Momentum is a measure of an object's motion, and is calculated by multiplying its mass by its velocity.
Momentum is conserved in a system when the total momentum before an interaction is equal to the total momentum after the interaction. This is known as the law of conservation of momentum.
The momentum of an object can change in two ways: through changes in its mass or its velocity. An increase in either of these factors will result in an increase in momentum, while a decrease in either will result in a decrease in momentum.
According to Newton's third law of motion, for every action there is an equal and opposite reaction. This means that the momentum of Ball 1 will affect the momentum of Ball 2 and the Triangle, as they are all part of the same system. If Ball 1 gains momentum, Ball 2 and the Triangle will experience an equal and opposite change in momentum.
The momentum of a system can be affected by factors such as the mass and velocity of the objects, as well as any external forces acting on the system. In the case of the 3 balls, the momentum can also be affected by the angle and speed at which Ball 1 collides with the Triangle.