ELI5 why aren't motorcycle helmets mandatory like seatbelts for cars?

ELI5: If trees get their carbon from CO₂ in the air, how can that same carbon end up forming huge amounts of solid material like wood, coal, diamonds, and the carbon in steel?

ELI5: How does the ground stay stable above oil drilling sites?

ELI5: Why does dirty air behind another Formula 1 car make overtaking so difficult?

ELI5: How does short term and long term memory work?

ELI5: When weather professionals say "it's __ degrees but feels like __ degrees"... isn't that subjective?

ELI5: How can a country have a huge economy but a relatively weak currency?