Calculate Magnet Strength for Lifting 75 kg Iron in 1 Second - Morten

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Discussion Overview

The discussion revolves around calculating the strength of a magnet required to lift a 75 kg mass of iron vertically by 1 meter in 1 second. Participants explore the factors influencing this calculation, including the shape of the magnet and iron, as well as the airgap between them.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant asserts that the strength of the magnet cannot be calculated straightforwardly, as it depends on the shapes of the iron and magnet, particularly the airgap, suggesting possible answers could range from 1T to 100T.
  • Another participant introduces the concept of magnetic energy density in the airgap and provides equations for energy and force, questioning whether the airgap is 1 meter or if the magnet and iron are in contact.
  • A further contribution suggests calculating the required magnetic field strength (B) and the H-field needed, proposing a specific area for the calculations and deriving values based on given parameters.
  • One participant mentions needing approximately 216,000 ampere-windings for a distance of 1 meter, considering two airgaps.

Areas of Agreement / Disagreement

Participants express differing views on the calculation's feasibility and the factors that influence the magnet's strength, indicating that multiple competing perspectives remain without a consensus on a definitive answer.

Contextual Notes

The discussion highlights limitations in assumptions regarding the shapes of the magnet and iron, the airgap's dimensions, and the specific conditions under which the calculations are made.

Ankhen
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Hi. Can somebody make a calculation for me?
how strong do a magnet need to be to lift a mass of 75 kg iron 1 meter straigth up in 1 second.
Best Regards morten
 
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Ankhen said:
how strong do a magnet need to be to lift a mass of 75 kg iron 1 meter straigth up in 1 second.
It cannot be calculated just like that, because it depends on the shape of the iron and the magnet ( actually the shape of the airgap ).

So correct answers could be 1T or 100T, depending on the shapes.
 
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Hesch said:
It cannot be calculated just like that, because it depends on the shape of the iron and the magnet ( actually the shape of the airgap ).

So correct answers could be 1T or 100T, depending on the shapes.
Hi Hesch and thanks
Can you explaine it a little more, perhapse with some calculations so I can understand it?
 
Ankhen said:
Can you explaine it a little more
The attraction is not due to some "magnetic poles" inside the magnet, but due to magnetic energy density in the airgap between magnet and iron, which is:

Edens = ½*B*H [ J/m3 ].

Thus the energy: E = Edens*(volume of airgap) = Edens*(cross section area)*(width) of airgap = Edens*A*s.

The force: F = dE/ds = Edens*A.

Is the width of the airgap 1m in the starting position, or are magnet/iron closed up all the way ?
 
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Hesch said:
The attraction is not due to some "magnetic poles" inside the magnet, but due to magnetic energy density in the airgap between magnet and iron, which is:

Edens = ½*B*H [ J/m3 ].

Thus the energy: E = Edens*(volume of airgap) = Edens*(cross section area)*(width) of airgap = Edens*A*s.

The force: F = dE/ds = Edens*A.

Is the width of the airgap 1m in the starting position, or are magnet/iron closed up all the way ?

Can you calculate it with both airgap 1m and with the magnet/iron closed up.
It would really be a big help.
Do you have a email or facebook I can contact you? It seems like you know you way around this stuff,and I have some psysics-questions i prefer not to ask in a open forum
 
Ankhen said:
Can you calculate it with both airgap 1m and with the magnet/iron closed up.
Say that the total area, A = 0.1m2, then

Fdens = m*g / A = 7370 N/m2 →

Edens = ½*B*H = 7370 [ J/m3 ] →

B*H = B2 / μ0 = 14730 [ J/m3 ] → B = 0.136 T.

Now, if s = 1m, try to calculate the H-field needed ( B = μ0 * H ). Then calculate the amount of ampere-windings needed using Amperes law:

∫circulationH⋅ds = N * I.

You should use a ∩-shaped magnet.
 
Hesch said:
Then calculate the amount of ampere-windings needed
PS: You will need about 216000 ampere-windings by a distance = 1m ( × 2 airgaps ).
 

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