In labs, scientists can measure how thick or sticky liquids are using different methods. There are a few popular ways to do this:

1. Capillary Tube Viscometer

• How It Works: A liquid flows through a narrow tube, and the time it takes for a certain amount of liquid to go through is recorded.
• Dynamic Viscosity Formula: $\mu = \frac{\pi r^4 (P_1 - P_2) t}{8LQ}$ Here, $r$ is the tube's radius, the difference in pressure is $P_1 - P_2$, $t$ is the time it takes, $L$ is the tube's length, and $Q$ is the flow rate.
• Measuring Range: This method can measure dynamic viscosities from about 0.1 mPa·s (like water) to over 1000 mPa·s (like honey).

2. Rotational Viscometer

• How It Works: A spinning rod is placed in the liquid. The force needed to keep it spinning at the same speed is measured.
• Dynamic Viscosity Formula: $\mu = \frac{T}{\omega r^2}$ In this formula, $T$ is the force, $\omega$ is how fast it spins, and $r$ is the radius of the rod.
• Where It’s Used: This tool is great for thick liquids like pastes and plastics, measuring from about 0.1 mPa·s to 100,000 mPa·s.

3. Falling Sphere Viscometer

• How It Works: A small sphere falls through the liquid, and how fast it falls is measured.
• Dynamic Viscosity Formula: $\mu = \frac{2r^2 (\rho_s - \rho_f) g}{9v}$ Here, $r$ is the sphere's radius, $\rho_s$ and $\rho_f$ are the densities of the sphere and liquid, $g$ is gravity, and $v$ is the falling speed.
• Measuring Range: This method is good for liquids that are not too thick, measuring from about 1 mPa·s to 1000 mPa·s.

4. Kinematic Viscosity Measurement

• How It Works: Kinematic viscosity ($\nu$) is measured using tools like the Ostwald or Ubbelohde viscometer. It is found by dividing dynamic viscosity by the liquid's density: $\nu = \frac{\mu}{\rho}$
• Measuring Scale: This is often measured in Stokes (1 St = 1 cm²/s), with common values from 0.01 St (like water) to over 10 St (like oils).

These methods give scientists a detailed way to measure both dynamic and kinematic viscosity, which helps in understanding different types of liquids and their properties in the lab.