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kdog3683
United States916 Posts
As in me kicking a soccer ball, how do i calculate that force? I don't think i can with just the materials I have... Question: how do i devise a method so that I can control the amount of imput force? This is my idea. Take a baseball bat, weight it. poke the soccer ball with the tip as if you were playing pool. nvm... Just realized my weight would be added on to the baseball bat's. Any Ideas?   | ||
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fanatacist
10319 Posts
The instantaneous acceleration of the ball after you hit it, multiplied by the mass of the soccer ball, is equal to the force of the kick. Your baseball bat idea would work if you consider relative acceleration between the bat and the ball. | ||
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skyglow1
New Zealand3962 Posts
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datscilly
United States528 Posts
The time of contact in a soccer ball kick is ~11 milliseconds, found through google. Momentum can be calculated using the distance before it lands together with the initial angle. | ||
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Hypnosis
United States2061 Posts
On February 22 2008 06:44 fanatacist wrote: F = ma The instantaneous acceleration of the ball after you hit it, multiplied by the mass of the soccer ball, is equal to the force of the kick. Your baseball bat idea would work if you consider relative acceleration between the bat and the ball. To clear up what he is saying: The time of contact of your foot and the ball=instantaneous acceleration. Physics is sort of retarded because everything is based on things that are really hard or impossible to find (zero air resistance etc). you would have to round to find the time of contact then just multiply by the mass and air resistance and then you have to find out how far it went before it hit the ground and use that to calculate the horizontal acceleration and shit. | ||
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skyglow1
New Zealand3962 Posts
On February 22 2008 06:56 datscilly wrote: Another way to do it, if you cannot measure the acceleration of the ball right after it is kicked, is to use Energy = Force * Time. The time of contact in a soccer ball kick is ~11 milliseconds, found through google. Energy can be calculated either through the maximum height of the ball, or the distance before it lands together with the initial angle. You could also use something like force = (change in momentum) / time which might be easier cause you could measure the velocity as soon as the ball leaves the foot, and measure the time from when the foot first touches the ball then the ball leaves. | ||
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Luddite
United States2315 Posts
One way I can think of doing this would be to record yourself kicking the ball on a video camera. By watching the video, you'll be able to see how long you were making contact with the ball, and how fast it was going after you kicked it. weigh the ball, calculate how much energy it had after you kicked it (1/2 * M * V^2), and then divide the energy by the distance over which you kicked it (work = force * distance). That's sort of a quick and dirty method for finding the AVERAGE amount of force you put on the ball. If you want more detailed information, you'll need fancier equipment. For example, you could put some little springs inside the ball, and have a computer record how far the springs compress as you kick it. That could tell you how much force you're applying at any given time. Hope this helps. | ||
Chill
Calgary25977 Posts
Assume no losses and solve for kinetic energy: iPE - fPE = m1g(h1-h2) = 0.5m2v^2 v = SQRT(2g(h2-h2)(m1/m2)) Get the masses (measure) and now you have velocity (solved). I'm sure you could translate into force in a varierty of ways, from assuming friction and using distance to stop, or using a camera and seeing the time of contact. Someone probably has a better idea. You could also order a $5 load cell...  | ||
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datscilly
United States528 Posts
On February 22 2008 08:05 skyglow1 wrote: You could also use something like force = (change in momentum) / time which might be easier cause you could measure the velocity as soon as the ball leaves the foot, and measure the time from when the foot first touches the ball then the ball leaves. this is wrong | ||
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Plutonium
United States2217 Posts
Kick the ball and measure the angle the rope makes with the vertical. Easiest way to do this would to just have another person on a stepladder on the side with a protractor. The force of your kick will translate into the potential energy of the height, so use trigonometry to calculate how high the ball rose. The Equation is: KE = MGH aka Kinetic Energy (The force of your kick in Joules) = Mass of ball (kg) x 9.8 meters/second x height ball rose off of ground(meters) | ||
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Luddite
United States2315 Posts
On February 22 2008 08:52 datscilly wrote: Force = (change in Momentum) / Distance is the correct equation. Distance would be the distance over which the force acts on the ball, and force would be the average force over that distance. No he was right. Force = (change in momentum)/time, or (change in energy)/distance. Doesn't really matter which you use, because either way you just end up measuring the velocity of the ball. | ||
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Plutonium
United States2217 Posts
Because some of your suggestions pretty much require him to have slow-motion cameras. Also, my way's the easiest. | ||
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Luddite
United States2315 Posts
On February 22 2008 09:04 Plutonium wrote: Get a tetherball or any sort of soccer-sized ball on a string, weigh it, and tie it something like the crossbar of a soccer goal, and then measure how far off the ground it is, or to make your life easy, just lengthen the string so it's touching the ground. Kick it and measure the angle the rope makes with the vertical. Easist way to do this would to just have another person on a stepladder on the side with a protractor. The force of your kick will translate into the potential energy of the height, so use trigonometry to calculate how high the ball rose. Kinetic Energy (The force of your kick in Joules) = Mass of ball (kg) x 9.8 meters/second x Height (meters) This is a good idea, except I'm pretty sure he could kick the ball high enough to get it all the way up (so that it runs out of rope.). You'd have to either tie to by a really long string to something really tall like a building (hard to set up), or else use a really heavy ball... and kicking a really heavy ball is painful. | ||
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Plutonium
United States2217 Posts
Also, why do I keep telling this guy how to do awesome physics experiments with homemade materials? This is the same guy who thought it would be fine to heat oil over an open flame. /Isn't Bill Nye. | ||
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BluzMan
Russian Federation4235 Posts
Your problem, however, seems quite strange. Unless you want to do a crash test, there's no other need for the force (or acceleration, they're the same thing). You usually measure acceleration in pulse-like processes when you want to test if something breaks. Otherwise, it means close to nothing. It's much like with pulse lasers - at the first glance, a terawatt sounds like a lot, but the duration of the pulse is a femtosecond, so the actual energy is puny. | ||
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BluzMan
Russian Federation4235 Posts
On February 22 2008 07:37 Hypnosis wrote: To clear up what he is saying: The time of contact of your foot and the ball=instantaneous acceleration. Physics is sort of retarded because everything is based on things that are really hard or impossible to find (zero air resistance etc). you would have to round to find the time of contact then just multiply by the mass and air resistance and then you have to find out how far it went before it hit the ground and use that to calculate the horizontal acceleration and shit. Retarded physics gave your sorry ass a computer, so shut the fuck up please. | ||
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Plutonium
United States2217 Posts
I think we're just doing his homework for him. | ||
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Luddite
United States2315 Posts
The really hard question of course, is how much error is involved in measuring the force? | ||
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SpiritoftheTunA
United States20903 Posts
the person saying energy = force * time is just plain wrong all the people mentioning time are thinking of impulse, not force OR energy the time of contact between your foot and the ball is NOT instantaneous acceleration you guys are fucked up edit: oh, and the person mentioning elasticity (probably something to do with coefficient of restitution) is severely overestimating your physics class the person saying force = change in momentum / distance is a fucking moron the person who said force = change in momentum (impulse) / time is right though (assuming they meant duration of impact) | ||
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Chill
Calgary25977 Posts
On February 22 2008 09:44 SpiritoftheTuna wrote: most of the people saying use kinetic energy = potential energy are forgetting the horizontal element of the velocity that contributes to the energy EDIT: and aren't relating it back to the force anyway the person saying energy = force * time is just plain wrong all the people mentioning time are thinking of impulse, not force OR energy the time of contact between your foot and the ball is NOT instantaneous acceleration you guys are fucked up edit: oh, and the person mentioning elasticity (probably something to do with coefficient of restitution) is severely overestimating your physics class the person saying force = change in momentum / distance is a fucking moron the person who said force = change in momentum (impulse) / time is right though (assuming they meant duration of impact) Thanks for your help and suggestions to help the OP! | ||
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SpiritoftheTunA
United States20903 Posts
On February 22 2008 12:30 Chill wrote: Thanks for your help and suggestions to help the OP! yeah no problem, same to you by the way well i mean, OP didn't mention what he's able to measure. time of impact, instant accel (easily), get a graph of position vs time up, or what. it's pretty impossible to make a suggestion from what he gave me. so hey, kdog... whatcha got? edit: to improve on chill's pendulum idea though, ok... (just to make everything easier to measure) tie a ball to a string, hang it vertically, make sure it's stationary kick it lightly measure the angle it deviates from the vertical (with a protractor facing down, oriented around the pivot point) also measure the time it took to get to that angle 1/2mvsquared = mgh where h = L (length of pendulum) - Lcostheta where theta is angle from vertical find out v (which will be initial velocity) find out time of impact divide for accel multiply by mass for force or something | ||
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skyglow1
New Zealand3962 Posts
The idea of using a video cam would work really well with this I think if you could have a high enough frame rate. You could put some sort of a scale behind the ball which has really clear divisions at every 1 cm or somethinng to measure the velocity of the ball just after it leaves the foot, and you could measure how long in contact the foot is with the ball, adn measure the mass of the ball. | ||
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