Surprisingly, if you’ve ever had this experience you might have noticed that the balloons move backwards — just the opposite of your body. Why? It’s because the balloons are floating in the air that fills the car. The air itself is subject to the same acceleration as your body. When you hit the brakes, the air continues moving forward the same way you do. More air gets pushed to the front than remains in the back. So there is momentarily greater air pressure at the front of the car. The floating balloons register this by being pushed backwards. You can try this with a candle inside a glass container. Push the container forward and then stop. The flame will tilt backward! The air inside has been accelerated so that it briefly crowds one end of the container, forcing the candle flame back toward the area of lower pressure.