Rotary mass, also known as moment of inertia or rotational inertia, describes how easily or difficult it is to start or stop a rotating object. It depends on both the object's total mass and how that mass is distributed relative to the axis of rotation. A higher rotary mass indicates a greater resistance to changes in rotation.
Understanding Rotary Mass
The concept of rotary mass is crucial in understanding rotational motion. It's analogous to linear mass (or simply mass) in linear motion, where a larger mass resists changes in linear velocity. However, unlike linear mass which only depends on the total mass, rotary mass also considers the distribution of that mass. A mass concentrated further from the axis of rotation contributes more significantly to the rotary mass than the same mass closer to the axis.
Examples
- A solid cylinder has a lower rotary mass than a hollow cylinder of the same mass because the mass in the solid cylinder is distributed closer to the axis of rotation.
- A figure skater pulling their arms closer to their body reduces their rotary mass, allowing them to spin faster. Conversely, extending their arms increases their rotary mass, slowing their spin.
Rotary Mass vs. Rotary (Traffic Circle)
It's important to note that the term "rotary" can also refer to a type of traffic intersection, often called a roundabout in other parts of the United States, particularly in Massachusetts. This is unrelated to the physics concept of rotary mass. The Wikipedia article on "Rotaries in Massachusetts" (https://en.wikipedia.org/wiki/Rotaries_in_Massachusetts) clarifies this distinction.
The provided text emphasizes the physics definition: "The rotational mass of an object is a description of how easy or difficult it is to rotate a body or to stop it once it is rotating." (https://ux1.eiu.edu/~cfadd/3050/Ch08Rot/RotMs.html)
