### Instruction: What causes that feeling of weightlessness when you're on a rollercoaster?
### Response: The feeling of weightlessness when you’re on a rollercoaster is caused by negative gravitational force, also known as g-force. Negative g-force occurs when you accelerate downwards, and is commonly felt in roller coaster elements like camelback hills, which are hump-shaped hills that travel straight up and down. Elements like these are designed to lift riders out of their seats, giving that feeling of weightlessness.