The human leg

[vinny11]

Main Question or Discussion Point

When kicking off the ground, what is the maximum amount of force that human's can exert?
Any references?

 

[meichenl]

rough estimate: 2000N

the world high jump record is 2.45m. A good high jumper can actually have his center of mass pass under the bar by arching around it, so say his center of mass rose to 2.40m. The dude who did it is 1.94m tall. The center of mass of a man is about .56 his height (hypertextbook.com/facts/2006/centerofmass.shtml), so that's 1.09m. So he jumped 1.31m. I don't know what he weighed, but 80kg is a reasonable guess. The impulse would have to have been 406 kg*m/s.

To figure out over how long a time that impulse was delivered, imagine he bent his knees to 90 degrees, then straightened them, lifting himself .5m before taking off. If his acceleration was constant in that time, it would have taken him .20 seconds, yielding a force of 2000N.

 

[meichenl]

on second thought, it should be more. people can deadlift 455kg, so that's 4500N right there.

 

[ddelaiarro]

What exactly do you mean by kicking?

meichenl gives two examples - a high jumper and a deadlifter. Personally, I'd classify both movements as pushing, not kicking...

 

[jbunten]

What exactly do you mean by kicking?

meichenl gives two examples - a high jumper and a deadlifter. Personally, I'd classify both movements as pushing, not kicking...

isn't a kick just a type of push?

 

[ddelaiarro]

well, I suppose it could be. But, when I 'hear' kick, I thinking of kicking a soccer ball or a football. I think we'd all agree that that movement is different than a pushing type movement...

 

[jbunten]

Hmm, In a way I see what you mean. When one kicks a ball properly (football=soccer ball to me I'm afraid) one stops applying force on contact with the ball and lets the transfer of momentum from the foot to the ball move the ball forward. However it really is a very related question.

vinny11 why do you assume he bent his knees to 90 degrees? High jumpers always start with a run so this assumption might be the problem with your calculation i.e I think the actual impulse lasts way less than 0.2 seconds.

check out this guy for instance:


even in slow mo his foot is in contact with the ground for far less than 0.2s.

 

[meichenl]

jbunten,

maybe it's less than .2 sec, although just by watching the video i can't tell. is there an easy way to count the number of frames it takes him to take off, and divide by the frame rate?

 

[DaveC426913]

Hmm, In a way I see what you mean. When one kicks a ball properly (football=soccer ball to me I'm afraid) one stops applying force on contact with the ball and lets the transfer of momentum from the foot to the ball move the ball forward. However it really is a very related question.

In fact, it's the same question. Over a duration approaching zero (i.e. before gravity is a significant factor), kicking a soccer ball is the same as kicking off a much much MUCH larger ball.