When you have a balloon floating in a car and start driving, instead of getting thrown back, it actually flies forward. What? Are balloons immune to inertia? Is physics broken? Nope. As SmarterEveryDay explains, it actually makes perfect sense, as science always does.
Balloons aren't weirdly above being affected by the first law of motion, but because they're lighter than air (when filled with helium), it just affects them differently. When you put the pedal to the metal in your (awesome) minivan, what really happens is that all the air sloshes to the back like the fluid it is, and the balloon floats to the "top," the pocket near the driver where there's less air.
It's a cool but in hindsight totally obvious little quirk of physics, one that can make science feel as magical as it did when you were five years old. [SmarterEveryDay]