Question

If I only know the mass of one sample of food with a certain amount of Calories, how can I know how many more Calories a larger sample of the same food has?

Answer 1

Calories per gram (`"Cal/g"`) implies calories per gram associated with those calories.

A change-in-food mass is associated with the `"Cal/g"` units, and just like a change in position in `"m"` can be determined from the velocity in `"m/s"`, you need a change-in-food mass to determine the analogy to velocity, the calories-per-gram.

If you only used the initial mass, you only examine the initial state, not the change from the initial state to the final state.

You need the difference in the initial mass and the final mass, and the change-in-food mass gives you the difference between them.