Why, in a thermal flask, does having a vacuum layer help keep the coffee warm?
Heat is transferred by 3 processes, conducation, convection and radiation. Having a vacuum layer stops heat being transferred away from the coffee by conduction. Conduction works by air molecules bumping into eachother and transferring some of the energy they have, therefore if you remove the air then you stop energy/heat being taken away in this way which helps keep the coffee warmer for longer.
BO
Related Physics GCSE answers
All answers ▸A car's speed changes from 10m\s to 40m\s in 10 seconds. What is its acceleration?
Can you explain the difference between a real and a virtual image?
What can the nucleus emit during radioactive decay?
If fusing hydrogen nuclei together puts them into a lower energy state, and matter always wants to be in a lower energy state, then why hasn't all the hydrogen in the universe already done this?