# Electromagnet pull force calculation:

• Dash-IQ
In summary, the conversation discusses a formula for predicting the force of attraction between two objects using electromagnets. This formula is known as Maxwell's force formula and involves taking the gradient of the potential energy. The methodology for using this formula is correct, but for a more accurate result, the Lorentz force equation should be used. The conversation also mentions the skepticism towards online calculators and the need for a practical example to validate the formula. Finally, the conversation touches upon the complexities of physics and how misunderstandings can lead to catastrophic results.
Dash-IQ
I'm trying to predict the possible pull force of some electromagnets from the following equation:

FPull= ( n x I ) 2 μ0$\frac{A}{(2 g ) ^ 2}$

F : Force.
n : Number of turns.
I : Current.
μ0 : permeability of air.
A: Area in m2
g : the gap that is separating the electromagnet and the object.

Maxwell's force formula.
Is this a good way to predict the force of attraction?

Online calculators use this formula as well.

The most straightforward way to predict a force is just to remember that the force is the gradient of the potential :)

gburkhard said:
The most straightforward way to predict a force is just to remember that the force is the gradient of the potential :)

I am not 100% sure about the formula you wrote yourself since I didn't actually do the problem out myself, but the methodology in the link you posted is correct. They do take the gradient of the potential to get the force, which is what you can do for any system, and the maxwell's force formula just applies this to this particular case: (you'll note the step they used, "F = dW/dg Equation FRP"). Here they used W to signify energy and g to signify the distance (g is for gap, but they should've used a different variable since g should be the fixed gap distance, not just a position variable). But anyway, yes, so if you take the energy of the total system and then take the position derivative of the energy and evaluate in the gap, you will get the right answer. However, that is for a simplified system where they assume the field is just constant in the gap. If you want the real answer, you're probably best actually going around the coil and integrating the force on differential current elements in the wires just using the regular lorentz force equation.

gburkhard said:
I am not 100% sure about the formula you wrote yourself since I didn't actually do the problem out myself,

The formula I posted is from the link., not from me.
But, I was highly skeptical of the online calculator until I review that link, and it started to make sense.

I don't usually look at the potential gradient, due to my lack of understanding. But I will re-read the link again to review.

I think something is wrong with it. If this would be true you could lift very big weight with few kilowatts and then you could make an impossible machine outputting megawatts. You could pull a piece of metal with great force would result very high torque and if your velocity is high enough you could make power output several ten times more.
So something must be wrong. Using FEMM outputs somewhat similar but still something must be wrong with it.
Must find a practical example to validate.

This is the problem with physics, mentally ill insanes like John Hagelin (religious extremist hindu terrorist, LG nobel prize winner LOL ) or Einstein publicate relativity (its been known by indians maybe thousands of years ago) and the result is usually catastrophic misunderstanding and inability to calculate the reality.

Very sad how the world is now.

## 1. What is the formula for calculating the pull force of an electromagnet?

The formula for calculating the pull force of an electromagnet is F = (N x I)^2 x μ0 x A^2 / (2 x g^2), where F is the pull force in Newtons, N is the number of turns of wire, I is the current in Amperes, μ0 is the permeability of free space, A is the cross-sectional area of the magnet, and g is the distance between the magnet and the object being pulled.

## 2. How do I determine the number of turns of wire for an electromagnet?

The number of turns of wire for an electromagnet can be determined by the desired pull force and the formula N = √(2 x F x g^2 / μ0 x A^2 x I^2), where N is the number of turns, F is the desired pull force, g is the distance between the magnet and the object being pulled, μ0 is the permeability of free space, A is the cross-sectional area of the magnet, and I is the current in Amperes.

## 3. What is the role of current in calculating the pull force of an electromagnet?

The current in Amperes is a crucial factor in calculating the pull force of an electromagnet. The greater the current, the stronger the magnetic field, resulting in a higher pull force. However, there is a limit to how much current can be applied before the magnet overheats or becomes damaged.

## 4. How does the distance between the magnet and the object being pulled affect the pull force?

The pull force of an electromagnet is inversely proportional to the square of the distance between the magnet and the object being pulled. This means that as the distance increases, the pull force decreases exponentially. It is important to keep this in mind when designing and using electromagnets.

## 5. Can I use the same formula for all types of electromagnets?

No, the formula for calculating the pull force of an electromagnet may differ depending on the type of magnet being used. For example, if the magnet has a core made of a ferromagnetic material, the formula will include a term for the permeability of the core material. It is important to consult the specific formula for the type of electromagnet being used.

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