Calculator Inputs
Enter magnet, conductor, motion, and air values. Use the coupling factor to match real geometry.
Formula used
The calculator estimates magnetic pressure, eddy response, air drag, and air lift. It then combines the terms.
Effective magnetic field: B_eff = B × e^(-g / L)
Magnetic pressure: p = B_eff² / (2μ₀)
Reference force: F_ref = p × A × k
Eddy response: E = tanh((σ / σ_cu) × (t / 0.005) × (v / v_s))
Magnetic drag: F_md = F_ref × E × 1 / √(1 + (v / v_s)²)
Magnetic lift: F_ml = F_ref × E × (v / v_s) / √(1 + (v / v_s)²)
Air drag and lift: F = 0.5 × ρ × v² × C × A
Here, μ₀ is magnetic permeability of free space. The factor k adjusts field geometry and pole coverage.
How to use this calculator
- Enter the magnetic flux density at the magnet face.
- Add the active face area and relative speed.
- Enter the gap and field decay length.
- Set conductivity and thickness for the nearby conductor.
- Adjust coupling and saturation speed if test data exists.
- Enter air values when motion through air matters.
- Press the calculate button and review drag, lift, and net support.
Example data table
| Case | B (T) | Area | Speed | Gap | Conductivity | Use |
|---|---|---|---|---|---|---|
| Small lab magnet | 0.25 | 10 cm² | 1 m/s | 3 mm | 35 MS/m | Class test |
| Brake test rig | 0.55 | 40 cm² | 6 m/s | 5 mm | 35 MS/m | Eddy braking |
| Levitation demo | 0.70 | 65 cm² | 10 m/s | 4 mm | 58 MS/m | Lift estimate |
| Fast rotor check | 0.35 | 25 cm² | 25 m/s | 8 mm | 35 MS/m | Air and eddy force |
Understanding Magnet Drag and Lift
A moving magnet can feel two main force directions. Drag acts against motion. Lift acts normal to the nearby surface. These forces appear when a magnetic field meets a conductor, air, or another magnetic system. The effect is common in magnetic brakes, levitation tracks, falling magnet tests, and sensor rigs.
What the Calculator Models
This calculator uses a practical engineering model. It starts with magnetic pressure. Magnetic pressure depends on the square of the local magnetic field. A stronger field increases force very quickly. The tool then reduces the field for air gap distance. A larger gap weakens the useful field near the conductor.
Eddy Current Response
When a magnet moves near a conductive plate, changing flux drives eddy currents. These currents create fields that oppose the change. At low speed, the force mostly resists motion. At higher speed, the phase changes. Lift can become more visible. Real machines need laboratory data for exact design. This model is best for estimates and comparisons.
Important Inputs
Magnetic flux density is entered in tesla. Area describes the active magnet face. Velocity controls the induced current strength. Gap and decay length control field loss. Conductivity and thickness describe the target plate. Copper has high conductivity. Aluminum is also common. Steel can be harder to model because permeability and saturation matter.
Air Force Terms
Magnets moving through air also experience ordinary fluid forces. The calculator includes air density, drag coefficient, and lift coefficient. These terms are useful for fast moving magnets, rotors, wind tunnel tests, and projectile style studies. For slow table experiments, air force may be much smaller than eddy current force.
Formula Meaning
Magnetic pressure is estimated as B² divided by two times μ₀. The effective field uses an exponential gap correction. Eddy response uses a smooth saturation factor. This avoids unrealistic growth at very high speed. The final drag and lift combine magnetic and air components.
Using Results Safely
The result gives newtons, pound-force, and kilogram-force. It also shows magnetic pressure, effective field, and net support after magnet weight. Treat the answer as a planning value. Exact force depends on magnet grade, pole shape, plate edges, temperature, and nearby metal. Use measured coefficients after testing. Small experiments can improve every input.
Design Insight
Change one input at a time. Watch how force responds. Increasing field or area has a strong effect. Increasing gap usually reduces force sharply. Conductivity and thickness matter until the eddy response saturates. This helps compare designs before building prototypes. Record units carefully before comparing different test cases. Save notes for later calibration work.
Practical Limits
This method is not a full finite element simulation. It does not solve detailed field geometry. It assumes a clean face area and a simple nearby conductor. It is still useful for education, sizing, and early design studies. Check critical systems with qualified tests before final use.
FAQs
1. What is magnetic drag?
Magnetic drag is the force that opposes motion when a magnet moves near a conductor or through a medium. Eddy currents often create this resistance.
2. What is magnetic lift?
Magnetic lift is the force acting normal to a nearby surface. In moving conductor systems, eddy currents can create an upward or separating force.
3. Why does the calculator use magnetic pressure?
Magnetic pressure gives a practical force estimate from flux density and area. It helps convert field strength into a useful reference force.
4. Why does gap distance matter?
Magnetic fields usually weaken with distance. A larger gap lowers the effective field near the conductor, so drag and lift usually decrease.
5. What does the coupling factor mean?
The coupling factor corrects the model for pole shape, edge leakage, alignment, and coverage. Use measured data to tune this value.
6. Can this calculator model steel plates?
It can give a rough estimate, but steel is complex. Permeability, saturation, hysteresis, and shape may strongly change the real force.
7. Why include air drag and air lift?
Fast magnets, rotors, and moving test bodies can have measurable air forces. These are added to the magnetic force terms.
8. What is saturation velocity?
Saturation velocity controls when eddy response starts leveling off. It prevents force from increasing without limit in this simplified model.
9. Is the result exact?
No. It is an engineering estimate. Exact values require geometry, field maps, material properties, thermal effects, and test measurements.
10. Which units are supported?
The form supports metric and common imperial inputs. Results appear in newtons, pound-force, kilogram-force, and watts for drag power.
11. How should I verify the output?
Compare results with a scale, force sensor, or controlled drop test. Always validate calculator estimates with measured test data locally.