Which instrument features sliding masses along three beams to measure mass?

• A. Triple beam balance
• B. Micrometer
• C. Ruler
• D. Thermometer

Answer: (A)

Mass measurement with a balance that uses sliding weights on three beams. This design—three separate beams with riders you slide to set the mass—lets you read different place values (hundreds, tens, and ones) and then add them together to get the total mass. You place the object on the pan, slide the riders until the balance pointer is at zero, and read the numbers on the three beams. This method is specific to the triple beam balance, making it the right tool for measuring mass. The other instruments serve different purposes: a micrometer measures very small dimensions, a ruler measures length, and a thermometer measures temperature.