Pierce conducts an experiment in which waves collide in a way that the energy increases, which means that has occurred

It means the waves collides and constructive interference occurred.

Explanation:

If the two waves coming from the opposite direction collide with each other, there are two way of their interference.

Constructive interference: An interference which results in the increase in energy. And it is when crust of a wave comes on the crust of second wave.Destructive interference: An interference which results in decrease in energy of the resulting wave and colliding waves cancel the result of each other.

Hence in experiment there will be constructive interference.

Mass is the amount of matter in an object.  weight is the measurement of the pull of gravity on an object.  say for example, you travel to the moon which has a different gravitational field compared to the gravitational field of earth. (gravitational fields: earth = 1, moon = 0.165)  now when you are on the moon, the pull of gravity on you is different than on the earth. and as weight is the measurement of the pull of gravity on an object, that means yes, your weight can and will change on the moon.  however, on the moon, on earth or even on jupiter, the amount of mass inside of you remains the same. meaning your physical mass remains constant.  in conclusion it is possible for your weight to change as your mass remains constant.