A Collision to add Energy. So let's analyze a collision which adds the energy. So the 2kg mass which provided the energy had an original momentum of 8.5 units, and a final momentum of -3.5 units, for a total exchange of 12 units. The amplification of momentum is indicated by the apparent result of 12 momentum units being directly exchanged, while 20 momentum units were acquired by the two masses on the lever. Another example of energy not being conserved is gravity.
Gravity creates and destroys energy by creating a force when a mass enters a field.
Physicists say that when an object is lifted against gravity, it acquires a potential energy in proportion to the force times the height. Since the force is the same at both levels, the potential energy must be in the height only. But distance without force cannot change the motion of a mass. The potential energy is not in the distance but in the gravity. Similarly, physicists indicate that no energy would be required to hold an object off the ground at a fixed height, because the distance does not change.