You’re driving along on your way to deliver some helium balloons to a birthday party. Suddenly you hit the brakes. As your car rapidly decelerates, you feel yourself pushed up against the seatbelt. Why? That one’s probably not too tough. Although you may think you are sitting still when driving, your body is moving forward at the same speed as the car itself. So, when you hit the brake the car slows down but your body is still trying to go forward. You experience a sensation something like being pressed against the front of the car. The next question is a little trickier. Which direction did the balloons move? Think for a second. The car is going forward and abruptly stops. Which direction do the balloons go?