Conservation of Momentum and Energy

What is a Closed System of bodies?

One where no resultant external force is acting.

What is the Principle of Conservation of Momentum?

When bodies in a system interact, the total momentum of the system remains constant, provided no net external force acts on it.

What is an External Force?

A force acting on the system from the outside.

When does the Principle of Conservation of Momentum hold?

Always holds if no net external force acts in the direction in which momentum is considered.

Is Kinetic Energy always conserved in interactions where momentum is conserved?

No, some change in kinetic energy usually takes place.

Is Total Energy always conserved in a collision?

Yes, total energy (including kinetic energy, elastic potential energy, sound energy, internal energy) is always conserved.

How are interactions between bodies classified? (Types of Interactions)

Collisions (total KE remains same or decreases) and Super-elastic interactions (total KE increases).

What is a Collision?

Interaction where total kinetic energy either remains the same or decreases after the interaction.

What is a Super-elastic Interaction?

Interaction where total kinetic energy increases after the interaction.

What is a Head-on Collision?

Velocities of the bodies before and after collision are along the line joining their centres of mass.

What is a Glancing Angle Collision?

Collision not directly head-on.

What happens during a collision between two bodies?

They come close, exert large internal forces (action-reaction pair) on each other for a short time interval.

What is the total initial momentum of bodies in a system (prior to collision)?

ΣPinitial = mA uA + mB u_B (vector sum).

What is the total final momentum of bodies in a system (after collision)?

ΣPfinal = mA vA + mB v_B (vector sum).

What is the Problem-Solving Technique for Conservation of Momentum?

Identify the type of collision, then apply ΣPinitial = ΣPfinal.