Anonymous
Anonymous asked in Science & MathematicsPhysics · 1 month ago

# Why do bullets not go far underwater, but spearguns can go 20 metres or more at high velocity ?

Update:

If a speargun used gunpowder, would the spear go ever farther underwater?

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• Anonymous
1 month ago

Lower  friction  coefficient

• Dixon
Lv 7
1 month ago

Bullets are just low in mass compared to a spear, so they slow down more quickly for a given opposing force from water resistance/friction. Also, at the initial high velocity of a bullet I think water presents itself as almost a solid because water does not flow out of the way at such speeds, so very quickly a bullet is reduced to a spear-like velocity, where its low mass then can't sustain its motion.

• 1 month ago

It's a matter of momentum, energy and resistance. A spear from a speargun masses a lot more than a bullet. As Aristotle showed, the terminal speed for an object is very much dependent on mass.

Even if the bullet is going faster than the speed of sound, it will slow down very quickly, mainly because the mass is so small. The spear has a lot of mass, so, even if it starts off at a comparatively small speed, it will go for far longer than the bullet.

spear with gunpowder propellant... probably, but it would take a lot of gunpowder to make the time to stopping much larger than the compressed air does.

• 1 month ago

Sound travels well in water though.

Whales communicate across hundreds or even thousands of miles when singing in a column of water with the correct salinity.

Edit: The first respondent answered correctly. What portion of my reply was wrong?