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Does human weight equal strength

Postby wildcat » Sun Dec 02, 2007 9:02 am

I having problems researching this topic on the internet? Do you have any suggested web sites? would this topic fall under kinetics? :x

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Re: Does human weight equal strength

Postby Louise » Sun Dec 02, 2007 9:49 am

wildcat wrote:I having problems researching this topic on the internet? Do you have any suggested web sites? would this topic fall under kinetics? :x

I'm not exactly sure what your project is. Is this a sciencebuddies project or is it from somewhere else? Could you provide a link?

The relationship between strength and weight is not straight forward. Much of this depends on the specific task. Generally, it is the amount of muscle not the total weight that is important, but there are certain cases where total weight may help. Think of a game of tug-of-war for example. Just being 'heavy' and standing still means that you can resist the other teams pulling. In this case, the muscle strength plus the total weight would make a person appear to be very strong.

I think this topic will be difficult to do a science fair project on. I cannot see what the variables would be in this project.

If you can write back with more detail we can help more.

There are also some suggested sports related topics here, which might be interesting to you:

Good luck!

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Postby Craig_Bridge » Sun Dec 02, 2007 10:14 am

Many human strength tests involve lifting a known weight either directly or by pulling or pushing on something through some mechanism to lift the weight. These measurements tend to fall into the catagory of "static" forces.

Kinetics is usually the study of things in motion.

While the weight is lifted in the strength tests and that takes energy, the measurement is involved is the "static" force that must be overcome in order for the weight to be lifted.

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Postby vishwa » Sun Dec 02, 2007 11:51 am

"Weight" of humans is a static variable as it is more of a force exerted by your body mass (not a continuously variable parameter) on the ground reference.
But when you exert strength to do something/anything, a component of "force" acts on the object in the direction of applied force, and in this case, depends on the force applied by your extremities on the same.
Let's consider a test case - that of pulling a mass "m" with a velocity "v" horizontally at the ground level. Then the force that you have to overcome is the frictional force b/w the object and the ground apart from the inertia. But when you do the same on an incline (inclined at an angle "theta", say), you also have to overcome "m times g times sin(theta)" the component of the weight of the object that is acting against you, making your job harder :). This is where you have to apply more "strength" or force. Keep in mind though, that there indeed needs to be a "minimum" force applied to move the object, e.g. a toddler couldn't move a suitcase whereas an adult could.
So, for your research, you could consider test cases where you exclusively vary weights (i.e. masses) of objects and then find out how they relate to the strength (force) needed to overcome those. You could also use different control variables like smoother surfaces, inclines etc.

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Postby wildcat » Sun Dec 02, 2007 8:55 pm

ok, thanks for the inputs. Specifically, I am doing a project to determine if a persons actual weight equals his or her strength, i.e., the amount of weight they can lift. For instance, a person weighs 280lbs then does his muscle strength that is can he at least lift 280lbs which is equal to his body weight.

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Postby bradleyshanrock-solberg » Mon Dec 03, 2007 7:56 pm

Strength is usually expressed in the ability to perform a certain task.

Olympic weightlifters, for example, distnguish between the ability to get an object off the ground while standing erect (dead lift) vs the ability to "press" the object over their head while standing or lying down.

A martial artist or boxer will define "strength" as "how hard can I hit that bag" (or another person). Muscles and mass help, but your technique also matters a lot (how you use the leverage of your body, whether you can push off the ground and translate that force into your punch or kick, whether you instead get some extra force by movement - a lunge or "flying kick", and also the state of the opponent - whether he can deflect the attack, "roll with it", is off balance etc)

A sumo wrestler defines "strength" as "can I push the other guy, or can he push me". This is a mix of muscles, how much you weigh, how low your center of gravity is, and technique (your body is a series of levers (bones) and you can lock them in a way to cause force sideways to go down into the ground...football players do this too when linemen go up against each other)

You need to define strength. You need to also limit what the human can do in terms of technique. (martial arts are too variable....something like olympic weightlifting is better, it's designed to minimize this variable).

You really also need to measure muscle mass as a percentage of body weight. Someone who weighs 200lb because he eats potato chips and watches TV all day is not going to have the same strength as the guy who is 200lb because he works out in the gym every day....the first guy is mostly fat, the second is mostly muscle. There's also the matter of what kind of strength...men and women both have good leg strength, but men have better upper body strength pound for pound than women, even with similar muscle mass indexes. Men also have an easier time having very high muscle mass compared to women.

My instinct is that your question isn't well defined. Both Strength and Weight are vague terms.

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