# Impact

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I tried looking at the formulas at a site, and I had no real idea of what I was looking at. All I'm really looking for are some generalities anyway. (Although if someone wants to take a swing at even pointing me in the right direction of the right formulas that would be a start.)

Basically, a 0.4 pound object traveling at 73.3 feet per second would impact on a target with what kind of force?

The other item I'm trying to get a grasp on, is a 80 pound object that is thrown (so I really don't know how fast it would be going) would impact on a target with what kind of force?

Any help would be appreciated.

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What do you mean "what type of force"?

Are you looking for the answer: a contact force?

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No, I mean 'what kind of force' as in a measurement of impact (?); a measurement of damage; a measurement of force.

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Well force is equal to change in momentum divide by change in time or

F = d(mv) / dt

Where mv is mass x velocity (which equals momentum) and t is time.

And remember that momentum is conserved, ie. total momentum at the end of collision is equal to the total momentum from before they collided.

That's enough to answer the question, however you have a lot of non-SI units and so I don't know if you just stick those numbers into the equations and even if you did you'd get a weird unit as your end answer anyway.

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As 5614 implied, the force felt depends on the impact time. Without that information the question of impact force is meaningless. Momentum and energy are the relevant parameters, and the efficiency with which you transfer the energy.

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I doubt you're actually looking for a force.

I was in what might be the same position as you a while ago. Looking stuff up in forces I just got confused. Instead look at kinetic energy. The equation for kinetic energy is energy equals one half mass times velocity squared:

E=0.5mv^2

E is energy in Joules. m is mass in kilograms. v is velocity in meters per second (so you'll have to convert your units). If you are looking for a force, you need extra information. But with this formula you can find how much energy a moving body has, and that amount of energy is released when it is stopped.

A good example is a meteor impact. You have an asteriod that wieghs 40000kg. Its moving at 15000m/s. How much energy does it release when it hits the earth? Well its .05 x 20000 x 15000 x 15000 = 4.5*10^12 J. Which is a lot. If we want to make that number mean something, lets compare it to a nuclear bomb. The bomb that took our Hiroshima was around 13 kilotons. Meaning it released energy of 13 thousand tons of TNT. Well it turns out that 1 kiloton of TNT is equal to 4.2*10^12J. Do the division, and it turns out that meteor hit the ground with the energy of 1.07 thousand tons of TNT. With that formula you can find the energy of a moving body, and compare it to some unit that you already know, for scale (which you can look up).

Of course this may be of no use to you at all. Its just how I learned this sort of thing when I was in a similar situation.

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Small correction to the above post

E=0.5*mv2

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Small correction to the above post

E=0.5*mv2

Hahahaha, oh man I can't believe I made that mistake, I've had that formula memorized for like 4 years now. Thanks for seeing that.

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