddle of mercury at the bottom.\n\nThe number the weatherperson gives is the height of the column measured in inches or mm (of mercury). We use mercury because it is so dense. If we were to use a water column instead (mercury is 13+ times as dense as water), the column would have to be 13+ times as high.  \n\n  Do example exercise  11.1 and the self test.  You can make up unit factors using any pair of these units to do homework exercises 5 and 7. \n\n11.3  Variables affecting Gas Pressure \n\nThink of gas pressure as the effect of molecules hitting the walls of a container.  When the molecules hit harder, the pressure is increased.  The tire pressure in your car can be affected by 3 things:\n \n  \n\nVariable What we measure Predicted effect on pressure of the gas Why? Also true (follows logically); complete with increase or decrease \nvolume of the container how much air the tire can contain increase volume, decrease pressure more space for the molecules to move around, so don't hit walls of container so hard decrease pressure, (       ) volume \ntemperature of the gas temperature of the air in the tire increase temperature, increase pressure molecules moving faster, so hit
751261
It will accelerate rapidly to the surface of the water, and then continue to float upwards through the air, but with less acceleration.  This is all due to the buoyant force.  When an object is immersed in a fluid, the fluid exerts an upwards force equal to the weight of the displaced fluid.  Of course, gravity still acts downwards on the object.  But if the object is placed such that it displaces a volume of fluid with a greater weight than itself, as when the object is hollow or is less dense than the fluid, the net force is upwards.  Helium is less dense than air, and is much less dense than water.  Since water is more dense than air, the displaced volume of water weighs more than the displaced volume of air, so the buoyant force of the water is greater than that of the air.  But it is always a net upwards force, so the balloon is always accelerating, until it reaches its terminal velocity.  Terminal velocity is usually encountered with falling objects, but would also occur in an object accelerating upwards.
536322
a tv program showed that approximately 2600 balloons filled with helium is needed to lift 20 kg child a few centimeters of the ground. (if i remember right, of course)