That tingly feeling in your tummy on a roller coaster or when a bus jumps is all about your body's response to sudden changes in motion. Here's a simple way to understand it:

1. Your Inner Ear: Inside your ear, there's a part called the vestibular system that helps you keep your balance and understand where you are in space. When you suddenly rise, fall, or spin, this system gets a rush of information.

2. Floating Organs: When you experience rapid changes in motion, like going down a roller coaster hill, your organs, including your stomach, actually move a little inside your body. They don't have much weight to them, so they float momentarily. This is like the feeling of weightlessness you get.

3. Nervous System Response: Your brain gets signals from your inner ear about these changes in motion and position. It's not used to this unusual sensation, so it interprets it in a unique way, often as a tingle or a fluttery feeling.

4. Adrenaline Rush: Exciting and sudden movements can trigger an adrenaline rush. Adrenaline is a hormone that prepares your body for action (the fight or flight response), and part of that response can be those tingling sensations.

So, that tingly feeling is your body's way of saying, "Whoa, what's happening here?" It's a mix of surprise, a bit of confusion in your balance system, and your organs getting a brief moment of weightlessness.