It stops you from slamming your head when you have a car crash.
The bag fills up with air very quickly after sensors in the hood
detect that there has been a crash
What fills a helium balloon?
Helium which is a lighter-than-air gas, allowing the balloon to
float upwards.
Does light fill more space in a vacuum or in air?
In air, light reflects off gas molecules and hence, "fills more
space".