How to apply heat on a balloon but not burst it...
As you all have noticed before, I like doing make and break things as a part of experimenting. However, this experiment was quite a disappointment since it did not involve any making/ breaking.
You will know what a convection current is from our previous experiment: Why Are Winters In Delhi So Polluted. A convection current is when cool air sinks, hence displacing the hot air and making it rise. So there is a circular flow of air. Now if we try to replicate the same thing with a balloon, it actually works:
Take a balloon and fill it with water. Then put it on top of an ignited candle. If you are doing not this for the first time, you will know that soot gets collected at the bottom of the balloon. Don't freak out if it gets on your hands- it will easily get washed off. The balloon does not burst. The water in the balloon absorbs the heat. There is a convection current set up in the balloon with the cold water continuously settling down and warm water rising, thus facilitating the boiling of water in the balloon. This is how campers can warm-up water in a paper bag
Another way to visualise a convection current is to put a drop of food colouring in a container with water, that is being heated. You can see the color rise up, as it gets carried up with the hot water. An alternative method is that you can take a cardboard box (approximately 6 inches * 6 inches * 2 inches), on one of the faces, cut a viewing window and seal it with a transparent plastic sheet. On the face opposite to this, stick black paper on the inside. Cut 2 holes on the top; these holes should be about 2cm in diameter and at a distance of about 5cm from each other). Place the box with the viewing window facing you. Now we need to slip in an ignited tea-candle and place it underneath the right hole. For this, you may need to have cut a re-closable flap on the side of the box.
Now you need to hold a burning incense stick (agarbatti- if you are looking for it at an Indian shop- it is commonly used in prayer ceremonies so it can be found more or less anywhere) over the left hole such that the smoke from the stick is being allowed to enter the hole.
What do you think will happen to the smoke?
Due to the burning candle, a convection current is in progress over the candle, and warm air is quickly being expelled out of the right hole. This takes the incense stick smoke also into its fold and the smoke is seen entering from the left hole and being directed quickly out of the right hole.
The set up takes some time to make but it's quite a visual treat to watch.
You will know what a convection current is from our previous experiment: Why Are Winters In Delhi So Polluted. A convection current is when cool air sinks, hence displacing the hot air and making it rise. So there is a circular flow of air. Now if we try to replicate the same thing with a balloon, it actually works:
Take a balloon and fill it with water. Then put it on top of an ignited candle. If you are doing not this for the first time, you will know that soot gets collected at the bottom of the balloon. Don't freak out if it gets on your hands- it will easily get washed off. The balloon does not burst. The water in the balloon absorbs the heat. There is a convection current set up in the balloon with the cold water continuously settling down and warm water rising, thus facilitating the boiling of water in the balloon. This is how campers can warm-up water in a paper bag
Another way to visualise a convection current is to put a drop of food colouring in a container with water, that is being heated. You can see the color rise up, as it gets carried up with the hot water. An alternative method is that you can take a cardboard box (approximately 6 inches * 6 inches * 2 inches), on one of the faces, cut a viewing window and seal it with a transparent plastic sheet. On the face opposite to this, stick black paper on the inside. Cut 2 holes on the top; these holes should be about 2cm in diameter and at a distance of about 5cm from each other). Place the box with the viewing window facing you. Now we need to slip in an ignited tea-candle and place it underneath the right hole. For this, you may need to have cut a re-closable flap on the side of the box.
Now you need to hold a burning incense stick (agarbatti- if you are looking for it at an Indian shop- it is commonly used in prayer ceremonies so it can be found more or less anywhere) over the left hole such that the smoke from the stick is being allowed to enter the hole.
What do you think will happen to the smoke?
Due to the burning candle, a convection current is in progress over the candle, and warm air is quickly being expelled out of the right hole. This takes the incense stick smoke also into its fold and the smoke is seen entering from the left hole and being directed quickly out of the right hole.
The set up takes some time to make but it's quite a visual treat to watch.
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