Final answer:
A spin-up refers to an increase in rate of rotation. It occurs when an object or system increases its rate of spin, such as when a figure skater pulls in her arms and legs closer to her body. Another example is the formation of tornadoes, where storm systems rapidly increase their rate of rotation when the radius of rotation narrows.
Step-by-step explanation:
A spin-up refers to (C) An increase in rate of rotation. It occurs when an object or system increases its rate of spin. An example of spin-up is when a figure skater pulls in her arms and legs closer to her body, causing her rate of spin to increase. Another example is the formation of tornadoes, where storm systems with slowly rotating air rapidly increase their rate of rotation when the radius of rotation narrows.