Destin, from Smarter Every Day, did a great experiment which baffled me. For a while I would now know what the heck is happening in there and then he showed the example with the water in the jar where you would also see a bubble of air. When you accelerate that jar forwards, the water rushes towards the end of the jar and the air bubbles are pushed forward. Ingenious.
The same experiment was done in Destin’s car with a helium balloon tied to the floor. Whenever he accelerates in a given direction, the air in the car is pushed in the opposite direction and the balloon is pushed in the same direction he first accelerated. If you accelerate forwards, the balloons will move forward. Just crazy!