Weightlifting mathematically

[chocchillimango]

Weightlifting female physicist?

Moons, you are my new best friend

I'm off to see if I can defy gravity a bit this afternoon lol

 

[0ni]

mass remains constant so yes, if the rate of change in velocity (ie acceleration).

However, the rate of acceleration due to gravity on earth does not change so weight is relatively constant.

I'm not sure how terminal velocity is even relevant to this discussion.

The wikipedia article on g-force states quite clearly that:
Weight = -mass x (g-force acceleration)
and that:
The g-force (with g from gravitational) associated with an object is its acceleration relative to free-fall

 

[chocchillimango]

The wikipedia article on g-force states quite clearly that:
Weight = -mass x (g-force acceleration)
and that:
The g-force (with g from gravitational) associated with an object is its acceleration relative to free-fall

that's what I said... acceleration and yes, in free fall.

 

[0ni]

So if the acceleration of an object is less than that of free fall, it's weight is less

 

[Goosey]

mass remains constant so yes, if the rate of change in velocity (ie acceleration).

However, the rate of acceleration due to gravity on earth does not change so weight is relatively constant.

I'm not sure how terminal velocity is even relevant to this discussion.

Succinct

 

[chocchillimango]

So if the acceleration of an object is less than that of free fall, it's weight is less

I think you might be a bit confused.
Let's use a deadlift as an example, on the descent assuming it's done slowly.

The rate at which the bar travels downwards is obviously less than in freefall.
This is NOT because gravity is lower. The rate of acceleration due to gravity is constant, therefore the weight of the bar is constant.

the fact you've failed to consider is that there is a guy/gal holding the bar. The force of the bar's weight is constant because both its mass and rate of acceleration DUE TO GRAVITY have remained unchanged.

Slowing down its descent is exerting a force upwards to counteract gravity. There is an opposing force acting UPWARDS.

If you simply drop the bar, it will be in freefall (setting aside air resistance etc for the moment as small therefore not contributing substantially).
It cannot reach terminal velocity in the distance it will travel.

This is all really basic classical mechanics.

 

[0ni]

Deadlift is a bad example because it is a slow lift
What about in the snatch, it is explosively thrown upwards

 

[Goosey]

Get on a scale and weigh yourself
Now jump up and down on the scale and see what happens to the numbers
This is the simplest analogy I can think of

Now push a loaded bar over your head, first push slowly and controlled, watch the scale.

Now try it againn and push as quickly as possible and see the difference.

 

[0ni]

Now push a loaded bar over your head, first push slowly and controlled, watch the scale.

Now try it againn and push as quickly as possible and see the difference.

The weight shown would increase... due to the fact that force against it has increased.

 

[Goosey]

The other factor which is slowing the bar is friction.

 

[0ni]

The other factor which is slowing the bar is friction.

pls don't make this even more complicated

 

[rino60]

Oni, you are unfortunately mistaken, my friend.

*physicist clears her throat*

Force = mass x acceleration.

"force of gravity" is a rubbish term. What you really mean is that

Weight is a force.
What we love to call "g" is actually the gravitational acceleration on our good earth.
Towit ... Weight (a force) = mass x gravitational acceleration

The acceleration due to gravity,g, as measured on earth is essentially constant to within a number of decimal places.
As such, we generally treat it as a constant.

Oni, I'm afraid the guys are right. Your explanation is both incorrect and unclear.

hope this helps

PS you have confused the matter by talking about spinning on a roundabout. This is not longer a matter simply of linear motion, but introduces the concept of angular momentum.

I love you.

 

[Darkoz]

Weightlifting female physicist?

This deserves another quote and bump
ChocChilli, I am in awe and very impressed!

And Oni, go free fall without a parachute.

 

[Darkoz]

pls don't make this even more complicated

Oh the irony of this statement coming from you Oni!

 

[chocchillimango]

Deadlift is a bad example because it is a slow lift
What about in the snatch, it is explosively thrown upwards

same diff.
the person lifting is exerting a force upwards that exceeds the force of the weight of the bar. The weight of the bar never changes unless you add or remove plates

@Little Hammer ... friction? Unless you're rubbing the bar against something on the way up or down, unlikely.

@Rino60 and Darkoz .. lol my pleasure

 

[callan]

same diff.
the person lifting is exerting a force upwards that exceeds the force of the weight of the bar. The weight of the bar never changes unless you add or remove plates

@Little Hammer ... friction? Unless you're rubbing the bar against something on the way up or down, unlikely.

@Rino60 and Darkoz .. lol my pleasure

the bar in a deadlift should be in contact with the shins and thighs at all times.

not 100% sure on the oly lifts but the bar should be close

 

[Goosey]

Everything has friction callen

 

[trofius]

friction would be negligable, we all know that the magic talc eliminates that.

I guess....

if you applied a force to a bar that was just sufficient enought to move the bar upwards slowly as in a deadlift, the relative weight of the bar would be close to its mass

(ie a set of scales beneth the lifters feet would not increase much,)

if you applied heaps more than just enought power (such as a power clean), to a bar to not only get it moving upwards, but to also cause it to accelerate you could create momentum, or inertia on the bar, this inertia would cause the bar to travel past the point at which the lifter stopped pulling, obviously the heavier the bar the less relative inertia would be created..

here if the lifter was on some scales the weight would read heapes more during the pull stage, and then almost nothing as the lifter dropped under the bar.

if you did a clean with an unloaded bar, you would be able to throw thatbar past your head and possibly into the ceiling, How much power would you be aplying once the bar leaves your hand but continues upward.??

It should possibly also be noted that on the return of the bar not only is there the force aplied by gravity , but also the downward inertia created by it mass at speed, so in a power clean the weight you catch will be more than the mass of the bar.This could also be demonstrated by the lifter standing on some scales.

It kinda comes back to the other argument, about deadlifts and oly lifts, a similar amount of power will move twice the weight half as fast..

But I think in the opening topic it was refering to an object in flight? such as thowing a stone horizontally, were the acceleration applied by the thower causing inertia exceeds gravities ability to pull that stone back to earth, weightlessness?? Eventually drag, caused by the air and gravity will over come the inertia its relative weight will increase again, and it will fall to the earth.

 

[bull]

I hate that the terms inertia and momentum are used interchangably. It may be correct to do so but I hate it. imo inertia should apply to bodies at rest and momentum should apply to bodies in motion.

 

[NAPARM]

the bar in a deadlift should be in contact with the shins and thighs at all times

Says who? Yes you should keep the bar close to your body but your statement is incorrect imo.