Speed or acceleration

[fx]

I couldn't find any old topics about this, though I'm sure it's been discussed. Does what this guy say have any merit?

Anyway, it is obvious that what a vaulter must over come is gravity or acceleration. So, it would stand to reason that it is extremely important for a vaulter to be accelerating through the last step of the vault while jumping off the ground. Now, here is the tricky part (at least for me). There is a trade off. The faster a vaulter is running (higher speed or large momentum) the slower the acceleration or small force and v/v.

So, what vaulters do or at least what coaches attempt to get their vaulters to do is to NOT reach maximum speed so that one can accelerate not decelerte through the vault.

So what should I, as a coach, be trying to get my vaulter to do. Which is more important speed or acceleration, momentum or force. Is there possibly a magic ratio. Is it possible that a slower vaulter could obtain a greater acceleration and have the potential of vaulting higher.

I see so many vaulters, some even world class that appear to only be striving to reach a top speed and maintain that speed through the vault. But, it looks to me like even though speed is obviously important that the emphasis should be more on the acceleration???

Any thoughts or comments would be greatly appreciated. Even if you do not understand the vault, you can relate it to a couple of cars in a head on collision (actually, this would be much much simpler to discuss). We could discuss one car travel at an extremely high speed and the other traveling at a fast speed but a higher acceleration. Who wins, where is the "magic" number or calculation here?

Thanks
Nautica

from http://www.physicsforums.com/showthread.php?t=58782

[VaultMarq26]

I understand what he is saying with the speed vs. acceleration. It actually makes alot of sense, but you have to take it with a grain of salt......you can be accelerating 10mph at take-off if you are only doing a 3-step approach, but only traveling 12mph. You could also be accelerating 5mph at takeoff, but be traveling 17mph.

What he is asking about is the ratio. As far as I see, you want to be going as fast as possible at take-off, and this is accomplished by continually accelerating throughout the approach.

That is what I get from it. I don't know how you can determine the optimal numbers, or if it would even be worth it.

[dougb]

Make the last two steps as quick as possible. Throw in the after burner.

[lonestar]

Isn't the entire approach an acceleration? Can you even reach "maximum" speed in a 30-40m approach run? Can you reach "maximum controllable speed" while still accelerating at takeoff?

[VaultMarq26]

It is a relative maximum speed.....if your top speed is 23mph, you will not be able to run 23mph with a pole in your hand.

Many athletes reach thier top speed 30-40m because they are not able to accelerate for 60m like many Olympic sprinters.

You bring up a great point about Maximum Controllable speed. I know that I personally don't run as fast as I can down the runway because I can't controll myself if I do.

[HHSPVCoach]

Ok, there is a difference between Force and Energy. You want to create as much Energy as possible (for reasons I'll show in a second here) not necessarily create a great Force.

From high school level physics we can see that Force = mass x acceleration (or deceleration). But the greatest force would be created when you have maximum acceleration (or decel) which would mean coming to a velocity of zero. But we are not doing this in the vault, we are continuing through. Anyway, force is not what we want to be looking at, it's energy.

From Newtons laws (I can't tell ya which one) we know that energy cannot be created or destroyed, just changed forms. In the case of the vault we are dealing with two types of energy, kinetic and potentional.

Kinetic energy is the energy of motion, defined as KE = 1/2 * mass * velocity^2. (that's squared.) Potential energy is stored energy and when applied to the vault is how much energy something has at a height, i.e. PE = mass * gravity * height.

Now since Newton says that we cannot create or destroy energy, we know that in the system of a vault that Kinetic Energy will equal Potential energy, so doing a little math (hope everyone can understand the abbreviations.)

KE = PE, thus
1/2*m*v^2 = m*g*h
Now, lets remove the constant on both sides, mass:
1/2*v^2 = g*h
Now we remove the constants (the 1/2 and the g, which we cannot change)and make this a proportion;
v^2 = h (that should be a squiggly equals, meaning "is proportional to")

Therefore, we can say that velocity is directly related to height, in other words, if you run faster, you will vault higher!!! (This, of course, assumes a perfect vault and perfect conversion of energy.) So, what i'm saying is that acceleration is not as important as the fact that you are at your maximum speed at the moment of takeoff!

Ok, my brain hurts a little now, I suppose I should get back to work.

See you all on the track,
Coach Phil, BSME

[VaultMarq26]

I understand and agree with what you are saying, but I think that the idea of accelerating through the take-off helps prevent deceleration. Few athletes can hold their max speed for great distances. In most 100m dashes, the last 20-30 meters is a fight to hold off deceleration.

Basically if a vaulter runs from a mark of 100' and takes off at 13', but he hits his top speed 20' into the approach, he will have decelerated by the time he takes off the ground.

Most, if not all, higher level vaulters implement this in thier approach.

[HHSPVCoach]

I agree completely. That is why a properly structured runup is so very important. I see quite often high school kids running 8, 9, or even 10 left runs and they've hit their max speed 3 or 4 lefts into it. If they ask me for help the first thing I do is shorten their run and then start working on how to properly pace it. Making sure that the last few steps are an acceleration up to their max possible (controllable) speed.

[stavhoppare]

IT IS FAR BETTER FOR THE ATHLETE TO BE ACCELERATING THROUGH THE TAKE OFF AT 95% SPEED THAN DECELERATING THROUGH AT 95% SPEED. WHEN IN THE ACCELERATION MODE, THE JUMPERS' STRIDE PATTERN AND BODY POSITION ARE CORRECT TO PROMOTE PROPER JUMPING MECHANICS. WHEN DECELERATING, THE ATHLETE IS STRIDING OUT, LEANING BACK, AND CANNOT UTILIZE PROPER JUMP MECHANICS

[pvmike20]

ideally you want to reach your maximum controlable velocity at the instant you takeoff. If you simplify the vault down to a basic kinematic equation your velecity at take of is the only varible.

[taliek]

Is it better to arrive at take off at 9.53 m/s decelerating or 9.26 m/s accelerating ? (for exemple)

I guess 9.53 !

[VaultMarq26]

I would disagree....in general, if you are decelerating, you will not be able to set up a proper take-off....the idea of accelerating is to properly position your body for take-off