The axis of rotation is the single line about which all particles of a body undergoing pure rotational motion revolve.
When a body experiences purely rotational motion, a fundamental concept is the line around which this rotation occurs. This specific line is known as the axis of rotation.
Defining the Axis of Rotation
Based on the provided reference, purely rotational motion is characterized by a specific condition: every particle within the rotating body moves in a circular path around a single, consistent line. This line is precisely what is called the axis of rotation.
The reference states: "Purely rotational motion occurs if every particle in the body moves in a circle about a single line. This line is called the axis of rotation."
This means that if you could track the path of any individual tiny piece or particle of the rotating object, you would find it orbiting this central line.
Key Characteristics
Understanding the axis of rotation involves recognizing a few key characteristics highlighted by the nature of pure rotational motion:
- Circular Paths: Every particle within the body traces a circular path. The center of each circle lies on the axis of rotation.
- Consistent Angular Displacement: The reference notes that "the radius vectors from the axis to all particles undergo the same angular displacement at the same time." This means that as the body rotates, every point on the body effectively turns through the same angle simultaneously relative to the axis.
- Location: The axis of rotation need not go through the body. This is an important point; the axis can be internal (like the Earth's axis passing through its core) or external (like the axis of a merry-go-round, which runs vertically through its center point, but the riders rotate around it).
Practical Examples
To visualize the axis of rotation, consider these common examples:
- A Spinning Top: The axis is a vertical line running through the center of the top, from its point to the top surface.
- The Earth: The axis is an imaginary line passing through the North and South Poles. The entire planet rotates around this internal axis.
- A Door Hinge: The axis of rotation is the line running vertically through the hinge pins. The door rotates around this external line.
- A Ferris Wheel: The axis is the horizontal line passing through the center hub of the wheel.
Axis Location: Internal vs. External
As mentioned, the axis doesn't have to pierce the body itself. This flexibility is key to understanding various types of rotational motion.
| Axis Location | Description | Example |
|---|---|---|
| Internal | The axis passes through the physical body. | Spinning top, Earth's rotation |
| External | The axis is located outside the physical body. | Door hinge, orbiting planet |
In both cases, particles of the body rotate in circles, with the center of these circles lying on the axis. The axis provides the central reference line for the rotational movement.
In summary, the axis of rotation is the defining line that orchestrates the circular motion of every particle within a body undergoing rotation, serving as the anchor point for its angular movement.
