Physics 5054/12 — May/June 2016

Walkthrough

The question asks which instrument gives a reading that is the circumference of a golf ball.

• The circumference is the distance around the curved surface of the sphere.
• A tape measure is flexible, so it can be wrapped around the ball and read directly. This makes it the correct instrument.
• Calipers measure the diameter or another straight-line distance across the ball, not the circumference.
• A micrometer measures very small straight-line distances, such as the thickness or diameter of a small object.
• A rule is rigid, so it cannot be wrapped around the ball to measure the curved circumference directly.

Therefore, the correct option is D.

Key Takeaways

• Circumference is a curved length around an object.
• Flexible instruments, such as a tape measure, are needed to measure curved lengths directly.
• Rigid instruments such as calipers, micrometers and rules measure straight-line distances.

Common Mistakes

• Choosing calipers or micrometer because they are precise, but they measure diameter or thickness, not circumference.
• Thinking a rule can measure a curved length by placing it across the ball; that gives a straight-line distance, not the circumference.

Things to Be Careful About

• Read the wording carefully: the question asks for circumference, not diameter.
• A tape measure is the only listed instrument that can follow the curved surface of the ball.