How to control the weight of an object?

  • #1

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Hello everyone,

First off, i would like to apologize for any spelling errors. I am Portuguese and my english is going to be very simple.
I am in the process of building something and i am reaching out to the physics community for help solving a problem.
I am a CNC programmer and while i was in one of my classes in school (Pneumatics) the teacher spoke to us about the principal behind a "Pneumatic Jack" and an "Air Check Valve".
Basically, the valve makes it possible for a human being to lift a car with just the strength of his arms.
This gave me an idea....and a problem to solve.
How do i control the weight of an object?

I need to be able to choose the weight that the object will have with just the turn of a button.
Think of a sphere....it has a button on the side, it's inicial weight is "2 pounds", but if i turn the button to "5", the weight is now "5 pounds".

I've been looking for maybe an element with expending mass, maybe the combination of two elements, where one affects the composition of the other, causing it's mass to expande, but i also need it to retract to it's original weight with another turn of the button to "2".
.
Maybe something in the fields of magnetic forces or electrical current?
I am neither a physicist nor a chemist so this is just me rambling.

This is a question a leave to you if you'll accept the challenge.
Again, sorry for my english, i hope i got the idea across.

Thank you for your attention, and i would really appreciate any feedback.
Take care.
 

Answers and Replies

  • #2
sophiecentaur
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How do i control the weight of an object?
Hi and welcome to PF.
Basically you can't unless you take it to the Moon or somewhere else with a lower g field. You could do your experiment by pumping water in or out of a container and that would change the load on your jack. A "button" could control the pumping.
 
  • #3
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Or you could attach an elastic rope to the ceiling. Tighten the rope to reduce the weight and loosen the rope to return it to normal.
 
  • #4
jbriggs444
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The usual way of providing a precisely variable force is with a "scale" or "balance".

You place an object whose weight is unknown on a spring scale and the device automatically applies just enough supporting force to keep that object motionless. One then examines the dial or digital readout to determine how much force was applied.

Or you place an object on the platform of a balance and add (or move) the right combination of weights to manually apply just enough supporting force to balance it exactly. One then counts the weights (or their offsets on an arm) to determine how much force was applied. [Or, more precisely, how much mass was balanced].
 
  • #5
berkeman
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  • #6
DaveC426913
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As others have pointed out, there are ways of compensating for weight by
- providing some alternate lifting mechanism (buoyant gas, elastics, electromagnetism, etc.), or
- using mechanical advantage, such as a lever
- moving it to a lower gravity location.

But if you're looking to literally make object X have lower mass, you're out of luck.
 
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  • #7
256bits
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Levers work fine.
A truck balance for example can weigh a truck of several tons, just by moving a small weight on a beam to different positions.

By changing the length of the lever arms, or the position of the fulcrum, you can change the "weight" of the mass at your desire.
Maybe use a rolling fulcrum.

( This didn't post at around 0830 EST so its late Internet jinx )
 
  • #8
sophiecentaur
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This gave me an idea....and a problem to solve.
How do i control the weight of an object?
I'm going to spoil your party here, I'm afraid and ask you "What object and by how much do you want to vary it?" :wink:
 
  • #9
DaveC426913
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I'm going to spoil your party here, I'm afraid and ask you "What object and by how much do you want to vary it?" :wink:
I'm more concerned that he's looking for a way to change the physical property of said object so that it actually masses less, not weighs less - and do so without the use of external weight-reducing mechanics, such as balloons or levers.
 
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  • #10
sophiecentaur
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There has been no feedback from @Nuno Miguel yet. Without it, we are in a vacuum, I think.
 
  • #12
sophiecentaur
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That reply just sucks.
 
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  • #13
jbriggs444
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You could reduce its wait by vacuuming once a day instead of once every five years.

[Pun intended]
 
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  • #14
berkeman
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You could reduce its wait by vacuuming once a day instead of once every five years.
Funny typo making your statement a tautology... :biggrin:
 
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  • #15
davenn
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Funny typo making your statement a tautology... :biggrin:
haha

I didn't even pick that one up
 
  • #16
DaveC426913
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haha
I didn't even pick that one up
:scratches head:
I thought that was the pun. Which is why I thought berk's comment about it seemed redundant.:rolleyes:
 
  • #17
berkeman
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:scratches head:
I thought that was the pun. Which is why I thought berk's comment about it seemed redundant.:rolleyes:
Notice the timestamps on my reply and jbriggs editing his post. Sneaky... :biggrin:
 
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  • #18
davenn
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:scratches head:
I thought that was the pun. Which is why I thought berk's comment about it seemed redundant.:rolleyes:

as berkeman said, you saw it too late

jbriggs has already edited it after he saw berkeman's comment
 
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  • #19
berkeman
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BTW, there's a good way to increase the weight of an object at will.

When the SWAT officer steps on the scale to get his weight recorded every 12 hours during a 48-hour exercise, you can observe one of his "partners" sneaking up behind him and adding his toe to the back of the scale. When done skillfully, this can cause said officer to worry that he will get booted from the exercise for excessive water weight gain or loss. LOL. Not that I've ever been part of a medical team watching this tomfoolery...:biggrin:
 
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jbriggs444
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  • #22
davenn
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LOL. Not that I've ever been part of a medical team watching this tomfoolery...:biggrin:

noooo, of course not, you would never be involved in anything like that :wink::wink::biggrin:
 
  • #23
lekh2003
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This thread has descended into lame puns.
 
  • #24
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If you really want to change the weight of an object simply add or remove mass. My water tank does this by pouring water in at the top, letting it out at the bottom.
 

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