As stated, Newton’s third law of motion suggests that whatever movement we perform, there will be an equal and opposite reaction to that movement. In order for us to jump, we perform a counter-movement by dipping down. As we press our weight down through our feet into the ground, this force we impart to the ground creates a ground-reaction force which propels our body up along with us extending our legs for more drive in the jump. What we have also done is create momentum that gets transferred from the downward direction and then driven back upwards. We can relate this to the second pull and the first two points of how any horizontal movement will make it difficult later on for the lifts. Momentum is the product of mass and velocity. The larger the mass, the more momentum it can have once it’s moving fast. So this means that the momentum of the barbell as it moves up makes it difficult or requires more force to change its direction. Hence it is important that that momentum is directed in that vertical direction so that less work is needed to maintain its direction of movement.