Introduction:
A wheel is a circular object that is used in various machines and devices to enable smooth movement. However, a wheel alone cannot function as a machine without an axle. The axle is a central rod or shaft that connects the wheel to a frame or structure. In this response, we will explore the reasons why a wheel cannot be used as a machine without an axle.

1. Definition of a wheel and an axle:
- A wheel is a circular object with a hole in the center, designed to rotate on an axle.
- An axle is a rod or shaft on which a wheel rotates.

2. Purpose of an axle:
- An axle provides stability and support to the wheel.
- It allows the wheel to rotate smoothly and evenly.
- The axle also helps in distributing the weight and load of the machine.

3. Importance of an axle:
- The axle acts as a pivot point for the wheel, allowing it to rotate freely.
- It provides a fixed axis of rotation for the wheel.
- Without an axle, the wheel would not have a stable and controlled rotation.

4. Function of an axle in a machine:
- In machines such as cars, bicycles, or pulley systems, the axle connects the wheel to the chassis or frame.
- The axle allows the transfer of power and motion from the engine or source to the wheel.
- It enables the wheel to rotate with minimal friction and resistance.

5. Limitations of using a wheel without an axle:
- Without an axle, a wheel would have no means of support or stability.
- It would not be able to rotate smoothly and evenly.
- The wheel would also lack a fixed axis of rotation, making it difficult to control its movement.

Conclusion:
In conclusion, a wheel cannot function as a machine without an axle. The axle provides stability, support, and a fixed axis of rotation to the wheel. Without an axle, the wheel would lack stability, controlled rotation, and the ability to transfer power and motion. Therefore, the combination of a wheel and an axle is essential for the operation of various machines and devices.