The Role of Units Physicists, like other scientists, make observations and ask basic questions. For example: how big is an object? How much mass does it have? How far did it travel? To answer these questions, they make measurements with various instruments (e.g., meter stick, balance, stopwatch, etc.). The measurements of physical quantities are expressed in terms of units, which are standardized values. For example, the length of a race, which is a physical quantity, can be expressed in meters (for sprinters) or kilometers (for distance runners.) Without standardized units, it would be extremely difficult for scientists to express and compare measured values in a meaningful way. Distances given in unknown units are maddeningly useless. All physical quantities in the SI system of units are expressed in terms of combinations of seven fundamental physical units, which are units for: length, mass, time, electric current, temperature, amount of a substance, and luminous intensit...
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