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Hamiltonian mechanics

In Hamiltonian mechanics, we define the Hamiltonian as:

H=T+V.\begin{align} H &= T + V. \tag{1} \end{align}

Which is the total energy of our system. Another difference from Lagrangian mechanics is that we define HH in terms of pip_i and qiq_i instead of qiq_i and q˙i\dot{q}_i. The equations of motion with no non-conservative forces are:

p˙i=−∂H∂qiq˙i=∂H∂pi.\begin{align} \dot{p}_i &= -\dfrac{\partial H}{\partial q_i} \tag{2} \\ \dot{q}_i &= \dfrac{\partial H}{\partial p_i}. \tag{3} \end{align}

Equations (2) and (3) are often called Hamilton's equations. To account for non-conservative forces, we merely add the corresponding generalized force terms to the right-hand side of Equation (2). In other words:

p˙i=−∂H∂qi+Qi.\begin{align} \dot{p}_i &= -\dfrac{\partial H}{\partial q_i} + Q_i. \tag{4} \end{align}

This creates a new kind of space that we can visualize our solution on that has dimensions qiq_i and pip_i. This type of space is known as phase space.