This one cost us nothing and was a big winner for my daughter, she even presented it at a state teacher's conference.
Which store brand plastic grocery bag supports the most weight without breaking?
We got new plastic grocery bags from several different stores, and we had a tension rod that we put in a doorway to her height so she could reach. You thread the bag handles over the bar, and then put weight in the bag-we used things such as a 5lb bag of sugar, cans of soup, any type of grocery item. When the bag broke, either the handles or the bottom, she weighed the bag on a good bathroom scale. She took pics of her performing the tests, and had both the broken and new samples of the bags tested, and put it up on a science display board with a report on how she tested and achieved her results. The results were interesting, she had fun doing it, it did not require a whole lot of time, and the report on the findings were fairly easy.
Hope this helps!