Mechanical Engineering - Engineering Mechanics - Discussion

The total momentum of a system of masses in any direction remains constant unless acted upon by an external force in any (that) direction.

Momentum will change if we apply force in any direction.

According to principle of energy conservation, energy can't be created can't be destroyed. The definition not belongs to the statement.

For the momentum we need mass and the movement of the mass so it is the phenomenon which deals with the moving mass interaction and also a continuous change which can never be constant. Because momentum = mass *ds/dt and ds/dt term is a continuous change of displacement with respect to time.

The statement is newton's second law not law of conservation of energy.

Principle of conservation of energy states that energy can neither be created nor be destroyed.

This should be like this only, the total momentum of a system of masses in any direction remains constant unless acted upon by an external force in any (that) direction.

Momentum will change if we apply force in any direction.

The law of conservation of energy, first formulated in the nineteenth century, is a law of physics. It states that the total amount of energy in an isolated system remains constant over time. The total energy is said to be conserved over time. For an isolated system, this law means that energy can change its location within the system, and that it can change form within the system, for instance chemical energy can become kinetic energy, but that energy can be neither created nor destroyed.

From: http://en.wikipedia.org/wiki/Conservation_of_energy