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Weightlifting mathematically

Wouldn't the weight stay the same? as gravity is the same.

Wouldn't speed just increase force?

Wouldn't mass would stay the same as the particle matter is the same in the object being moved faster?

 
I get the analogy Oni, but its not correct.

If I stand on scales and jump, the scales read less. I still weigh the same though.
 
callan said:
weight stays the same, just a greater force is applied to it
Click to expand...

the weight of an object is the force on the object (Richard C. Morrison (1999). "Weight and gravity - the need for consistent definitions")
 
weight is related to how hard gravity is pulling you against the planets surface.

Go stand on a bigger or denser planet, you may struggle to stay upright, the scales would indicate that you are muchmuch heavier... Your mass however has remained constant.
 
All this has nothing to do with lifting a weight so I'll ask again Oni, you said the weight will decrease with speed, so I'm asking how does the weight get lighter as you lift it faster?
 
Darkoz said:
All this has nothing to do with lifting a weight so I'll ask again Oni, you said the weight will decrease with speed, so I'm asking how does the weight get lighter as you lift it faster?
Click to expand...
this, the weight remains the same all the time because the force of gravity never changes, but the force you apply to the weight exceeds the of gravity allowing it to come off the floor, but the weight is still the same no matter what.
 
Darkoz said:
All this has nothing to do with lifting a weight so I'll ask again Oni, you said the weight will decrease with speed, so I'm asking how does the weight get lighter as you lift it faster?
Click to expand...

The weight does not get 'lighter' as you lift it faster, and the argument put forth (which is getting more convoluted and less correct) is not only a poor analogy of how weight works, but also incorrect. The force that you exhibit on a set of scales (which at rest is purely m*G) is your weight. Jumping up and down does not decrease or increase your weight, but increases the force that is exhibited as a result of the velocity and direction of movement of the mass. This change in force is not a change in weight of the object, but purely a positive or negative force which changed the apparent weight that you must move.

With respect to the lifts, it doesn't change the weight of the barbell, but does change the force required to move/stop it.
 
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Gravity is not the only force that comes into play when you lift a weight. There is also the force applied to the bar. You need to apply less force to the bar as the bar speeds up to maintain speed and applying max force the whole time would increase bar speed. It goes without saying that the weight decreases as the force needed to be applied decreases and they are both proportional to one another. If the force on the bar is more than the force gravity applies, the net force is upwards
 

Weight of an object = the force on the object
This is a fact
If the force required is less, the weight is less
 
0ni said:
Weight of an object = the force on the object
This is a fact
If the force required is less, the weight is less
Click to expand...
so a 5kg stone that is thrown at the floor isnt 5kg when it hits the floor?
 
Sticky said:
How is the force less?
Click to expand...

The force needed to be placed on the bar is less if the bar is already moving.
Weight = mass * gravitational force
When something is moving at speed, it takes less to keep it moving at the same speed (I can't explain this very well at all sorry lol). Like pushing a car, getting it started is the hardest part, but when it is moving you are applying less force to it to maintain that speed.

Think of a band assisted deadlift, at the top, you will have 200kg in total including the bar, but it will feel (it's weight) less than 200kg because the force of the bands upwards against the bands is making the force of gravity less. And weight = mass * gravitational force
 
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