joule calculation

Sam Salvati

Sam Salvati

Joined
Aug 6, 2007
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I was wondering if anyone better at math than I am could help me figure out how many joules of force a 150 pound eight falling 5,10, and 15 feet would generate? a 20 pound weight falling the same distances?
 
150 lbs falling 5 feet = 999.6J
10ft = 2032.52J
15ft = 3065.44J

20lb weight
5ft= 135.46J
10ft= 270.925J
15ft= 408.876J
 
Sam, you don't have all the numbers there. For joules you will need weight, distance, and time. If the weight is just dropped at sea level what you are calculation is the potential energy released. You can use the gravitational acceleration as the time factor, 9.8 , thus the formula is PE=mgh.
A calculator is found here:
http://hyperphysics.phy-astr.gsu.edu/hbase/flobi.html

The answers given by Craig are correct.

One of your problems might be a language barrier.To do work problems in joules newtons and ergs, talk in metric measurements. To work in foot pounds and horsepower, use English units. It is far easier to use the metric calculations.

When doing quick and approximate calculations, use 10 as the gravitational factor, .3 as the factor to convert a feet to meters, and .5 as the factor to convert pounds into Kilograms . Take 10% off the result and you will be close enough.( using these numbers, you can do the math in your head. Or in Sam's case, with a piece of charcoal on the back of a shovel)
So, with your numbers a quick and dirty calculation would be :
20 lbs X .5 = 10kg
5ft X .3 = 1.5 meters

PE= 10X10X1.5= 150 -10% = about 135joules
 
Not to kick a dead horse, but units matter here. Based on the question of how much FORCE a falling weight will generate, it's more of a question of change in momentum than simple potential energy calculations. Then you have to get into what type of collision it is (elastic, inelastic, or somewhere in between), as well as how much deformation occurs in the colliding materials. This will affect the time it takes the falling weight to slow down to a stop. The shorter the time to stop, the higher the force. Likewise if you take longer to slow down the resulting force is lower. Think car crashes and airbags here. . .

At any rate, Joules are units of energy. Force, however, is measured in Newtons (or Pounds-Force for you English units types), not Joules. Completely different concept here between the two units. Force is the by-product of expending energy (i.e. doing work) on an object.

Sorry to be such a nitpicker, but this stuff is near and dear to my heart.
 
Thanks guys!!!! wish I paid more attention to Math itself than the math teacherwas.

How would I calculate foot pounds and/or psi of force for the same 5, 10, 15 foot drops of the 150 pound weight?

Can you tell drop hammers are on my mind?
 
My personal advice you can crunch numbers and that's good and all, but at some point you just gotta go with your gut and try something. You'll know it's where you want it when you see it in action.

I would have a hard time believing you could crunch the numbers to find an mount of force you wanted.

Pressure is force per unit area. You'll need to calculate the amount of force the weight inflicts upon the designate victim. Which will require you to know the impulse of the impact as well as the area that the impact occurs over. It requires a bit more information that we have. It also isn't a fixed number, depending on the hardness of the material it will be more or less.
 
I'm just thinking about things and trying to get more info is all. I am out of curiosity trying to figure out how much force is applied when a 150 pound weight with a 3" by 4" contact die is dropped and contacts another 3" by 4" bottom die. I'm gonna build it either way hehe.
 
Like 65535 already said... at the end of the day you will just have a bunch of numbers that you wont be able to relate to anything other than the numbers are bigger as the mass gets bigger.

Look around on the net and see what size head others are using on their hammers to do similar work and you will find your answer. Bigger is better if you are building a drop hammer, so make it as big as you can afford to go. You know as well as I do, as soon as you build it, a bigger project will come thru the door and youll be wishing you went bigger in the first place.

Brad
 
Foot pounds is exactly that. If a 150 pound weight drops 4 feet, it develops 600 foot pounds ( 150 pounds moving through 4 feet). One thing to remember is that it takes the same amount of effort to lift the weight back up for the next drop.

As have been said, there are infinite scientific and physics variables that will affect the actual amount of energy transferred, but for a drop hammer, just figure the simple math.

The real place that there is some math involved is the anvil/ram surface.
The smaller the striking spot, the higher the impact in PSI. a 4X4" anvil/ram covers 16 sq.in., so the above setup will deliver almost 40 PSI. The same setup with a 3X3 anvil will deliver over 60 PSI . Take that down to a 1X1" contact and it jumps to 600PSI.

I agree with "old U238" (DU), The basic design is simple. Build it and fine tune the things that make it complex ( like harmonics).

On the subject, if you could get your hands on a hundred kilos of depleted uranium, you could build a killer ( bad pun) drop forge.
 
Brad, yeah bigger is always better, but free steel is free steel hehe.

Stacy, the head would be very small :D
 
Not as small as you would think. Depleted uranium is only 2.5 times as dense as iron. Gold is denser than uranium. Now, platinum would be cool.
 
Is platinum heavy like gold or heavier?

I think it's funny that a metal like gold is so prized, it really is fairly weak and useless for utilitarian things hehe

Gold is for the mistress -- silver for the maid --
Copper for the craftsman cunning at his trade."
"Good!" said the Baron, sitting in his hall,
"But Iron -- Cold Iron -- is master of them all."
 
Sam, Pure gold has a density of 19.3 grams / cubic centimeter. Platinum is 21.4. Osmium is 22.6 if you want to max it out. Just for comparison, Iron is about 7.8.

And BTW, there are metal properties that are useful besides hardness. Ductility, thermal conductivity, electrical conductivity, resistance to corrosion. Gold is at or near the top for all of these.

You can hammer gold thin enough to see through it. Concentrated nitric acid won't touch it. Just try that with steel... -Doug (former chemist)
 
Doug beat me to it.

You can do things with gold and platinum that can't be done with iron. A wedding band can be drawn into miles of wire, thinner than a hair. A pound of gold can be drawn into a wire that will circle the earth. Entire mosque/church roofs have been gilded in thin sheets of gold.
Platinum's high melting point makes it superb for many tasks.

Stacy ( former chemist)
 
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