GRAVITY DOES NOT PULL YOU FORWARD!!!!!!!!!!

IB wrote:

Wow you guys are idiots, gravity does pull straight down in effect (which isn't exactly true, but I rather not go there), but with the application of proper body mechanic it will pull you forward, because of your inability to factor in the multiply event which make up the physics of running and your inability to apply basic logic you guy who said gravity doesn't pull you forward made complete idiots out of your self congrats.

I'd say your writing in the above paragraph does more to prove you misunderstanding of gravity than anything I can write.

Once again, a force that acts only directly down (ie gravity) can not pull you in any direction that has a horizontal component (ie forward).

For ANY forward motion to occur, there must be the application of a force in the opposite direction. In running, this is the force applied by your feet in a backwards direction against the friction between your shoes and the ground (and why you run a heck of a lot slower when you are slipping on ice).

From reading this thread, it looks like the Intelligent Designers have been beaten to the punch of re-writing high school science in the US.

According to Newtons third law every action has an equal and opposite reaction. In the case of gravity Fnormal is the counteraction force that prevents objects from being pulled twords the center of the earth. Fnormal always pionts perpendicular to the surface on which the object lies. Now Fgravity always pulls twords the center of the earth. On a slant uphill or down hill the Fnormal and Fgravity are not pionted in the exact opposite direction that is they do not ballance eachother. That means there is an unbalanced force in a horitzontal drection when you are running on a slant. Running down hill this force is litterally pulling you foward so gravity is in a way pulling you foward. It has to because there are no unballanced forces in nature

JimFiore wrote:

As far as the 45 degree question is concerned, if you ignore the effect of air friction the issue boils down to the extra work your muscles would have to do to keep you in a specific position, plus any effects on your biomechanics such as limiting your range of motion.(velocity, incline, wind, etc.)

Let me first say, Jim, that you have done a tremendous job defending your position about the work that gravity can do in the horizontal direction for someone running on a flat plane, which is zero to very acceptable approximations.

However, there is no work done in keeping something in a certain position. So your muscles do not do any work to "keep you in a specific position." For example, when pushing on a large object, you have done no work until that object actually changes position.

7th grade physics teacher wrote:

wait... you aren't isaac after all. you're FIG newton! i knew it!!

i see you aren't able to refute anything i've said. you are weak. stick to lecturing 12 year olds.

marijuologist = Doctor Stupid

dkjsghsdjkgh wrote:

you are wrong, also. an object without momentum CAN impart a force. its called inertia. for every reaction there is an equal and opposite rection. there for, if you are trying to push said 300 pound man, his body is pushing back (imparting a force) in order to resist motion.

no, you are wrong. not only wrong but ignorant. all inertia is is the resistance a body has to a change in its momentum. and inertia is proportional to the mass part of the formula P=mv for momentum.

a 300 pound man has the same inertia whether he is standing still or running. furthermore it makes no difference whether the 300 pound man is standing still and something pushes him, or if the 300 pound man and someone else collide. either way the 300 pound man has a RELATIVE MOMENTUM to whatever is pushing him.

so i say again, no object can impart a force if it has no momentum. if an object has no momentum that pertains to all objects that are relative to it that have 0 relative velocity. the instant you start talking about some other object acting on the 300 pound man you are giving the man a relative momentum.

now piss off

gotcha! wrote:

marijuologist = Doctor Stupid

What is with the marijuologist obsession in all of my threads? So what if I am Doctor Stupid? Your point would be...?

lets surmise what we know so far:

marijuologist = iflyboats = Doctor Stupid = 75% of the personalities on this board

I didn't admit to being Doctor Stupid. You inferred as much.

JimFiore wrote:

As far as the 45 degree question is concerned, if you ignore the effect of air friction the issue boils down to the extra work your muscles would have to do to keep you in a specific position, plus any effects on your biomechanics such as limiting your range of motion. If you held your torso at 45 degrees, it seems to me that you be expending extra energy to do so versus being more or less vertical (that is, there's a greater torque). I suspect that some deviation from perfect vertical may be in order depending on individual biomechanics and other factors (velocity, incline, wind, etc.)

I probably shouldn't have used such an extreme angle as an example. I was really just trying to ask whether having your center of gravity shifted in the direction that you're running (i.e., forward), which would seem to result from even a slight forward lean, would be make for more efficient running than if you were to shift your center of gravity to the rear, which would seem to result from leaning backward.

Intuitively, it seems to me that shifting the center of gravity forward would be more efficient, which makes me think a slight foward lean also would be more efficient than a perfectly upright posture, as long as the lean isn't so extreme that it requires excessive work by the quadriceps and other large muscles just to keep you from falling on your face.

I think most posters here have made a fundamental error interpretating the purpose(and importance) of using a phrase like "Gravity pulls you forward". It is not intended to give runners a physics lesson (Newtonian or otherwise), it is intended as a mental framework to give runners a feel for the optimal running action.

There are many explanations and cues given in sports that are plain biomechanically or physiologically wrong but they work! It is critical to provide simple clues that match the intuitive understanding of the athlete. We all know that intuition is unscientific but working against the way somebody perceives the world is generally doomed to failure.

It's all about being fit for purpose - something that can be very useful on the sporting field would be unfit in the lecture theatre and vice versa. That's why some people are effective coaches and others are obsessive lab rats desperately pressing message board buttons in hopes of a reward.

You make good points, but can't people give "cues" without saying things that are blatantly incorrect?

It is technically correct. As with the upside down pendulum, gravity can "pull" the center of mass forward with respect to an initial position. Obviously this requires reaction forces from the surface, but the initial force is gravity.

It is a useful concept to think about when promoting footstrike directly under or behind the center of mass instead of in front. In front means a deceleration due to gravity (at that instant) directly over gives no force and slightly behind gives a slight acceleration (at that instant).

Now you're talking about center of mass...not center of gravity. They're two different things. GRAVITY IS ONLY A VERTICAL FORCE. CLOSE THIS THREAD.

a miler wrote:

It is technically correct. As with the upside down pendulum, gravity can "pull" the center of mass forward with respect to an initial position. Obviously this requires reaction forces from the surface, but the initial force is gravity.

It is a useful concept to think about when promoting footstrike directly under or behind the center of mass instead of in front. In front means a deceleration due to gravity (at that instant) directly over gives no force and slightly behind gives a slight acceleration (at that instant).

a miler wrote:

It is technically correct. As with the upside down pendulum, gravity can "pull" the center of mass forward with respect to an initial position. Obviously this requires reaction forces from the surface, but the initial force is gravity.

It is a useful concept to think about when promoting footstrike directly under or behind the center of mass instead of in front. In front means a deceleration due to gravity (at that instant) directly over gives no force and slightly behind gives a slight acceleration (at that instant).

Sorry wrong again. Gravity is not doing work in the "forward" direction because the force of gravity is perpendicular to that direction. When people think about pendulums and levers, many neglect to consider the force that the pivot point or the fulcrum exerts on the object. The pendulum is no different. Whatever the top of the pendulum is attached to exerts a force through the rope onto the object, which causes it to move in the forward direction.

In the runner's case, the pivot point is the foot, and the force at that pivot point is the foot's friction with the ground, which propels the runner forward, not gravity.

I didn't say doing work. I said move forward. There is a difference. After all, the concept of physics work is not entirely applicable in the real world. If you push against an immovable ojbect, in the physics sense you are doing no work, but it sure as hell doesn't feel that way.

Yes, it is only the reaction force that, in a proper physics diagram can be considering in the horizontal direction. However, this reaction force exists because of the force of gravity acting as a torque on the arm of the pendulum, as you put it.

Basically this is all a bunch of nitpicking about technicalities and various interpretations of definitions.

Given the innaccuracies posted on this thread, I find it completely implausible that humans actually invented the atomic bomb and landed a man on the moon. Both must have been pure luck.

even if you were pushing against a solid brick wall you are still doing work. the work is happening on the microscopic scale of your muscles.

The only reason people are "nitpicking" is because THERE IS NO INTERPRETATION of the LAW of gravity as it is being discussed here. There can't be. Science will not allow a different definition of gravity for every situation.

a miler wrote:

Basically this is all a bunch of nitpicking about technicalities and various interpretations of definitions.