# Can a water balloon thrown from a building kill someone?

How can I learn about from what height (if any) could an average-size water balloon kill (or injure?) a person? What forces would need to be taken into consideration?

Is it frozen?

I’ve seen a water balloon tossed from the 16th floor or so cave-in a car windshield. Probably wouldn’t have been too good if it had hit a person.

Killing and injuring are two very different things. You wouldnt need to be that high up in order to whip a water balloon at someone’s head and injure them. As far as killing them, dunno.

How might I calculate the exact force exerted by a water balloon on the body per story?

oh and** Darth Nader:** Not frozen.

People die sometimes just from a trip and fall… one blow to the noggin and a bad landing?

It would depend on the weight of the balloon. the size of the stories, maybe wind gust also.
try poison its easier lol

One important factor is the elasticity of the balloon. In most cases, I expect the balloon to deform round the skull, burst and transfer less energy to the target. Also, the balloon may deform due to air resistance as it falls, which could limit the terminal velocity.
Given the comment above re a car windshield - the flat surface does not allow the dispersal of energy round and past the impact, although it will be over a wider area - this could break the windshield.

So, we eventually determine the exact height which maximizes the likelihood a water-filled balloon will kill someone. Later today I read a breaking news story about a man killed by a water balloon dropped from that height. Coincidence?:eek:

When I was an undergrad, a group of guys on my floor in the dorm constructed a slingshot from the bole of a small tree and about 20 feet of surgical rubber tubing, with a washcloth at the midpoint for holding the load. They shot water balloons with it, and could throw them the length of a city block (without the balloon breaking upon launch).

One day they launched it at a dorm window across the courtyard, a mere 20 feet or so away. Thwe balloon punched a perfectly round hole through the glass, kind of like the way cartoon characters going through glass sometimes leave a perfect outline of themselves instead of shattering it.

That’s a pretty impressive concentration of force and momentum. I can’t help but think that a person on the receiving end of that would sustain an injury. If you hit them just right, maybe you could kill them.

Disregarding the material of the balloon itself, you can calculate the pressure of impact based on the water’s speed and density. The speed can be calculated from the height of the drop. The total force of impact can be calculated based on pressure and contact area. The size of the balloon will affect both the contact area and the duration of the impact, but it won’t really affect the pressure (unless the balloon material is extremely strong).

IMHO, a large balloon dropped from more than a few feet can cause serious injury. As evidence, consider this balloon dropped from four stories onto a porta-potty. Imagine you’re walking by when that hits your head. It won’t cave your skull in directly, but it may break your neck and/or knock your head violently to the pavement - which would cave your skull in.

Clearly that’s not an “average” sized water balloon, but you can see the potential for grievous injury even from smaller ones.

Just reverse the question - “From how high would you like to fall into still water?” (No diving or toes first)

The surface area impacted might be less with a water balloon, but the pain becomes more personal…

Not the same at all. Skydivers learn that hitting water at terminal velocity is essentially the same as hitting solid ground, whereas a water balloon has relatively small momentum relative to a falling person and a tendency to deform and likely burst on impact, so if it hits a smallish object it will tend to shed much of its momentum around the object’s perimeter. Not to say that it’s not potentially dangerous, but not the same thing at all as falling into water.

Assuming a water balloon holds a half a liter of water and is roughly spherical (and that I did my math right), at sea level the terminal velocity given by this calculator is about 93 m/s.

The actual terminal velocity of a balloon is going to be less than that since the balloon will deform from a sphere and have a larger cross-sectional area.

Doing a bit of handwaving, that speed would be reached after ~11 seconds of falling, which implies a height of ~600m.

So, if you can’t kill someone from the Tokyo Sky Tree, it’s not going to help to climb up the Burj Khalifa.

From personal experience as a 12-year old boy (52 years ago,) I can tell you that a well-thrown water balloon imparts most of its force before bursting. It really hurts. Consider that a pint of water weighs a wee bit more than a pound. Throwing a balloon bigger than a pint is likely to drench the thrower, not the target.

Dropping a bigger balloon, though, shouldn’t be a problem. Now, if you wanted to make a more harmful water balloon, I’d suggest using a bigger balloon. Putting, say, a gallon of water in a balloon that would hold much more would deliver more of the force before bursting.

If mayhem is your goal, though, why not use a jug? Or an anvil? Maybe a piano!

It’s always darkest just before the piano lands on you. --Oliver Faltz

Years ago, I visited some friends in a college dorm. This being an all-girls school, the girls on the second floor would climb out their windows onto the roof of the first floor to sunbathe, often in the nude, since no men were around or allowed in the dorms. (I was sneaked by some girls)

One of the girls had the great idea of dropping water balloons on the sunbathing girls below, from the 5th floor. We filled the sink with maybe 20 balloons, and started pitching them out the window without looking.

The screams just made it funnier, until we realized they didn’t sound fun. Turns out the roof is covered in gravel, and when the balloons hit, they sprayed the rocks like shrapnel.:eek:
Clearly this was a practice we did not repeat. I would not have wanted to be down there during such an attack!

Did the hardass Dean give you a chewing out and threaten to expel your fraternity from the dance-off?

At 93 m/s, 500 grams of water had the energy of 2 162 joules. That’s about the same as a 5.56 mm rifle bullet.

The thing is, the energy is spread over enormously more surface area - instead of a tiny bullet tip, it is diffused over half a liter of water. Given a person can survive being shot in the head while wearing a helmet (which spreads out the energy), I think the balloon impact is survivable.

I don’t think this quite works. Up until very recently nobody wearing a helmet would survive being shot in the head by a 5.56 rifle. Not unless the bullet has travelled a long way and lost most of its speed. At 93m/s the bullet will not be stopped. Only the new Enhanced Combat Helmet is rated to stop a rifle bullet, all the existing helmet designs are only good for stopping fragments. Until there is some real experience with people being hit, I would be very loath to suggest that such an impact is injury or mortality free.

The other problem with dropped water balloons has been noted earlier. They can produce compression damage at the top of the spine. In this case it doesn’t matter what area the balloon spreads over, as the damage is not at the point of impact, but where the force is concentrated in the body. In this case we need an estimate of the peak force rather than the energy.

UC Davis circa 1980?