Because it is highly flammable.
'Hot air' balloons don't use hydrogen. They use hot air. Balloons that use hydrogen are not referred to as 'hot air' balloons. The only balloons that can accurately be referred to as 'hot air' balloons are the members of the balloon population that derive their lift/buoyancy from the presence of hot air. Of course, if a balloon used no hot air, then it could freely be referred to as a 'hydrogen' balloon, a 'helium' balloon, a 'water' balloon, etc., depending in congruent harmony with the nature of whatever substance had been chosen with which to inflate it it in order to maintain its fulsome shape.
A hydrogen balloon rises in air because the hydrogen gas inside the balloon is lighter than the surrounding air. This makes it buoyant, causing it to float upwards. The difference in density between the hydrogen gas and the air creates an upward force, lifting the balloon off the ground.
Hydrogen is dangerous for use in balloons because it is highly flammable and can easily ignite in the presence of oxygen. If a spark or flame were to come into contact with the hydrogen gas inside the balloon, it could cause an explosion. This poses a significant safety risk to both the balloon and anyone nearby.
The hydrogen in a sealed rubber party balloon is compressed slightly by the balloon rubber. So its density decreases a little, its pressure increases, and its temperature increases. But the temperature soon returns to the ambient temperature as heat is lost through the balloon wall. Also, the hydrogen will not stay in the balloon for long because it will leak out through pores in the rubber.
hot air balloon.
There is the weather balloon, and the zeppelin. Both use Helium, and no longer Hydrogen due to hydrogen's tendency to quickly catch fire.
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The first balloon filled with hydrogen was launched in August 1783.
'Hot air' balloons don't use hydrogen. They use hot air. Balloons that use hydrogen are not referred to as 'hot air' balloons. The only balloons that can accurately be referred to as 'hot air' balloons are the members of the balloon population that derive their lift/buoyancy from the presence of hot air. Of course, if a balloon used no hot air, then it could freely be referred to as a 'hydrogen' balloon, a 'helium' balloon, a 'water' balloon, etc., depending in congruent harmony with the nature of whatever substance had been chosen with which to inflate it it in order to maintain its fulsome shape.
in a balloon and in a hydrogen car
A hydrogen balloon rises in air because the hydrogen gas inside the balloon is lighter than the surrounding air. This makes it buoyant, causing it to float upwards. The difference in density between the hydrogen gas and the air creates an upward force, lifting the balloon off the ground.
hot air balloon
A hot air balloon doesn't contain helium or hydrogen.
A balloon with CO2 instead of helium or hydrogen
Hydrogen is dangerous for use in balloons because it is highly flammable and can easily ignite in the presence of oxygen. If a spark or flame were to come into contact with the hydrogen gas inside the balloon, it could cause an explosion. This poses a significant safety risk to both the balloon and anyone nearby.
The hydrogen in a sealed rubber party balloon is compressed slightly by the balloon rubber. So its density decreases a little, its pressure increases, and its temperature increases. But the temperature soon returns to the ambient temperature as heat is lost through the balloon wall. Also, the hydrogen will not stay in the balloon for long because it will leak out through pores in the rubber.
hot air balloon.