Now I know I promised that the unit on Materials was finally over; well, I guess I lied! Inadvertently, of course.....

It was perhaps Rekik who listened the most carefully on the day that I suggested we had 'crisp-eating' for homework.  He made it his personal goal to provided us with one empty crisp bag for each person in the class.  And 24 school-days later (yep, that's a bag of crisps each day!) he (with a bit of help from his friends) achieved his goal.

Which meant that today was the day we finally found out what material crisp bags are made of.  To begin with, we thought back to the 'sticky' problem Patricia had when trying to identify what material her sweet wrapper was made from (see an earlier post). 

Having thought carefully, Joe was confident that crisp bags are made from plastic.  Max agreed with him.  Tanmay wasn't so sure.  He suggested they might be made from paper; Matthew Duke thought this too.  And then Danah said they might be made from foil with Swati adding that foil is metal, and that she too thought they might be made from metal.

This time, the test we planned would involve the bags being put into a hot oven.  Evie told us that paper would burn in the oven.  Per thought that metal would melt, but when Fiona told us that her dad uses foil to cover potatoes when he cooks them in the oven, Per changed his mind; Joe said it would probably just get hot.  Rekik thought that plastic would melt.  We also found out that when plastic is made it is often stretched during the process and that if it is then heated afterwards, it 'relaxes' or shrinks to a 'more comfortable', smaller shape.

So group by group we went downstairs to the oven and put in a tray of crisp bags.  We crowded round the glass door (well, it was pretty exciting) and watched.....and before our very eyes, the crisp bags shrank - to less than half their original size.

Back in the classroom we did a quick survey.  What are crisp bags made from?  How many people think it's paper (a couple of uncertain hands raised; but lowered again when Evie reminds us that paper would 'get on fire' if it went in the oven).  How many think they are made from metal?  No hands raised.  From plastic?  A veritable forest of arms.

PS For anyone who cares about these things, this Blog was posted using Windows Live Writer.