In physics, curvilinear density is a measure of the mass of an object distributed along a curve. It is defined as the mass per unit length of the curve. The SI unit of curvilinear density is kilograms per meter (kg/m).

Curvilinear density is often used to describe the mass of objects that are thin and long, such as wires or rods. It can also be used to describe the mass of objects that are distributed along a curved surface, such as the shell of a sphere.

The formula for curvilinear density is:

```

ρ = m/L

```

where:

* ρ is the curvilinear density (kg/m)

* m is the mass of the object (kg)

* L is the length of the curve (m)

For example, consider a wire that is 1 meter long and has a mass of 10 grams. The curvilinear density of the wire is:

```

ρ = m/L = 10 g / 1 m = 0.01 kg/m

```

This means that there is 0.01 kilograms of mass per meter of the wire.