PROBLEM: What keeps a hot-air balloon in the air

Kids Science: Flying Tea Bag Hot Air Balloon | TinkerLab

You are probably well aware that when you compress air quickly in a bicycle pump the pump gets hot quickly. The energy imparted by your muscles is transferred into heating the gas inside the pump and increasing the molecules' internal energy. This is the same reason spacecraft get hot when they re-enter the Earth's atmosphere - adiabatic compression (not friction). Diesel engines rely on adiabatic heating during their compression stroke to elevate the temperature sufficiently to ignite the fuel. If you had access to a temperature probe and a datalogger you could mount the probe into a screw fitting and screw it into the end of a pump. Let some masses compress the gas and take a few readings. It's up to you what data to take and how to work out how much mechanical energy is imparted to the gas by the falling masses. Is it okay to assume that there is such little time for heat to escape to the surroundings that Q (lost) = 0? Will the formula W = Fs be okay? has done a lot of the hard work for you.

Which Material Is Best For Hot Air Balloons: Nylon ..

You would have seen how gases expand when they are heated. Your teacher may have heated a flask with a balloon on the top to show it expanding; you may have seen a balloon shrink when dipped in liquid nitrogen at -198°C; and it is the principle behind how hot air balloons work. In class you would have called the law describing the relationship between temperature and volume Charles's Law or perhaps Amonton's Law (V ∝ T, when T is in kelvin and P and n are kept constant). There could be a great EEI in revisiting this relationship. There is no point in just verifying it as this has been done a million times. What you want to do is to extend the investigation of this law to look at the impact of changing variables and to consider allowing for errors.

Physics teacher at Urangan State High School, Hervey Bay, Queensland - Alan Whyborn - has his students investigate hot air balloons and the conditions needed for the balloons to catch fire. He said that he once saw a colleague in Canberra make hot air balloons from shopping bags, using metho and cotton wool, simply wired across the handles of the bag. They took them outside (on a still day), lit the metho and off they flew. On a number of the bags the opening collapsed in a little and the bags caught alight. He was horrified at the sight of flaming balloons releasing drips of burning plastic as they drifted casually through the air! He says: "In August 2007 in Canada, a fire broke out in a hot air balloon. Two people were killed. Could it be that the air in such a balloon may become excessively hot and cause the material of the balloon (the "envelope") to ignite and burn?" This sounds like the basis for an EEI: factors influencing the ascent of a hot air balloon.

What Did the First Hot Air Balloon …

Unless or until the US can start experiencing GDP growth greater than debt growth, the US appears to be stuck in a hot air balloon economy. With the debt ceiling around the corner, we may shortly test the hypothesis of whether or not the US is on a self-sustaining recovery path.

How does a hot air balloon float - 825749 ..

Once aloft, the balloon keeps rising with less fuel required than take-off. In this phase, loft is achieved with minimal fuel, or said differently, income (loft) is growing faster than debt (fuel). But, once the hot air balloon reaches a certain altitude where the air is thinner, further heights become more difficult to realize. The pilot needs to start burning more fuel (debt) if he intends to keep climbing (growth). At this point a marginal diminishing return sets in where the amount of incremental fuel (debt) required to keeping rising (income) becomes greater and greater. There is a point reached where no amount of incremental fuel can lift the hot air balloon any higher.

If the hot air is contained as it is in a balloon, ..

The more air you add to a balloon, the bigger it gets. Unfortunately this example doesnot test Avogadro's hypothesis that equal volumes of different gasescontain the same number of particles. The best way to probe the validity of thishypothesis is to measure the number of molecules in a given volume of different gases,which can be done with the apparatus shown in the figure below.

A person flying in a hot air balloon realizes he is lost

Inflated party balloons fall slowly to the ground because of their large cross-section for their weight (low density). Students often think a good EEI would be to investigate the effect of air resistance on falling objects (eg tennis, ping pong and cricket balls) but mostly the objects fall too fast and the measurement error is too great. A great EEI would be to suspend a motion sensor (ie a sonic ranger) from the ceiling and let an inflated balloon fall from underneath it. You could increase the mass (add paperclips etc) and redo the measurements keeping diameter constant. Then you could keep the mass constant and change the .... (you work it out!). The main things to look for are large lightweight objects such as party balloons (recommended if you don't have a sonic ranger), plastic soccer balls, inflatable beach balls, styrofoam balls (eg the round foam fishing floats in the photo below). Small weights can be taped on the bottom or pushed into the foam; and you may need quite a large fall height.

The simplest experiment would be to look at the effect of these variables on terminal velocity. If you want to look at the accelerating phase as well then you should read the caution below. For terminal velocity you just need to work out when the balloon has stopped accelerating. Usually it is after about 1.5 m of freefall but you would need to establish that. Most students put two horizontal rods (eg rulers) about 1 metre apart vertically and time the balloon's descent between these two markers. If you put another marker 1 m under the bottom one and timed the balloon through the second distance, the time should be the same if it is at constant velocity. The downward force (weight) is balanced by two upward forces: buoyancy and air resistance. I'd be looking up Reynolds Number (no apostrophe) and Stokes' Law (with apostrophe). Remember that air resistance varies with velocity (squared). And that why this is a tricky (but great) investigation for an EEI.