Motorcycle helmets help make human Newton's Cradle
Surely you're aware of Newton's Cradle – named after famous physicist Sir Isaac Newton – even if you didn't actually know it was called Newton's Cradle. Click here for Wikipedia's page on the device... okay, got it? Good. So, it's that thing that people put on their desks at work with little metal balls suspended on very thin wires. Pull one side back, let go, and watch the other side act in response.