The Inner Monologue

Ah, the classic “If two things hit each other at X kph, it’s like hitting a wall at X times two!” argument. A favorite of overconfident internet experts, sensationalist headlines, and people who definitely didn’t pay attention in physics class.

Let’s settle this once and for all before someone tries to argue that two cars crashing at 60 mph each is “just like hitting a wall at 120 mph!” (Spoiler: It’s not. It never was. Stop saying it.)

The Myth That Won’t Die:

• Two e-bikes collide head-on at 50 kph each? “That’s like hitting a wall at 100 kph!”
• A 40 kph bike smashes into a 60 kph bike? “That’s a 100 kph impact!”

The Reality? Nope. Not even close.

Here’s Why You’re Wrong (With Math This Time):

Forces in collisions don’t add like a bad action movie stunt. Instead, they follow the cold, unfeeling laws of vector math.

Case 1: Two 50 kph Collisions

• What people think: “50 + 50 = 100 kph impact!”
• What actually happens: The forces cancel out, and each bike experiences the equivalent of hitting a stationary wall at 50 kph.
• Why? Because momentum is conserved. The relative speed is 100 kph, but the impact force on each object is still just 50 kph worth of ouch.

Case 2: 40 kph vs. 60 kph Collision

• What people think: “40 + 60 = 100 kph disaster!”
• What actually happens: The average speed is (40 + 60) ÷ 2 = 50 kph, so each bike feels the same force as hitting a wall at 50 kph.
• Why? Because the faster bike (60 kph) effectively “loses” 10 kph, and the slower one (40 kph) “gains” 10 kph. Net result? Same 50 kph impact.

The Brick Wall Test (Because You Still Don’t Believe Me):

• If you hit a stationary wall at 50 kph, the wall doesn’t hit back.
• If another bike hits you at 50 kph, it does hit back—but the force you feel is still 50 kph, not double.
• If a 60 kph bike hits a 40 kph bike, the forces balance out to… you guessed it… 50 kph.

Why Do People Keep Getting This Wrong?

1. Drama sells. “Double the speed!” sounds scarier than “It’s just the average, actually.”
2. Bad intuition. Humans think in simple addition, but physics laughs at simple addition.
3. Misleading analogies. Movies and clickbait headlines love exaggerating collisions because “100 kph crash!” gets more clicks than “technically 50 kph, but still painful.”

Final Verdict:

• Two equal-speed crashes? The impact is the same as hitting a wall at that speed.
• Two different-speed crashes? The impact is the average of the two speeds.
• Any other interpretation? Wrong. Stop it.

TL;DR: Speeds don’t add in collisions. The average does. Vectors always win. Now go forth and correct someone (gently, because they’ll probably argue anyway).