Which principle states that momentum can be transferred but the total momentum of a closed system remains constant?

Which principle states that momentum can be transferred but the total momentum of a closed system remains constant?

• A. Conservation of Momentum
• B. Conservation of Energy
• C. Newton's Second Law
• D. Kinetic Energy

Answer: (A)

Momentum can move from one object to another, but in a closed system with no external forces, the total momentum remains unchanged. This idea is conservation of momentum: the vector sum of all momenta before an interaction equals the vector sum after. You can see it in a collision where two objects push off each other—their individual momenta change, yet the total momentum of the system stays the same. An easy way to grasp it is to think of two ice skaters starting from rest and pushing apart. They fly in opposite directions with momenta that cancel, so the total momentum is zero both before and after the push. This principle applies even when kinetic energy isn’t conserved, such as in inelastic collisions where some energy is turned into heat or deformation; the momentum balance still holds because it depends on mass and velocity, not just energy. If external forces were acting on the system, like friction from a surface, external impulses would change the total momentum, breaking the closed-system condition. This is why momentum conservation is so useful for analyzing interactions where no external forces are at play.

Momentum can move from one object to another, but in a closed system with no external forces, the total momentum remains unchanged. This idea is conservation of momentum: the vector sum of all momenta before an interaction equals the vector sum after. You can see it in a collision where two objects push off each other—their individual momenta change, yet the total momentum of the system stays the same.

An easy way to grasp it is to think of two ice skaters starting from rest and pushing apart. They fly in opposite directions with momenta that cancel, so the total momentum is zero both before and after the push. This principle applies even when kinetic energy isn’t conserved, such as in inelastic collisions where some energy is turned into heat or deformation; the momentum balance still holds because it depends on mass and velocity, not just energy.

If external forces were acting on the system, like friction from a surface, external impulses would change the total momentum, breaking the closed-system condition. This is why momentum conservation is so useful for analyzing interactions where no external forces are at play.