Why does a water balloon or paintball hurt so much if it doesn’t explode when it hits you?


Was wondering why this happens. I figured the ball exploding would hurt more.

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If you throw a rock at someone it doesn’t explode, but it hurts, right? A mass going at a given speed striking you is going to exert force on your body, and in the case of a paintball it does it over a relatively small area.

That hurts.

Initial energy from the impact is what breaks the paintball or water balloon. From there it disperses the rest of the energy in other ways over a larger area. When it doesn’t break all the momentum energy with no loss is transfered directly into you. And generally in a smaller area on your body.

Basic physics: Force equals mass times acceleration. A ball of a given mass, traveling a certain speed, will exert a certain amount of force when it strikes another object. If a paintball explodes on impact, some of the force is released outward from the point of impact (which is why there is always a bit of paint splatter), so less force is exerted directly to the flesh right at the point of impact. But if the paintball doesn’t explode, then all of the force is transferred directly into the flesh at the point of impact. Ouch!

The water balloon or paintball likely actually hurts more when it doesn’t explode, since exploding takes energy to tear the surface and send the water/paint flying in all directions – all the energy needed to do that means less energy being sent into you.

It’s a similar concept to cars: modern cars crumple when they get into an accident, which can look terrifying but all the damage absorbed into the car means less damage absorbed by the passengers inside. And if you’ve ever seen a person punch or karate chop a wooden board the same idea applies there too! Punching through a wooden board actually hurts less than punching the board without breaking it, since breaking the board means that energy from your punch is being absorbed and not all going right back into your fist.