Why does a rocket have to go 25,000 mph (about 40,000 kilometers per hour) to escape Earth? – Bo H., age 10, Durham, New Hampshire There’s a reason why a rocket has to go so fast to escape Earth.

There’s a reason why a rocket has to go so fast to escape Earth ... the amount of propellant needed would make the rocket too heavy to get off the ground. So what happens when the propellant ...