This paper investigates the consensus problems for networks of dynamic agents. The agent dynamics is adopted as a typical point mass model based on the Newton's law. The average-consensus problem is proposed for such class of networks, which includes two aspects, the agreement of the states of the agents, and the convergence to zero of the speeds of the agents. A linear consensus protocol for such networks is established for solving such a consensus problem that includes two parts, a local speed feedback controller and the interactions from the finite neighbors. The convergence analysis is proved and the protocol performance is discussed as well. The simulation results are presented that are consistent with our theoretical results.