Relationship between split time and stroke rate

[MartinSH4321]

When you row at the same pace at higher SPM you stroke must be weaker.

Your example:
When you row with 200W at 20 SPM every stroke has an energy of 600 joule.
With 200W at 30 SPM every stroke has an energy of 400 joule.

One WattMinute is 60 Joule

[JotaBg]

All clear now, guys, thanks

I was confusing Power with Energy/Force applied to the handle. Since W = J/s it makes sense that the stroke rate does not influence it.

At a lower stroke rate, more energy will be required if we want to keep a given pace constant.

Many thanks to you all!

J

[jamesg]

The erg with it's air-braked flywheel is an interesting lesson in physics and Newtonian dynamics, with difficult ideas such as action and reaction being equal and opposite, Work, Power, inertia, torque, ISO units, speed, the equivalence of gravity and acceleration.. Have fun, it's like going back to school. C2 have even put in the idea of Pace: the time it takes to go an arbitrary distance on a machine that does not move..

[Allan Olesen]

The question is: how can it be that they complete that given distance at the same time? Wouldn't Rower B finish first since he applied the same power (202.5W) 30 times per minute vs 20?

Here, you are confusing power with energy.

Power is energy divided by time. Or energy is power multiplied by time.

Both Rower A and Rower B produce a power of 202.5 W. If they do that for 1 minute (60 seconds), they produce an energy of 202.5*60 = 12150 Joule.

Rower A used 20 strokes to produce those 12150 Joule, so he produced 607.5 Joule per stroke.

Rower B used 30 strokes to produce those 12150 Joule, so he produced 405 Joule per stroke.

So rower A used fewer strokes per minute with more energy per stroke. Which result in the same total energy over one minute, and consequently the same power.

Edit: I guess I should have read all the new posts before replying. You have already figured it out yourself. But I will let this stay, in case any other new members can learn from it.

[JotaBg]

Thanks guys, this is very helpful

@Allan: I had already figured it out, but it always helps seeing it written so clearly. Thanks again

J

[JotaBg]

Hello guys,

I have an additional question and I didn't want to start a new post only for it, so hopefully you can help me out with it here.

Does anyone know how the instant measure of Power (Watts) that the PM monitor shows in each stroke is actually calculated by the Ergometer? Since Power = Energy / time, does it calculate the energy that we put into the handle (based on flywheel acceleration) and divides it by the time that it takes to take that stroke?

I am aware that other machines use an average power of the last three strokes and that's what is shown on the monitor, but don't know if that's the case for the Concept2 as well

Thanks!
J

[jamesg]

The PM sees the flywheel speeds at start and end of the idle recovery phase, during which only air brake torque acts on the flywheel. Using these speeds, flywheel inertia and stroke times, PM calculates the average rate of Work done by the flywheel on the atmosphere; which is the power we supply.

[JotaBg]

Thanks Jamesg, this clarifies a lot

This means that stroke rate indeed affects the Wattage readout of the machine, which makes sense based on all the previous posts. If we keep the energy that we apply to the handle constant, a higher stroke rate will result in a higher power output (and therefore a lower split rate)

[Citroen]

This means that stroke rate indeed affects the Wattage readout of the machine

No it does not. Simple physics: work = force * distance. The ergo is slightly different because there's a spinning flywheel (so we have to change to things like angular momemtum).
http://eodg.atm.ox.ac.uk/user/dudhia/ro ... l#section4

[JotaBg]

No it does not. Simple physics: work = force * distance. The ergo is slightly different because there's a spinning flywheel (so we have to change to things like angular momemtum).
http://eodg.atm.ox.ac.uk/user/dudhia/ro ... l#section4

There's something that I don't understand then.

Based on your comment, two rowers pulling with the same energy would have the same Power (Wattage) regardless of the SPM.
So if one is applying a given amount of energy at the handle (in Newtons) 20 times per minute (20 SPM) and the other is applying the same amount of energy in N 30 times per minute (30 SPM), you are saying that both monitors readouts would be the same in terms of Watts/Split time and therefore it would take them the same time to complete a given distance?

There must be something that I am missing here...

[hjs]

No it does not. Simple physics: work = force * distance. The ergo is slightly different because there's a spinning flywheel (so we have to change to things like angular momemtum).
http://eodg.atm.ox.ac.uk/user/dudhia/ro ... l#section4

There's something that I don't understand then.

Based on your comment, two rowers pulling with the same energy would have the same Power (Wattage) regardless of the SPM.
So if one is applying a given amount of energy at the handle (in Newtons) 20 times per minute (20 SPM) and the other is applying the same amount of energy in N 30 times per minute (30 SPM), you are saying that both monitors readouts would be the same in terms of Watts/Split time and therefore it would take them the same time to complete a given distance?

There must be something that I am missing here...

You think energy per stroke. Citroen thinks energy nomatter what strokerate.

Ofcourse if you pull more strokes with the same energy per stroke, the more strokes, the faster you go.

[Citroen]

a given amount of FORCE at the handle (in Newtons) 20 times per minute (20 SPM) and the other is applying the same amount of FORCE in N 30 times per minute (30 SPM),

FTFY, you're welcome.

Energy is the result of distance * FORCE.

[JotaBg]

Thanks both

Sorry for not using the right units, I have a weak background in physics

So, as a conclusion, my understanding is that a similar force per stroke will produce a higher power (per stroke) readout at a higher stroke rate

I tried it this morning. A few strokes at a 20 spm applying a certain force and a few strokes applying more or less the same force but in this case at a 12 spm approx. Even though I applied a similar force, the wattage per stroke was much lower when the spm were reduced. Does this make sense?

[hjs]

Thanks both

Sorry for not using the right units, I have a weak background in physics

So, as a conclusion, my understanding is that a similar force per stroke will produce a higher power (per stroke) readout at a higher stroke rate

I tried it this morning. A few strokes at a 20 spm applying a certain force and a few strokes applying more or less the same force but in this case at a 12 spm approx. Even though I applied a similar force, the wattage per stroke was much lower when the spm were reduced. Does this make sense?

100%

[Citroen]

Thanks both

Sorry for not using the right units, I have a weak background in physics

So, as a conclusion, my understanding is that a similar force per stroke will produce a higher power (per stroke) readout at a higher stroke rate

I tried it this morning. A few strokes at a 20 spm applying a certain force and a few strokes applying more or less the same force but in this case at a 12 spm approx. Even though I applied a similar force, the wattage per stroke was much lower when the spm were reduced. Does this make sense?

I don't think your experiment worked. If you apply the same force over the same stroke length then you get the same number of indicated watts, because you can't change the laws of physics. You may get better results attempting to compare 20spm with 25spm or 30spm (as long as the shortened recovery time for 30spm doesn't ruin your results).