Visualization
Calculator
Pick a method, enter inputs, and compute the sedimentation coefficient. Required fields are marked *.
Example data table
These sample rows show typical inputs and the resulting coefficient in seconds and S units.
| Case | Method | v (m/s) | RPM | r (m) | s (s) | s (S) | |
|---|---|---|---|---|---|---|---|
| A | Velocity | 2.0e-6 | 45000 | 0.070 | 1.006e-13 | 1.006 | |
| B | Velocity | 3.5e-6 | 55000 | 0.065 | 1.716e-13 | 1.716 | |
| C | Buoyancy | 1.2e-19 | 1.1e-11 | 1000 | 7.3e-4 | 7.636e-13 | 7.636 |
Formula used
How to use this calculator
- Choose a method: velocity-based for measured boundary speed, or buoyancy-based for material parameters.
- Enter required inputs using consistent SI units (m, s, kg, and kg/m³).
- Click Calculate. Your result appears above the form, just under the header.
- Use Download CSV for spreadsheets, or Download PDF for printing and sharing.
- Compare S values across samples to infer size, shape, and assembly state.
What the coefficient represents
Sedimentation coefficient s links radial motion to centrifugal acceleration and reflects size, shape, and hydration. In velocity form, s = v/(ω²r). If ω doubles, ω² rises fourfold and s drops 75% when v is unchanged. The unit is time; 1 Svedberg (1 S) equals 10⁻¹³ s, keeping values readable. Higher s generally indicates faster sedimentation under identical solvent and temperature conditions.
Typical ranges and scale
Many soluble proteins fall near 2–20 S, while large ribonucleoprotein complexes often exceed 50 S. A 10 S species corresponds to 1.0×10⁻¹² s. If your result is 0.2 S (2.0×10⁻¹⁴ s), re-check units: r must be meters, and v must be m/s. Also confirm that v is radial, not tangential stage motion.
Uncertainty propagation
The velocity method is sensitive to ω and r because they appear in the denominator as ω²r. A 2% RPM error becomes about a 4% ω² error, shifting s by roughly 4%. A 1 mm radius error at r = 70 mm is ~1.4% and directly changes s by the same proportion. When averaging frames, report the time window used.
Velocity workflow checkpoints
Use measured boundary speed v in m/s and boundary radius r in meters. At 45,000 RPM, ω ≈ 4,712 rad/s. With v = 2.0×10⁻⁶ m/s and r = 0.070 m, s ≈ 1.01×10⁻¹³ s, or about 1.01 S, matching the example table. At 55,000 RPM with v = 3.5×10⁻⁶ m/s and r = 0.065 m, s is about 1.72 S.
Buoyancy workflow checkpoints
In buoyancy form, s = m(1 − ρv̄)/f, where (1 − ρv̄) captures buoyant mass reduction. For ρ ≈ 1000 kg/m³ and v̄ ≈ 7.3×10⁻⁴ m³/kg, (1 − ρv̄) ≈ 0.27. With m = 1.2×10⁻¹⁹ kg and f = 1.1×10⁻¹¹ N·s/m, s ≈ 7.6×10⁻¹³ s (7.6 S).
Reporting and comparison
Report s in seconds and S, and record temperature, solvent composition, and the method because viscosity and density shift results. Use CSV exports to compare replicates; for example, three runs at 9.8, 10.1, and 10.0 S average to 9.97 S with 0.15 S spread. PDFs are best for sign-off and sharing. If you publish, state rotor type, speed, and r reference.
FAQs
What does a larger S value usually imply?
Under the same solvent and temperature, a larger S typically indicates faster sedimentation, often due to greater mass or a more compact shape. Compare only under matched experimental conditions.
Why can my result be negative?
Negative s commonly occurs when v is negative due to direction choice, or when (1 − ρv̄) becomes negative in the buoyancy method. Re-check signs, units, and whether the particle is less dense than solvent.
Should I enter radius in centimeters?
No. Enter r in meters to match SI units in the formula. If you have centimeters, divide by 100 before entering. Unit mistakes can change s by orders of magnitude.
Do I need RPM or angular velocity?
Either works. If you enter RPM, the calculator converts it to ω using ω = 2π·RPM/60. If you already know ω in rad/s, select the ω option and enter it directly.
What friction coefficient f should I use?
Use the translational friction coefficient appropriate to your particle and solvent, often derived from hydrodynamic models or experimental diffusion/viscosity data. Ensure units are N·s/m for consistency.
How should I report the final value?
Report s in S and seconds, plus temperature, solvent composition, rotor speed, and the radius reference. If averaging replicates, include mean and spread, and keep significant figures consistent with measurement precision.