Slightly Pointless Math Question

[tkioz]

So it's been a -long- time since I was in high school but I doing a bit of day dreaming today about space based weapons (long story) and I was wondering something; I know mass * velocity = force but for the life of me I can't remember where area comes into it, if it does at all, or is that covered by penetration?

 

[JenSeven]

You mean Area of Impact?
In that case, better grab yourself a science book.

First you need to work out what you're shooting (projectiles, lasers, whatever) and the diameter of that (this is very important to some later calculations).
Then the speed at which your projectile is traveling.
Then if there is any resistance to your traveling projectile (like a gravitational pull from a nearby stellar object and if you want to penetrate several atmospheric layers).
After that, what is it that you are hitting (metal, dirt, water, flesh) and the density of that abject.
And if you want to know the area affected by your shot, you'll need to know how big the projectile is, the substance from which it's made and if it's explosive or not.

I probably missed a few things too, since I'm not a true scientist, but this should get you pretty far.

 

[tkioz]

You mean Area of Impact?
In that case, better grab yourself a science book.

First you need to work out what you're shooting (projectiles, lasers, whatever) and the diameter of that (this is very important to some later calculations).
Then the speed at which your projectile is traveling.
Then if there is any resistance to your traveling projectile (like a gravitational pull from a nearby stellar object and if you want to penetrate several atmospheric layers).
After that, what is it that you are hitting (metal, dirt, water, flesh) and the density of that abject.
And if you want to know the area affected by your shot, you'll need to know how big the projectile is, the substance from which it's made and if it's explosive or not.

I probably missed a few things too, since I'm not a true scientist, but this should get you pretty far.

Cool thanks, that's pretty much what I want (I think).

I know for example a 100 kilogram object moving at 1000 meters per second hits with the force of 100,000 newtons, and an object of 10 kilograms moving at 10,000 meters per second hits with the same force, but if I have two objects, both weighing 10 kilograms moving at 10,000 meters per second but one is the size of a 10 cent piece and one is the size of a dinner plate which hits harder.

 

[JenSeven]

The 10 cent piece hits harder, due to a smaller surface are that it s hitting, so it's exerting the same amount of force as the dinner plate but over a smaller surface area.
This being Newtons per square inch (or centimeter).

 

[tkioz]

The 10 cent piece hits harder, due to a smaller surface are that it s hitting, so it's exerting the same amount of force as the dinner plate but over a smaller surface area.
This being Newtons per square inch (or centimeter).

Ahh cool thanks, I knew I should have paid more attention in high school.

 

[MrDumpkins]

It's actually this equation:

Mass*Acceleration=Force

Acceleration is just the derivative of velocity.

 

[WopWopWop]

What JenSeven is talking about is Pressure.
Force=Pressure*Area
Also, I'm probably just going to be the first of few but it is in fact:
Force=Mass*Acceleration

 

[JenSeven]

What JenSeven is talking about is Pressure.
Force=Pressure*Area
Also, I'm probably just going to be the first of few but it is in fact:
Force=Mass*Acceleration

Well, he wanted to know what would hit harder, a large object or smaller object that has the same weight and speed as each other. That would lead me to using this. It would seem much more logical than any other, atleast to me, but I don't really know all that much about science.

 

[Fire Daemon]

One thing I want to point out is that the formula you're thinking of (Newton's Second Law) is actually Force = Mass x acceleration, not velocity. Acceleration is the rate of change in velocity over time, so there will be a difference if you get the two wrong. Just thought I should mention that in case someone who should be studying for a Physics exam come in here and makes that mistake later on.

EDIT: As I was typing this someone beat me to it. Curses.

 

[Redingold]

Mass times velocity is momentum, not force. Momentum over time is force, and force over area is pressure.

 

[WopWopWop]

What JenSeven is talking about is Pressure.
Force=Pressure*Area
Also, I'm probably just going to be the first of few but it is in fact:
Force=Mass*Acceleration

Well, he wanted to know what would hit harder, a large object or smaller object that has the same weight and speed as each other. That would lead me to using this. It would seem much more logical than any other, atleast to me, but I don't really know all that much about science.

I wasn't correcting you, my friend, but simply terming the measurement for which you provided the units

Also, to tkioz, the formula you are probably thinking of/looking for is:
Kinetic Energy=0.5*mass*velocity^2
This is the layman's formula for any given scenario.

 

[WopWopWop]

You mean Area of Impact?
In that case, better grab yourself a science book.

First you need to work out what you're shooting (projectiles, lasers, whatever) and the diameter of that (this is very important to some later calculations).
Then the speed at which your projectile is traveling.
Then if there is any resistance to your traveling projectile (like a gravitational pull from a nearby stellar object and if you want to penetrate several atmospheric layers).
After that, what is it that you are hitting (metal, dirt, water, flesh) and the density of that abject.
And if you want to know the area affected by your shot, you'll need to know how big the projectile is, the substance from which it's made and if it's explosive or not.

I probably missed a few things too, since I'm not a true scientist, but this should get you pretty far.

Cool thanks, that's pretty much what I want (I think).

I know for example a 100 kilogram object moving at 1000 meters per second hits with the force of 100,000 newtons, and an object of 10 kilograms moving at 10,000 meters per second hits with the same force, but if I have two objects, both weighing 10 kilograms moving at 10,000 meters per second but one is the size of a 10 cent piece and one is the size of a dinner plate which hits harder.

That's force over the surface area, which is easy to explain with the bed of nails analogy.

A man steps on a nail, it goes through his foot, the same man steps on a whole shoe (or wooden plank or something) made of nails, the man's foot does not go through. His force (this one caused by weight and gravity) is the same, but the area over which he spreads it is different and therefore penetration of his foot is different.

Genau.

So, to clarify the matter, both objects will hit just as hard as each other but the smaller object will have greater penetrating strength.

 

[Cazza]

wolframalpha is a great site for research when you can't remeber yr 11 maths. Helps me lots.
http://www.wolframalpha.com/

 

[Aerodyamic]

Can we just make a youtube video showing some hitting a melon with a small hammer and a big hammer? That seems like way more fun that mathing up a answer.

*RAWWWWR SMASHIE SMASHIE SPLAT*

Myth bu.... smooshed?