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Active: 18636 users

help physics question

Blogs > kdog3683
Post a Reply
1 2 Next All
kdog3683
Profile Blog Joined January 2007
United States916 Posts
February 21 2008 21:40 GMT
#1
How do i calculate the force of a kick?

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?

*
Multiply your efforts.
fanatacist
Profile Blog Joined August 2007
10319 Posts
February 21 2008 21:44 GMT
#2
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.
Peace~
skyglow1
Profile Blog Joined April 2005
New Zealand3962 Posts
February 21 2008 21:45 GMT
#3
What materials do you have? If you wanna measure the force of a kick, just use F=ma and measure the acceleration of the ball and its mass and multiply them together.
datscilly
Profile Blog Joined November 2007
United States528 Posts
Last Edited: 2008-02-22 03:24:55
February 21 2008 21:56 GMT
#4
Another way to do it, if you cannot measure the acceleration of the ball right after it is kicked, is to use Momentum = Force * Time.

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.
Hypnosis
Profile Blog Joined October 2007
United States2061 Posts
February 21 2008 22:37 GMT
#5
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.
Science without religion is lame, Religion without science is blind
skyglow1
Profile Blog Joined April 2005
New Zealand3962 Posts
February 21 2008 23:05 GMT
#6
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.
Luddite
Profile Blog Joined April 2007
United States2315 Posts
February 21 2008 23:09 GMT
#7
This is an interesting question. The problem is that the soccer ball isn't at (all the sort of ideal object that you'd like it to be. It compresses a lot. You'll make contact for a long time, putting force on the ball the whole time, and the force will be constantly changing as the ball compresses.

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.
Can't believe I'm still here playing this same game
Chill
Profile Blog Joined January 2005
Calgary25977 Posts
Last Edited: 2008-02-21 23:34:14
February 21 2008 23:32 GMT
#8
Use a pendulum. Start it at a known mass and height. That = initial potential energy. Let it freefall and smack the ball and then see how high the pendulum ends on the other side. That = final potential energy.

Assume no losses and solve for kinetic energy:
iPE - fPE = iKE - fKE
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...
Moderator
datscilly
Profile Blog Joined November 2007
United States528 Posts
Last Edited: 2008-02-22 03:23:15
February 21 2008 23:52 GMT
#9
On February 22 2008 08:05 skyglow1 wrote:
Show nested quote +
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.


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.

this is wrong
Plutonium
Profile Joined November 2007
United States2217 Posts
Last Edited: 2008-02-22 00:18:15
February 22 2008 00:04 GMT
#10
Get a tetherball or a soccer ball tied to a string or rope, weigh it, tie the other end off to something like the crossbar of a soccer goal or an overhead beam, and lengthen the string so that the ball's just touching the ground.

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)




Luddite
Profile Blog Joined April 2007
United States2315 Posts
February 22 2008 00:04 GMT
#11
On February 22 2008 08:52 datscilly wrote:
Show nested quote +
On February 22 2008 08:05 skyglow1 wrote:
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.


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.
Can't believe I'm still here playing this same game
Plutonium
Profile Joined November 2007
United States2217 Posts
Last Edited: 2008-02-22 00:12:04
February 22 2008 00:09 GMT
#12
Is he looking for a theoretical way, or a practical way, like if he has to do it with home-made materials?

Because some of your suggestions pretty much require him to have slow-motion cameras.

Also, my way's the easiest.
Luddite
Profile Blog Joined April 2007
United States2315 Posts
February 22 2008 00:19 GMT
#13
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.
Can't believe I'm still here playing this same game
Plutonium
Profile Joined November 2007
United States2217 Posts
Last Edited: 2008-02-22 00:23:36
February 22 2008 00:20 GMT
#14
He never said anything about measuring his hardest kick, just any kick.

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.
BluzMan
Profile Blog Joined April 2006
Russian Federation4235 Posts
February 22 2008 00:24 GMT
#15
You need to know the elastic properties of the ball (or, to be more precise, the elastical properties of the process), otherwise, it's unsoluble. "Imperfect" hit means it has a duration, if you assume the hit is perfect, it's duration is zero, force is infinity.

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.
You want 20 good men, but you need a bad pussy.
BluzMan
Profile Blog Joined April 2006
Russian Federation4235 Posts
February 22 2008 00:25 GMT
#16
On February 22 2008 07:37 Hypnosis wrote:
Show nested quote +
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.


Retarded physics gave your sorry ass a computer, so shut the fuck up please.
You want 20 good men, but you need a bad pussy.
Plutonium
Profile Joined November 2007
United States2217 Posts
February 22 2008 00:26 GMT
#17
True, the ballistic pendulum approach would only work in the situation of a pure inelastic collision, though he could just do the same thing by pushing a bowling ball, which wouldn't lose energy through deformation.

I think we're just doing his homework for him.
Luddite
Profile Blog Joined April 2007
United States2315 Posts
February 22 2008 00:37 GMT
#18
haha yeah, he should be doing it, not us. Still, I think it's fun to think about these sorts of problems.

The really hard question of course, is how much error is involved in measuring the force?
Can't believe I'm still here playing this same game
SpiritoftheTunA
Profile Blog Joined August 2006
United States20903 Posts
Last Edited: 2008-02-22 00:48:26
February 22 2008 00:44 GMT
#19
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)
posting on liquid sites in current year
Chill
Profile Blog Joined January 2005
Calgary25977 Posts
Last Edited: 2008-02-22 03:31:07
February 22 2008 03:30 GMT
#20
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!
Moderator
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