3 ideas
Physics advances by observing a phenomenon, proposing a testable hypothesis to explain it, and then designing experiments whose results can confirm or overturn that hypothesis. A theory survives only while repeated measurement agrees with it, so any accepted law stays provisionally true and can be revised when new evidence contradicts it.
A small set of fundamental quantities, such as length, mass, time, temperature, electric current, luminous intensity, and amount of substance, is defined independently with its own SI unit. Every other quantity, such as velocity, force, pressure, or energy, is derived by combining these, so its unit and dimensions can be reconstructed from the fundamental ones. Dimensional consistency therefore becomes a quick check on whether an equation can possibly be correct.
Energy can convert between forms, including kinetic, potential, heat, sound, light, chemical, and electrical, but the total in a closed system stays constant. Energy that seems lost, for example to friction, has usually become heat or sound.