Sunday, 14 May 2017

Explosive Science!

Which one of these bags do you think will make the biggest "BANG!!" when we pop them?

A supermarket bag, a snaplock bag and a paper bag...
We tested the snaplock bag first. We thought it was quite a 'tough' plastic and it was! Johnny had to stomp it with his foot to make it pop! It did make a loud bang...but was it the loudest? It didn't break the tough plastic - it popped along its 'zip'!

Next we tried the paper bag. Eva had a great go at popping it but it just wouldn't burst! I think we were all giggling too much by then! Mrs Sutherland had to help and...BANG! It burst through the bag with 2 really big rips! Was this one going to be the biggest bang?

Finally we got to the supermarket bag. Many of the D1 children thought it would be the loudest because it had the most air in they thought it would make the biggest bang. Zane used all his muscles...but it only whooshed the air out quietly through 2 tiny rips in the seam at the bottom of the bag. What???!!! 

So... which one was the winner? The paper bag was the loudest, then the snaplock bag and finally the supermarket bag. If you are allowed, try this again at home and see if you get the same results!

What makes the 'bang' noise? We did some investigating and found out that air is made up of molecules that push against everything they touch. This is called air pressure. A few of the D1 children talked about pressure when they were predicting what would happen - well done! Because we squeezed the air into our 3 bags,  the air pressure got bigger and when the bags popped, the high-pressure air rushed out! That change in pressure makes a shock wave that travels to our ears as a loud POP! The loudest pop comes from the highest air pressure...which was in the paper bag!

We had a really interesting question from Zane too. He said that we were blowing carbon dioxide into the bags and wondered if we would get the same if we used oxygen? Now that's an interesting idea to think about! 

One explosion down...many more to come!

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