Derivatives from Conservation Laws

Just like with ordinary differential equations, partial differential equations can be characterized by their order.

The order of an equation is defined by the highest ordered partial derivatives in the equations.

Looking at the equation in question,

The partial derivatives are:

Notice that each partial derivative contains two variables, thus this equation is a second order partial differential equation.

The conservation law written as a partial differential equation is found by applying the divergence theorem to the conservation equation.

The conservation equation is,

Now, recall the divergence theorem which states,

Thus, by substituting

for results in,

From here, rewriting this equation to bring the derivative inside the integral along with substituting

,

and performing some algebraic operations results in,

After integrating over the domain the partial differential equation that is found is,

Just like with ordinary differential equations, partial differential equations can be characterized by their order.

The order of an equation is defined by the highest ordered partial derivatives in the equations.

Looking at the equation in question,

The partial derivatives are:

Notice that one of them partial derivative contains three variables, thus this equation is a third order partial differential equation.

When dealing with partial differential equations, there are phenomenons in the physical world that have specific equations related to them in the mathematical world.

Looking at the possible answer selections below, identify the physical phenomena each represents.

is known as the heat equation.

is known as the wave equation.

is known as the Laplace equation.

is known as the Poisson equation.

is known as the biharmonic wave equation.

Therefore, the correct answer for the biharmonic wave equation is

Just like with ordinary differential equations, partial differential equations can be characterized by their order.

The order of an equation is defined by the highest ordered partial derivatives in the equations.

Looking at the equation in question,

The partial derivatives are:

Notice that one of them partial derivative contains three variables, thus this equation is a third order partial differential equation.