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Force, mass versus resistance to move a weight

  1. Jan 8, 2012 #1
    I have my own theory on this, but first would like to ask the forum. And the members answering on my other thread, this question is separate but needs to be answered first. Also I have started answering that one.

    If use lift 80% of your 1RM, repetition maximum, why is it easier on a barbell than lifting the same weight if it was in a solid lump, however please this solid limp has handles just like the barbell, and its “not” at all awkward to pick up. Please take any/all of the awkwardness out of this question please.

    As I notice on many things that seem to have their mass in a different position easier to pick up, and FAR FAR FAR more easy than you might think, let me try and explain.

    Let’s say I can lift 350 pounds on the bench press, first I put on the 50 pound bar, 5 plates at 30 pounds each, on each side of the bar, each of the 10 plates is 1inch thick and 12 inch diameter, the lift is VERY hard.

    Second I put on the 50 pound bar, just one plate of 150 pounds each side at 2 inch thick and 30 inch diameter, the lift “IS MORE” easy than the first lift, but the weight lifted is the same.

    This ACTUALLY does happen to me and everyone else in real life who lifts weight, and the above was an exaggeration, as if I put any kind of bigger plates on in diameter, as to more plates on that have more mass and thickness in whole, the lift with the bigger plates is always more noticeable harder to pick up.

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  3. Jan 8, 2012 #2

    Simon Bridge

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    It's the lever action of your muscles on your bones, and which muscles you bring to bear.
    Try the same motion without the weight - one of them is easier than the other.
  4. Jan 8, 2012 #3
    I believe he is saying the same lift, same weight, just a different configuration. I would guess that it has to do with the more motion available to more plates, these plates shifting a little bit makes you work muscles to balance them, with just one plate on each side there is less motion?
  5. Jan 8, 2012 #4

    Simon Bridge

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    Oh, I should have added: stability. Another use for leverage and so on.
    It's more work to hold something above your head (say) than by your waist.
    Weights farther apart is easier than close together.

    Lots of heavy disks on each end of the bar distribute the weight over more of the bar-length than just a few big disks - even though they are the same weight. Have you tried putting the big weights at the center of where the little ones would have run? How about pulling the big plates right in to just outside where your hands go?

    The farther apart the center of masses of the weights, the more stable. What happens is the large moment of inertia resists the ideomotor effect so your muscles have to work less to do so.

    Of course, if it's so heavy the bar is bending then wobbles in the bar can throw all this off.

    Human musculature is complicated, and there are usually a lot of different effects combining in even quite simple movements.
  6. Jan 9, 2012 #5
    I believe that's the answer.The little shifting of the big plates creates small torques that activate secondary muscles and the motion becomes harder.
    That's also the reason why free weights are always harder compared with weight lifting machines with strict motion.

    BTW what's your own theory OP?
    Last edited: Jan 9, 2012
  7. Jan 9, 2012 #6
    I suspect human psychology might play a factor. I lift weights and can't say I have ever felt the effect that OP is describing. However, if I was convinced of this effect then I suspect that I would feel it.

    I don't see how you can reliably measure this effect to remove all doubt, either. Depending on what day it is/ temperature/ barometric pressure I feel stronger or weaker. Back-to-back testing is also unreliable as you'll be a little bit weaker on the second test. Either way, I propose blindfolding the tester and asking him what configuration the plates are in. Many times. I'm guessing he won't be able to tell.
  8. Jan 9, 2012 #7
    If you hold the barbell at different widths, say with 3 inch gap and then a 25 inch gap, in say the barbell in the bench press, {think all should know the lift the bench press} of many other lifts, that you will be “FAR” stronger in the 25 inch, as of the lever action of your muscles on your bones, and several other things.

    But this happens when your hands are in the exact same place, on all exersices.

  9. Jan 9, 2012 #8
    No, as I know use a smith machine, it’s the type of machine where you can have say nothing on one side and a 25 pound plate on the other, and it still goes up and down finish, with no unbalance. Also on this machine AND on a barbell, there is no movement in the weights, as they are held of tight with collars, so all is balanced fine.

    Last edited by a moderator: Sep 25, 2014
  10. Jan 9, 2012 #9
    Hmm, as I said above, this happened on free weights, as I noticed this over thirty years ago, but now I use a smith machine, and like the barbell the weight are locked very tightly on, there is no movement at all.

  11. Jan 9, 2012 #10
    Perhaps the difference is in your mind. I lift free weights 3 times a week and I can see no difference when using 45 lb plates or smaller weights (that add up to the same total). This applies to many repetition sets as well as 1RM attempts. If you're comparing the smith machine to free lifting (bench), it will feel much lighter on the smith machine, as the standard bar olympic bar weighs 45 pounds and the smith machines bar does not.
  12. Jan 9, 2012 #11
    Great points, here I will give what I think makes this happen, but first I need to tell you exactly what I did yesterday, for you all to comment on my opinion.

    It was triceps day, and the exercises was close grip bench press, {this exercise has no value to this effect, this effect happens on all exercises} holding and lifting the bar with a 11 inch wide grip, I was too lazy to take the smaller plates off and put the big ones on, well to cut a long story I found this first lift quite hard, and I was on my first set or 6 repetitions for 6 sets, adding weight to each set.

    So after just 3 reps I put the weight down and pulled off the small plates and put on the bigger ones, the starting weight was not that heavy, but after changing the plates I noted the weights went up far easier, as I have always noticed when putting on bigger plates. D. you might be able to try this.

    Here is my theory,
    Looking from above, the small plates will look like a Triangle, 13 inch the big side, chamfering down to 8 inches, and the distance from the large side of the Triangle to the small is 3.5 inch.

    Looking again from the top at the large plate, this will just be an Oblong from above, 16.5 by 1.2.

    The only thing I can think of, is that the big plates has far more mass then the smaller plates, so it’s easier to push up a smaller mass with the same weight, into the air resistance and the force of gravity, well the answer is yes, BUT I would never of thought I would notice this with such low speed and short distance. I know at first you may think, no can’t be, but if I exaggerate this, and say 12 plate on the 35 pound bar, this makes it more difficult again, measurements if that was on the bar, looking from above an Oblong 13.5 by 8.5 mass.

    We all know about aerodynamics; however with this weight I would only be moving it 22 inch up in 1 second. But something is making it easier.


  13. Jan 9, 2012 #12
    Hi there,

    I have noticed this on barbell for the last 30 years, and other things you try and lift in live that have the same weight but far more mass. As I have not had the smith machine long.

    What’s your best bench press, or say 90% or 80%, next time go into the gym, warm up, and put just 5 or 10 pound plates on the bar till it adds to your total, try the lift. Then have at least 10 minutes, put the biggest plates you can find, and then try.

  14. Jan 9, 2012 #13
    Wayne, i'm not doubting your experience or credability.

    I am offering that it could be a psychological difference that is to blame for the apparent difference in weight. When I workout tomorrow (Tuesday) I will use different combinations of weights when I do free-bench (as you have suggested). I will then report back. I have done so in the past and notice no difference, but it never hurts to try again.

    I agree with you that using the proper clips and collars wobbles and wiggles within the plates can be diminished and mostly eliminated. I don't feel that air resistance plays a large roll in the lift as it is done rather slowly. I also do not see how two items could have the same mass but different weight when placed in the same gravitational potential, maybe I misunderstood your post. So my best guess is still it's psychological... If I were forced to give another answer (involving physics) I would say that the aformentioned theory which states that movement within the plates causes torque to be applied is to blame, as well as uncertainty. It is possible that weights are made with a level of uncertainty (maybe + or - 0.5 lbs). If using a 45 pound plate this could net only 0.5 extra pounds. However when using 4 10 pound plates, or 8 (4 on each side) this could add as much as 4 pounds. This hypothesis could be directly tested by using a scale to measure your weights (or using a balance).

    Please clarify one thing for me before I attempt to replicate your results.. Have you noticed this increased diffuculty only when lifting close to the 1 RM, or at other weights as well?

    If you would like to talk more about gym and fitness related things, you can email me. My email address is the same as my forum username, at gmail dot com.
  15. Jan 9, 2012 #14
    Yes that’s fine, no problem. Just to say I am 50 and have lifted from say 12.

    Ok thx. Just stack a load on small plates on, and just clean and press, then put one very big plate on, you should find 55s or 100s in a Gym.

    Yes it’s totally eliminated.

    I actually lift quite fast, explosively, or try to lift say 80% for say 10 reps as fast as possible, first you can you heaver weight then lifting very slow, second I claim as of this and many threads, and as you use more energy, fail faster, move the weight more distance and my EMG reading state this, that you use more overall or total force lifting the same weights in the same time frame but, I move the weights as fast as they will go, ok maybe not all the time as its far too hard.

    So what would be the air resistance on a 40 pound DB moved thought the air 20 inch up and 20 inch down for 30 reps ??? Can that be worked out.

    As we all know that if you somehow had a Yard square steel plate with a handle on the bottom, and forget about wobble or balance, as that would be far harder as of going against air and the force of gravity to move up and down 20 times to moving the same weight on a barbell. But do just a few plates made a noticeable difference like I notice.

    Well I don’t think they have a direct mass, but they do have a different mass going though the air, as if you look at the dimensions of the weights I put above, as its only the plates going though the air, at the thinnest part, if you see what I mean.

    Well you never know, but I am not that sort of person.

    Hmm, could not we test this some other way ???

    Yes that’s a possibility; however I have noticed this for many years, and in many different lifting situations.

    Please clarify one thing for me before I attempt to replicate your results.. Have you noticed this increased diffuculty only when lifting close to the 1 RM, or at other weights as well?

    If you would like to talk more about gym and fitness related things, you can email me. My email address is the same as my forum username, at gmail dot com.[/QUOTE]

    No, I have noticed this on doing 10RMs.

    I first noticed this when I was about 14. We used to have 112 pound bags of cement {yes I know this is different as it a bit clumsy to lift, and in the middle is the weight} I knew at that age I could press ??? Think it was 130 pounds, not exactly sure, so I tried to lift the cement bag, but could not press it, was quite mad, as being that age and all, later that day, I stacked the same weight on the barbell, but in the middle, I could press this, but it was far far far harder than with the weights on both sides. Several months later I bought some new plates, they were 50 pounds each, my old were 25 pound each, I put these new weights on the bar for the first time, and I noticed this weight go up much easier that with 2 25 pounds on each side, and I could do more reps.

  16. Jan 10, 2012 #15

    Simon Bridge

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    There is a confusion here ... "weight", in physics and engineering, is a technical term which means the force of gravity on a mass.

    The mass is the resistance to changes in movement.

    But commonly "a weight" is a metal disk with some mass printed on it. At the surface of the Earth there is a constant ratio between the mass and the weight - so we commonly print the mass (kgs lbs whatever) of those disks of metal on them. We would commonly refer to the mass written on the weight as "the weight". Which can get confusing.

    What makes you think that two objects with the same weight can have different masses?
    The only way this happens is if there are different strength gravitational fields, or if the mass written on the weight is wrong.

    I had a look at the video, the use of a smith machine would remove the moment of inertia effects I was talking about before ... that would have been important information. It is easy to understand why free lifting would be tougher with fewer bigger weights ... not so clear with this one.

    I'd have to see it to be sure of what is happening in your exact case.
    Usually, when someone reports something like this, it turns out to be a psychological effect - easily verified even with a blind test. But there is sometimes an additional effect ...

    when you train you usually start with lighter weights and move up to the heavier ones - as you warm up. If you started with the heaviest you'd strain something and the weight would feel heavier than when you build up to it.

    This should give you a clue.
    When you climb back to move the weights around you get a small relaxation as well.
    Normally you move back to increase the weight so you expect the next lift to get harder anyway. You are usually humming from the exercize so you wouldn't normally describe this as relaxing :) I'm using the word in the technical sense of coming out from being under tension.

    Have you ever tried lifting the other way around? Remove the small weights, lift the heavy ones as the next step up for a bit. Then swap out for the smaller plates same mass again?

    You should get the same effect, only now it is the smaller weights that feel heavier.
    (I'm not saying this is what happens with you, it's just a common effect.)

    There is another possibility to do with the torque you and the weights put on the bit that holds the bar to the frame ... this will depend on how the weights are mounted in the machine which is why I'd have to see it. You'll find if you pull on the bar as well as lift, the bar is harder to move ... especially if the machine hasn't been greased recently. There may be an extra twist when the weight on the ends of the bar is all in one place.

    Now given all that - there is another possibility: especially if others report this effect on the same equipment. Maybe the small weights are a little light? You probably wouldn't notice the discrepancy with just one, but when there are lots of them together you may notice it.

    So the first thing to test is the weights - weigh the stack of small disks against the "same" weight of big ones. Ideally you want this done on the smith machine - which would mean rigging up a pulley.

    That is the only way that the two sets of weights can have different masses.
  17. Jan 10, 2012 #16
    There's no such thing as "a smaller mass with the same weight".Two objects with the same weight always have the same mass.

    The air resistance is less than negligible...not even worth talking about it.

    I guess the psychological factor is the answer here.I tested myself yesterday and didn't notice any diference by changing the plates.
  18. Jan 10, 2012 #17
    There's no such thing as "a smaller mass with the same weight" Cool, no density...he didn't say lesser mass.
  19. Jan 10, 2012 #18
    O.K. I mispoke:smile:.But I guess all his plates are made of iron!
  20. Jan 10, 2012 #19
    I was seeing the weight on the bar, and my Triangles and Oblongs, as Mass, and the more smaller weights on the bar {please see above, my Triangles and Oblongs} the more mass as mass is a measure of how much matter an object has, however I meant area.

    Ok sorry maybe I was saying it wrong, I meant the bar with the more plates on has a bigger area going up, so a bigger area going up against gravity and air resistance, would be harder than the less plates with less area going up. We all agree that right, but would this be big enough to justify my experience ???

    As let’s say I am moving say 90% on the squat of bench press, I can really fell a difference on the next set with the bigger plates on, “and” if I have gone up 10 pounds.

    My mistake as I said should have said area, as lead and steel. Or the different areas in the above weightlifting example.

    It does happen basically the same of free weights, however, if you are doing a lift different from the bench press, hope/think all know that lift, that’s not straight up, like say the curl, below. Then the weight will spin on the bar as you can see in this video, and lucky in this video I found on the internet, you can really see the plates spin, so more smaller plates would make this exercise harder, but the bench press and the squat the two I notice it on, are not like this exercise the curl, but just up down.


    Well you could be right, it could be psychological, but I just got a feeling its more bigger area moving up against gravity and air resistance, and when I put the big plates on, it’s just quite a big difference, very noticeable. If it was psychological, I would have thought that more smaller plates make the bar look heavier, or there again the big plates could make it seem psychological also. However I am 50 and train on my own, and are trying to impress, not sure if you did mean that.

    JUST thought of this, lifting lots of smaller plates on the bar just feels heaver are it’s a sort of dead weight, you know when you try to lift someone from the floor, and your surprised at how heaver or hard it is, and you sort of say, yes your heaver as you’re a dead weight, mind you that a little different, as its just more awkward to pick up a person than a barbell.

    Well I always have a warm up of 60% for 12 reps, but your right you can say do 8 reps of 8 sets and add weight each time, or you can just keep the weight the same and have less time in-between sets, there are so many different ways.

    I can do warm up, then put leave the small plates on and add many more, do the work set, say immediately to myself, that was harder than I thought, {and in this stage in my lift, it would only be two pound heavier than my last training session} I should have pulled all the small ones off and put the big ones on from the start, so I then do, then also the weight will be about 10 pounds heavier than the last time, and it still feels easier to move.

    Yes I did try this, and changing from one or two very big plates to many small plates feels harder.

    You should get the same effect, only now it is the smaller weights that feel heavier.

    Yes you are very right there, if you look at the curl video above, and if you do, as I have done a few time, put the collars on, that’s the ends that hold the weights on, if you put them up as tight as you can against the plates and then tighten them, the plates will not spin at all, and the weight to curl can by VERY hard to curl this way, until you try it you will not believe how hard it is, as you must not have them like that, the plates have to spin around, as seen in the video.

    Ok will try that. So you don’t thing that these big plates and the more of the smaller plates, with more area going up against gravity and air resistance could be it ??? Hope you all get what I mean now on the smaller plates having more area, and remember there are two sides to the barbell, so the two sides will have to bigger areas going up against gravity and air resistance, please see my writings on the areas and dimentions on them above.

  21. Jan 10, 2012 #20
    Bit late here, will repply to the other posts again, and the other thread.

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