Author Topic: Drop question  (Read 2882 times)

Offline Shane Warren

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Drop question
« on: February 05, 2009, 06:45:22 PM »
I'm pretty sure I'm right but i want a second opinion
when doing a drop the more forward momentum you have the shallower the angle of your landing.
if you maximize your forward momentum wouldn't you also minimize the stress on your body when you land?
assuming you roll of course.
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Offline Mathew C

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Re: Drop question
« Reply #1 on: February 05, 2009, 07:42:46 PM »
No

Vertical and lateral momentum and two independent vectors. Your forward momentum has no affect on how quickly you move downwards, aside from the fact that rolling safely requires a moderate amount of forward momentum. Furthermore, if you assume that you are always rolling, any increase in forward momentum will increase the stress, because it increases the force that your have to absorb.

Offline Dan Elric

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Re: Drop question
« Reply #2 on: February 05, 2009, 08:14:45 PM »
The physics of what you're asking become rather difficult.  It really depends on how good your form is.  By using muscles to absorb the impact you experience a positive acceleration to counteract the negative acceleration of gravity.  Nonetheless the force of gravity will always be constant regardless.  You will hit the ground at the same time whether you just dropped off of a ledge or jumped off of one.  One of these days I'll come up with a basic physics example to prove the difference.  In a proper roll you don't actually absorb much impact at all, rather your feet should act as a pivot and you should fall forward, and then you use the roll to turn the downward momentum into forward momentum.  This is only with proper form.  Which after a year of training I have still not attained.
The reason a jump with forward momentum is easier than a straight drop is because the roll will be easier to fall into, because while your feet will have stopped moving forward, the rest of your body will still have a horizontal velocity and inertia will literally push you forward and allow you to pivot easier.  Ultimately it depends on how good your form is.

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Re: Drop question
« Reply #3 on: February 05, 2009, 08:24:26 PM »
actually horizontal momentum can sometimes make it worse on your body, because doing a proper landing or a roll can be harder if you are moving forward with enough momentum, at least in my experience its easier to do those things with little forward momentum

Offline Dan Frank

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Re: Drop question
« Reply #4 on: February 07, 2009, 08:42:28 PM »
Forward momentum doesn't make a difference because of the angle. The function of the roll is to a)absorb impact all over your body rather than just on your legs, and b) to increase the time it takes to absorb the impact (I think.)
In a proper roll you don't actually absorb much impact at all, rather your feet should act as a pivot and you should fall forward, and then you use the roll to turn the downward momentum into forward momentum.  This is only with proper form.

I haven't heard this before... do you have actual physics behind this, or did you think of it yourself? It seems to make sense at first, but then I don't think there is a way to change the direction of momentum. I'd be very interested to know what's going on if that's how it works.
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Offline Mathew C

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Re: Drop question
« Reply #5 on: February 07, 2009, 09:15:19 PM »
No matter what, your body takes the same amount of force. It's just a matter of what parts of your body take the blow. Ideally, every muscle in your body would exert a proportionate amount of force, and as much force as safely possible would be absorbed by other parts (i.e. taking a ht with your shoulder). Unfortunately, this ideal situation is impossible due to physics and the mechanics of our bodies.

As for rolls, your posterior chain still absorbs 90% of the force along the y axis. The only difference is that force along the X axis is preserved, instead of being absorbed by your legs, so you never stop moving forward. Unless you have forward momentum, roll vs. no roll makes no difference in the force you exert upon landing.

Offline Dan Frank

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Re: Drop question
« Reply #6 on: February 07, 2009, 10:40:04 PM »
Unless you have forward momentum, roll vs. no roll makes no difference in the force you exert upon landing.

But am I right in saying that it has everything to with the power? With a bigger time frame, the power decreases, no?
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Offline Mathew C

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Re: Drop question
« Reply #7 on: February 08, 2009, 07:05:25 AM »
Unless you have forward momentum, roll vs. no roll makes no difference in the force you exert upon landing.

But am I right in saying that it has everything to with the power? With a bigger time frame, the power decreases, no?

whaaa? Time frame for what? I'm lost. What are you talking about?

Offline Dan Frank

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Re: Drop question
« Reply #8 on: February 08, 2009, 11:08:31 AM »
Power equals work over time. (P=W/t) Therefore an increase in time equals a decrease in power.


Or you could say force equals acceleration over time. (F=a/t) Therefore an increase in time equals a decrease in power.
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Offline Matthew Wang

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Re: Drop question
« Reply #9 on: February 08, 2009, 11:13:03 AM »
Rolling DOES shift your downward momentum (If you do the advanced roll that is) into forward momentum. It also spreads the shock you would receive from the downward momentum along the ground by spreading it out. The more you spread out the shock on the ground, the less impact your body takes. That's why in the advanced roll you see people pushing off the ground and sort of diving into the roll.
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Offline Dan Frank

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Re: Drop question
« Reply #10 on: February 08, 2009, 11:27:49 AM »
Rolling DOES shift your downward momentum (If you do the advanced roll that is) into forward momentum.

Can you explain this? Obviously you start moving in a different direction, but in what way does an increase in momentum on the x-axis affect the momentum on the y-axis? I don't see it making a difference, but I'm up for an explanation.
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Offline Sam Slater

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Re: Drop question
« Reply #11 on: February 09, 2009, 08:28:35 AM »
The force or power that the body incurs is not changed, it is simply spread out across the body during the roll.

In a straight drop, the force must be absorbed vertically.  Thus the force must be absorbed by the muscles in order to prevent the body from being damaged.  Because the body is also essentially vertical, the mass in the equation posted above is the full mass of the person dropping.

When forward momentum is added, it allows for the proper execution of the roll.  What the roll does is spread out both the area of impact and by extension the time of the impact.

As you land with the forward momentum, you legs absorb some of the downward momentum, but because you (should) be leaning forward, the amount of mass that is above them is less, so they take less impact.  Your legs use the energy loaded in them as they absorb this impact, and explode forward and slightly upward to assist in positioning the body for the next step.  The mass that is still falling (your upper body) now starts to prepare for the roll.

When you roll, you are constantly absorbing the downward momentum.  If done correctly, different parts or points on the body are each gradually receiving and absorbing the impact of the fall as they roll forward.  This spreads out the impact across these points all because you rounded your body.  This is assuming you did the roll correctly and didn't absorb all the impact with your shoulder or back first and then finish the roll.

Hopefully that explains the physics behind it.  I have never tested this in a lab with force reading and what not, however this is the explanation that i have been able to extrapolate based upon my admittedly limited knowledge of physics, my understanding of the roll, and my ability to apply logic to connect the two.

Offline Dan Frank

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Re: Drop question
« Reply #12 on: February 09, 2009, 12:05:08 PM »
@Sam, that's exactly what I thought. We need to get something like this stickied.
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Offline Dan Elric

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Re: Drop question
« Reply #13 on: February 09, 2009, 02:18:12 PM »
Quote
Or you could say force equals acceleration over time. (F=a/t) Therefore an increase in time equals a decrease in power.
F = ma, not a/t.

Quote
I haven't heard this before... do you have actual physics behind this, or did you think of it yourself? It seems to make sense at first, but then I don't think there is a way to change the direction of momentum. I'd be very interested to know what's going on if that's how it works.
I theorized it myself, but it is based off what Dan Edwards said about a proper roll.  He said your body should automatically fall over when you roll, or something along those lines.  And you can redirect forces using angles.  Also, when you push down on one side of a wheel what happens?  It spins.

Offline Dan Frank

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Re: Drop question
« Reply #14 on: February 09, 2009, 02:53:32 PM »
Quote
Or you could say force equals acceleration over time. (F=a/t) Therefore an increase in time equals a decrease in power.
F = ma, not a/t.

Quote
I haven't heard this before... do you have actual physics behind this, or did you think of it yourself? It seems to make sense at first, but then I don't think there is a way to change the direction of momentum. I'd be very interested to know what's going on if that's how it works.
I theorized it myself, but it is based off what Dan Edwards said about a proper roll.  He said your body should automatically fall over when you roll, or something along those lines.  And you can redirect forces using angles.  Also, when you push down on one side of a wheel what happens?  It spins.

Oops haha on the F=ma thing. My bad.  ;)

As for the angles, you need to apply a force in a direction at an angle. Momentum can't really be transferred, (i.e. the decrease in vertical momentum does not correlate in any way to the increase in horizontal momentum), which is what you were saying. Rather, you use force from your legs to redirect your momentum, so that you can fall into a roll, at which point your back absorbs the rest of the impact.
So the important part isn't the change of direction of momentum, it's the force applied that changes the direction of the momentum.

Wheels are pretty complicated, it seems. I have no idea what forces redirect the momentum. Tension, possibly?
« Last Edit: February 09, 2009, 02:58:58 PM by Frank Judge »
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Offline Shamas

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Re: Drop question
« Reply #15 on: February 09, 2009, 08:30:11 PM »
Oddly enough this is a simple question with complex answers....I love it.
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Offline Shane Warren

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Re: Drop question
« Reply #16 on: February 14, 2009, 06:40:58 PM »
lol i just got a physics lesson thanks for the input
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