Movement from A to B
The amount of energy in the body as it moves from A to B. Momentum is created by external forces and remains in the body until removed by an external force.
Eg, we push off the bed for straight bouncing, the moment our feet leave contact with the bed the energy is in our bodies as we continue to propel in to the air, gravity slows us down and returns us back down towards the trampoline. When our feet hit the bed, it quickly consumes the energy from our bodies as the bed dips towards the floor.
In trampolining, we hope that the pupils linear movement will be in an up and down motion on the cross with no travel.
To create linear movement in one spot the vertical force of the trampoline bed must be directed through the centre of the centre of Mass. If the vertical force is off just a little the feet will land away from the point where they started.