Thrust Structures

Today, Lucy, Hannah, and I worked with each other to create a "machine" that launches a plastic bottle up in the hair. First, we each created what we thought would work. After that, we tested our equipment. Lucy's creation worked the first few times, but them something went wrong afterwards. I tried mine, and it worked just fine. Next time, I would've have started with an idea rather than just jumping into something without thinking. That may have made my machine work even better.

Some Questions I have:
1. Why did Lucy's stop working after working so it worked so well at first?
2. Why do hot glue guns take so long to heat up?