💭 The Question
Today, I was asked in a group I’m part of:
“How can a meteor hit Earth many times faster than terminal velocity?”
It’s a great question — and the answer shows how space physics, air pressure, and Newton’s laws all work together.
🚀 Terminal Velocity Explained
Terminal velocity happens when the downward force of gravity is exactly equal and opposite to the force of air pressure.
This causes the opposite forces to balance out, so acceleration stops.
📘 Newton’s First Law of Motion says:
“An object in motion will remain in motion at a constant velocity unless acted upon by a net external force.”
When forces are balanced, the net force = 0, and by Newton’s Second Law (F = ma), acceleration stops (a = 0).
That constant speed is the terminal velocity.
☁️ Why Smaller Meteors Slow Down
- Smaller meteors have more surface area for their mass, so air pressure quickly cancels gravity.
- They reach terminal velocity, often around 100 mph — about as fast as a baseball pitch!
- Most small meteors burn up before ever reaching the ground.
🪨 Why Big Meteors Stay Fast
- Large meteors have far less surface area per unit of mass, so there’s less air pressure to slow them down.
- They have enormous momentum (mass × velocity) and keep going.
- Even the atmosphere can’t balance the forces before they hit Earth — so they never reach terminal velocity.
🌌 Cosmic Starting Speeds
Both small and large asteroids enter Earth’s atmosphere already moving at 20–70 km/s — or 20–70 times the speed of sound.
They’re not accelerating from rest — they’re already traveling at orbital speeds when they hit our air.
💥 Real-World Example: Chicxulub Impact
66 million years ago, a 10-km asteroid struck near Chicxulub, Mexico.
- Speed: ~20 km/s (12 mi/s) — 58× the speed of sound
- Energy: 4.5 billion Hiroshima bombs
- Result: global fires, tsunamis, a dust-filled sky, and yes — the end of the dinosaurs.
⚡ Key Takeaways
✅ Terminal velocity = air pressure balances gravity → no more acceleration
✅ Small meteors slow down easily (high surface area : mass)
✅ Big meteors barely slow at all (low surface area : mass, huge momentum)
✅ Meteors start fast in space — that’s why they hit many times faster than terminal velocity
