Rapidity

Rapidity is a way we describe how fast something is moving. It's kind of like a race where we want to know who is going the fastest.

To understand rapidity, imagine you and your friend are both riding bikes. You start at the same spot and race to a finish line. You both pedal really fast, but your friend is going a little faster than you. So even though you're both going fast, your friend is winning the race because they're moving at a higher rapidity.

Now, let's say you continue to ride your bike but your friend gets in a car and starts racing alongside you. Even though you're both still moving fast, your friend's car is moving much faster than your bike. In this case, your friend has a much higher rapidity because they're moving much faster than you.

Rapidity is a measurement that helps us compare how fast things are moving, no matter what type of vehicle or situation we're in. It's like a special "speedometer" that helps us understand who's moving faster and by how much.