Can We Measure Deceleration in Weightlifting Without Specialized Equipment?

[Dale]

Aaa, but no one here can show me one of these experiments ?

Sure we can, these experiments are performed every day in introductory physics labs across the world. You can probably do them yourself. Here are a few examples:

http://sdsu-physics.org/physics_lab/p182A_labs/indi_labs/Newtons2ndLaw.pdf
http://swift.sonoma.edu/education/Newton/Newton_2/html/Newton2.html
http://galileo.phys.virginia.edu/outreach/8thgradesol/Newtons2Frm.htm
http://webpages.charter.net/rhutchis/Physics/Unit5/Lab_Newtons_2nd.pdf

The first recorded experimental confirmation of Newton's 2nd law was by Galileo in his famous "ramp and ball" experiment:

http://en.wikipedia.org/wiki/Experiment#Galileo_Galilei

 

[Dale]

The faster produces more heat.

Agreed. I have never claimed that there is a relationship between heat and impulse, so the relationship is your idea. What do you believe is the relationship and how did you come to that?

The faster moves the weight 6 times further in the same time frame, if you are correct, why does not your slow rep move the weight the same distance, if the impulse is the same ?

Why should it? Again, this is your claim, not mine.

Here is how I see it, let’s just say you are holding the weight, as you also say this exerts the same impulse as me, even thou I am moving the weight for the same time frame, you hold the weight and you exert 80 pounds of force for 1 second, I also at first before the test starts, exert 80 pounds to hold the weight, so far all is equal, however to accelerate the weight I have to use more and more force, my maximum force is a 100 pounds, so I use a 100 pounds of force for one second, and move the weight say 1m, what you seem to do and say, is that when I am on the acceleration my impulse is say 100, but when I am on the deceleration, I am using less force than the weight, so you take 20 off, leaving a impulse of 80, just like you holding the weight. But as I said before, you cannot take anything from my acceleration, it’s all ready been used, and when I am on the deceleration, I am still using force, so basically you HAVE to add on to my accelerating impulse, do you see my point ?

I am not taking anything away. In the first second we each exert 80 lb*s. In the second second you exert 100 lb*s for a total of 180 lb*s and I exert 80 lb*s for a total of 160 lb*s. Then (assuming that in the 3rd second you bring your weight to rest and I keep mine at rest) in the third second you exert 40 lb*s for a total of 240 lb*s and I exert 80 lb*s for a total of 240 lb*s. Impulse is never taken away, it simply accumulates. The 180 lb*s that you exerted in the first two seconds is simply added to the impulse that you exerted in the third second, you merely add less that third second.

Also, don't forget that impulse is a vector quantity. So a negative impulse doesn't mean impulse is taken away, just that it is added in the opposite direction.

I Acceleration is directly proportional to force because, when the mass is constant, so the more force I use moving the weight, the more acceleration, thus more impulse, as of Newton's second law states, F=ma, so if we find value of acceleration then formula will become, F/m=a that is a=f/m this indicates that it is directly proportional.

Interesting that you choose to quote Newton's second law at me when you seem to disbelieve it above. If you accept Newton's second law then my claims regarding impulse follow. If not, then it is rather disingenuous to use it here.

Do you accept Newton's second law?

I use more energy/calories, if the impulse was the same, we both should use the same energy/calories, as we do not, why ?

Why should we use the same calories for the same impulse? These are different quantitties. I have never claimed that there is a relationship, that is your claim. Can you justify that claim in any way?

Odd, now you are saying I am right, well the above is all I am saying, so how and why do you say I am wrong in the other instances ?

10 N*s is obviously greater than 5 N*s and 10 N*s is obviously equal to 10 N*s. The problem is that you cannot yet correctly calculate the number of N*s over a rep, so you think that they are unequal when they are equal.

As that’s what I am doing in the repping, using more Ns thus more impulse ?

Nope. At least, not unless your reps consist of throwing the weights across the gym.

But you too have to decelerate and use less force than the weight ? If I moved a weight 20 inch in .6 of a second, why can I not decelerate and bring it to a complete stop very fast

You certainly can. And the faster you bring it to a stop the more your upwards force is reduced and the smaller impulse it contributes.

Take 5 cars driving into a wall

Irrelevant scenario. Start a new thread.

However you actually have not answered why the fast uses more energy, you have and are are very clever and just say the energy does not depend only on the impulse, but you still can not say why the fast uses more energy.

A human becomes less efficient at faster speeds. I believe that I have stated this clearly and explicitly multiple times in the previous thread.

as do not you agree, there must be a physics answer to the fast using more energy,

I do not agree. I believe that there must be a biology answer, but I don't believe that there is a physics answer (except insofar as biologists use physics in their answer).

It does use more power, its transferring more energy faster because its moving the weight faster, and what do you need to accelerate the weight faster, more force/strength/impulse I say, if not, what ?

Again, this is not a claim that I have ever made. It is only you who is making the claim that more energy implies more impulse. It is a nonsense claim since energy is a scalar and impulse is a vector, but it is your nonsense claim, not mine. If you want to make a nonsense claim then you must be the one who justifies it, not me.

It must, it measures muscle activity, and more activity the higher the reading, and the more muscle activity, means more force/strength/impulse used, what else could it mean ?

Can you derive the relationship between muscle activity and impulse?

However again you have not answered why the fast hits failure faster, you have and are very clever and just say failure time does not depend only on the impulse, but you still can not say why the fast hits failure faster.

This is true, I have not ever said why the fast fails faster. I do not know why. I do, however, know that it is not due to greater impulse, since the impulse is not greater.

I would guess that the answer is more likely related to energy than impulse, but again the question of energy is one of biological efficiency, not physics. You can physically build a machine that does reps as fast as you like without using any significant amount of energy.

 

[waynexk8]

We are still not sure how much both reps deccelerat and for how long ?

Just thought of something else in the equation. With this, we are on the fast reps, moving the weight up 20 inch and down 20 inch x 6 times in 6 seconds. The slow is up 20 inch and down 20 inch x 1 time in 6 seconds.

Also as I said earlier about the forces “on” the muscles not “from” them. Think I wrote that down wrong, it should be when lowering the weight, the force will be lower than the weight, until the transition from negative to positive, then the forces “on” the muscles are higher than the weight of the weight. Unless you say the that forces I lose in the lowering, too which are then made up by the high forces of the transition, are equalled out by the constant forces which are the same as the weight with the slow reps ?

Thus basically as same as the fast and slow concentric. However I still stick to what I said at first, that is the higher forces and impulses and the higher peak forces and impulses of the fast, say 100 and 140 are higher than the constant forces of the slow 80, thus, and this is the main crux of this debate, what I am saying is these peak and higher forces of the fast, are higher and will put more tension on the muscles or more strain on an engine, as you are using the muscles at a 100% capacity, and using the engine at a 100% capacity, thus the using of any system be it biological or machine, will and does put more tension/strain on the muscles/engine, because 100% is a higher force/impulse, and the lower force/impulse can and does not put as much tension/strain on the muscles/engine, proven as you fail 50% faster with the faster reps.

It’s like dropping a 100 pounds on a bridge that has a braking strain of a 100 pounds, if you had two brides the same, dropped 100 pounds on one, the bridge would break, then drop another 100 pounds on the other bridge and that bridge would also break, it’s the same repping very fast, the muscles will tear.

Now you have the same bridges, drop 80 pounds on the bridge and nothing is broke, drop another 80 pounds on the bridge and again nothing is broke, THIS ADDS UP TO MORE THAN THE 100 POUNDS DROPPING, IT ADDS UP TO 160 POUNDS ON PAPER, but still this 160 pounds as NOT done the same damage to the bridge as one drop from the 100 pounds, THIS IS THE SAME WITH THE FASTER REPS, ONE FASTER REP WILL TEAR THE MUSCLES, several slow reps of even higher force/impulse on paper, will and does not put nearly as much TENSION ON THE MUSCLES AS THE FAST REPS, ADD IN SEVERAL FASTER REPS, and you have more impulse faster, it’s like a pneumatic demolition hammer, you can break concrete very easy the higher the beats/bumps per minutes there are, and the higher the Newton’s are each beat/bump.

The other problem with the slow rep is, that at first you have the 3 second positive, with a constant impulse on the muscles, then as the muscles are 40% stronger in the negative, you have 3 seconds to let the muscles sort of recover, with the fast reps there is not time to recover, it’s a constant high force, high impulse, then a very high peak force, very high peak impulse, then and very fast lower force for the negative, the muscles are under a constant very high tension, not like the slow, where the tension is just median all the time.

In other words, the impact force and impulse of the 100, will and does do more damage than the 80, and for the 80 to make up or balance this damage out, it will have to be produced for a far longer time frame. Impulse force with respect to time. When a force is applied to a rigid body it changes the momentum/movement of that body. A small force applied for a long time can produce the same momentum/movement change as a large force applied briefly, because it is the product of the force and the time for which it is applied that is important. But the slow reps do not have a long time, they have the same time as the fast, That’s why the EMG stats higher, you use more energy, and you fail faster with the fast. I do not understand why some think that a 140 and 100 can be make up by 80 ? In basically the same time frame.

Wayne

 

[sophiecentaur]

Oh Wayne.
Are you still here?
When are you going to say something different?
You are running poor old Dale-spam ragged. If you have half the stamina when you're lifting your weights you must be world class.

 

[waynexk8]

Dalepam, will get back as soon as I can. Would like to see the proof on say YouTube, that proves you right in the practical as well, not sure what you meant by that.

Oh Wayne.
Are you still here?
When are you going to say something different?
You are running poor old Dale-spam ragged. If you have half the stamina when you're lifting your weights you must be world class.

I have not come here to mock, but for a serous scientific debate; I know you are a very intelligent person, in your field of intelligence. It's NOT that I have to say anything diffrent, it's you who have first to prove the below in your favor.

So if you want to prove yourself right, you need to say in a scientific way, why I use more energy/calories if as you think both impulses are the same. Then why a very bit of sophisticated computer, to which can add up more and faster than many humans put together states you wrong. Then you need to say why I fail faster in the faster reps.

Wayne

 

[sophiecentaur]

Dalepam, will get back as soon as I can. Would like to see the proof on say YouTube, that proves you right in the practical as well, not sure what you meant by that.



I have not come here to mock, but for a serous scientific debate; I know you are a very intelligent person, in your field of intelligence. It's NOT that I have to say anything diffrent, it's you who have first to prove the below in your favor.

So if you want to prove yourself right, you need to say in a scientific way, why I use more energy/calories if as you think both impulses are the same. Then why a very bit of sophisticated computer, to which can add up more and faster than many humans put together states you wrong. Then you need to say why I fail faster in the faster reps.

Wayne

Not really. I /we are saying that the problem is too basic on the one hand yet too complex on the other. We have been over all this time after time but the definitions of work, force, energy etc etc are all well established. The problem with your request (demand??!) is that the system has just not been characterised properly. Your gizmo tells you about muscle activity and it could be very 'accurate' but muscles aren't springs and motors. They are far too complex and work to their own agenda. The very fact that you get tired just stand holding something tells you that there is no simple answer.
The reason that you fail faster at faster reps is the way that your muscles respire the food. It's nothing to do with the simple mechanics of the situation so you just can't expect an answer in those terms. However many times you come back with this question, the answer will always be the same from PF.
It is possible that a biochemist could give you some answers to some of this but I guess those answers could be above both of our heads. I can guarantee that any full answer to this would be a biological one, so complicated that you are unlikely even to recognise it as the right one.

 

[Dale]

Dalepam, will get back as soon as I can. Would like to see the proof on say YouTube, that proves you right in the practical as well, not sure what you meant by that.

No. I will not do that for you under any rational conditions. YouTube is not a valid scientific resource. If you will not accept the scientific evidence that is in every introductory physics textbook and repeated in introductory physics labs countless times worldwide every semester then you have no business posting questions on Physics Forums.

I need a clear yes/no answer: do you accept Newton's 2nd law as valid here?

Please answer this before responding to any additional posts.

 

[douglis]

So if you want to prove yourself right, you need to say in a scientific way, why I use more energy/calories if as you think both impulses are the same. Then why a very bit of sophisticated computer, to which can add up more and faster than many humans put together states you wrong. Then you need to say why I fail faster in the faster reps.

Wayne

This is total madness!

For God sake...you have the scientific proof and you admitted that you can't understand it!
It's YOUR claims that faster failure and greater energy usage equates greater impulse so it's YOUR job to prove it somehow.
You're obviously unable to do that(that would violate many known laws anyway) so the least thing you should do is to accept the 'authority' and stop bothering us with nonsensical scenarios.

 

[waynexk8]

Let look at the MMMTs, {Momentary Maximum Muscle tensions} the impact/impulse forces of the weight + velocity + distance + time from the transition from negative to positive, these are the highest force that will come from the muscles and will be on the muscles.

The weight will be lowered under control at 2m/s, and just before the transition, the velocity will be at 1.8m/s, we will say the contact/transition {as we are doing equations for a mass dropping and coming into contact with the floor, some little things in my rep transition will have to be change, but here goes my go now} will be for 0.20s and the mass of the weight = 35kg.

What would happen on the every action there is an opposite reaction force/impulse ? 6 balls weighing 35kg are lowered under control at 2m/s {repping the weight up and down, let’s say 1m in .5 of a second this time} into clay, this represents the tension displayed by the muscles, contact with the clay {peak time of tension on the muscles} for 0.20. Then you lower under control, 35kg at .3m/s, do not all agree that the fast = a far far far deeper hole made into the clay than the slow ? This will also be true for the every action there is an opposite reaction force/impulse, when lifting the weights at different velocities, the faster you move the weight up the opposite reaction force/impulse. So lift 80kg up at 2m/s for 6 times, then lift 80kg up at .3m/s for 1 time, contact with the clay {peak time of tension on the muscles} for 0.40, and the opposite reaction force/impulse, “will” be far far far larger for the rep speed of 2m/s.

Fast,
Impulse will = mass x change in velocity/time

{1.8m/s will represent the change in direction}

I = 35kg {2m/s – {-1.8m/s} / 0.20 s

I = 1N.

X this by 2 for the positive and negative = 2N, then x it by 6 for 6 reps = 12N.

Impact force will be roughly 70N.

Slow,
Impulse will = mass x change in velocity/time

{.2m/s will represent the change in direction}

I = 35kg {.3m/s – {-.2m/s} / 0.40 s

I = .25N.
X this by 2 for the positive and negative = .50N.

Impact force will be roughly 10N

So the fast rep in 6 seconds has an impulse of 2300% more than the slow.

Suppose I have done several things wrong there, {however drop 6 balls into a piece of clay like I said 6 times at 2m/s and then drop 1 ball at .3m/s and you will see what I mean about the peak forces from the transition from negative to positive will/are like. then you also have the higher impulse on the muscles for the fast 6 reps up} but at least I am having a go, like a lot have asked me.

Wayne

 

[waynexk8]

I have stated so many times why I think your examples are irrelevant that I'm sure it would be a waste of time to do it once again.But what the hell...

I showed you studies that found that the greater fluctuations of the same average muscle force are more energy demanding.

Where ? Which one was that. HOWEVER that is NOT an answer, the question was “WHY” is more energy/calories used in the faster rep. Please answer my questions directly, and not with answer that have nothing to do with an actual answer to my question.

For example,if the applied force varies from 0 to 10N in a second requires more energy than an applied force that varies from 4 to 6N in a second.Despite the fact that impulse and the average force is identical.

Yes but why, yet again you give no answer, you are basically saying the same question as me, your just say the fast uses more energy in the same time frame, I know that, look in a nutritionist or kinology book and it will tell you that, and why. What I ask is why the faster uses more energy.

That's the ONLY reason that fast reps lead to failure faster.They're more energy demanding(due to their greater fluctuations of force) even though their average force per second is identical with slow reps.

If it was because of greater fluctuations of force, than as these forces are you say average out over the same time frame, then fluctuations of force, must have nothing to do with it. And yet again, you did not actually say why you think greater/more or/and different amounts of fluctuations of force need to use more energy ?

Your example proves that you didn't even read or you didn't understand(most probably) the assumptions that DaleSpam is talking about.

Let me rephrase, you hit a Snooker ball {move a weight as in repping it up}with a force of 10N, the cue {arm/hand/muscles} comes in contact with the ball {weight} for .1 of a second, it moves 1m {arm moves the weight up 1M} hits another Snooker ball, {the weight goes full ROM, and that jolt goes on the muscles as tension} the original Snooker ball stops, and the second Snooker ball goes 1m. You hit a Snooker ball with a force of 5N, the cue comes in contact with the ball for .1 of a second, it moves 1m hits another Snooker ball, the original Snooker ball stops, and the second Snooker ball goes 500mm. This will be the same as your muscles moving a weight, as the reaction, reaction, will then be the muscles moving the weight, and the reaction, reaction from the force and impulse will be the tension on the muscles.

All you did above is again get out of answering the question, how can you say that a force of 5N is equal to 10N.

We're talking about cases where the load starts and stops at rest hence there's zero change in momentum.

By momentum do you mean movement ? If so there is a change, it’s about 1m

In your example,in the first case the one ball hits the other with double speed than the second case(I assume that the 10N and 5N are average values) and in .1sec the balls stop in both cases.
So the first case has double change in momentum than the second.Nothing like our weight lifting example where the change in momentum is always zero.

Not sure why you say there is no momentum/movement ? Let me show you on the fast, it starts still, then has momentum/movement for 1m then it changes direction and has momentum/movement for 1m, this happens 6 times in 6 seconds, the slow just goes up once and down once in the same time frame.

Please try and think other than you must use more impulse as you fail faster, or something else, it can only be this I think ? If as you think it is more fluctuations of force, then why would that be ? It is because the impulses do not even out at the end ?

Wayne

 

[Dale]

Please answer my question of post 37.

 

[douglis]

If it was because of greater fluctuations of force, than as these forces are you say average out over the same time frame, then fluctuations of force, must have nothing to do with it. And yet again, you did not actually say why you think greater/more or/and different amounts of fluctuations of force need to use more energy ?

The force and the impulse "average out"...not the energy usage.Are you able to understand the difference?
The fact is that fluctuations of the SAME force are more energy demanding.Why?I don't know and I don't care.The answer is irrelevant because is purely biological.
I could search at the discussion page of the studies to see the opinion of the biologists but I won't waste a minute of my life for something irrelevant.

By momentum do you mean movement ? If so there is a change, it’s about 1m

Wayne

Oh God...No...I don't have patience to deal with this!

 

[Dale]

I need a clear yes/no answer: do you accept Newton's 2nd law as valid here?

Hi waynexk8, since your name is crossed out, I assume that you answered this question in the negative and therefore got banned. I am sorry to see that, but if you do not accept basic physics principles like Newton's 2nd law then there is nothing that can or should be done to answer you in terms that you will accept. In fact, with that outlook, I have no idea why you are even bothering to ask your questions on Physics Forums. Any answer you receive here will obviously be based on experimentally validated physical laws like Newton's 2nd.

 

[Dale]

As one final follow-up, let me simply list the take-home messages.

1) Impulse over any number of reps depends only on the weight and the total time, not the speed of the rep.
2) Reps start and stop at rest, the above does not apply to scenarios where the weight does not start and stop at rest.
3) Reps involve only the lifting force and gravity, the above does not apply to scenarios involving another force on the weight.
4) The force from the muscles is always equal and opposite to the force on the muscles.
5) Energy consumption has no unique relationship to impulse.
6) More energy is consumed in the faster rep because the human is less efficient at higher speeds.
7) 6 does not contradict 1 because of 5
8) Fatigue has no unique relationship to impulse.
9) Fatigue occurs sooner in the faster rep for biological reasons (unknown to me).
10) 9 does not contradict 1 because of 8

I think that is a pretty complete characterization of the things I had hoped you would learn.