**Answer:**

The SI unit of viscosity is the pascal-second (Pa·s).

**Explanation:**

It is possible to measure the viscosity of fluid since it is a measure of its resistance to flow.

The viscosity of a liquid is commonly referred to as its “thickness” in the scientific community.

For example, we say that honey is “thicker” (has a higher viscosity) than water since it is thicker than the latter.

Viscosity can be measured by placing a fluid between two flat parallel plates and sliding one plate past the other, as shown below.

In terms of the above diagram, the formula for viscosity η is

```
``` η=FδAv

Thus, the units of viscosity are N×mm2×m⋅s-1=N⋅s⋅m-2=Pa⋅s.

If a fluid is placed between two 1 m2 plates that are 1 m apart and one plate is pushed sideways with a force of 1 N and it moves at a velocity of 1lm⋅s-1, then the fluid has a viscosity η=1 Pa⋅s.

Many chemists still use an old unit of viscosity, the **poise** (P), named after the French physician Jean Poiseuille.

It is a convenient unit because 1 mPa⋅s=1 cP.

For example, the viscosity of water at 20 °C is 1.002 mPa⋅s or 1.002 cP.

Honey has a viscosity of about 10 Pa⋅s or 10 000 cP.

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