## Explanation

### Answer

A screw decreases the **force** needed to do work because it increases the distance through which you apply the force.

### Explanation

The principle behind this effect is closely related to the concept of mechanical advantage. By threading the screw, you effectively transform a small rotational force applied over a longer distance along the threads into a larger linear force over a shorter distance. This mechanical relationship can be described mathematically as:

$\text{Work} = \text{Force} \times \text{Distance}$When utilizing a screw, the **distance** part of the equation is increased significantly due to the helical structure of the threads. This allows a smaller input **force** to produce the same amount of work as a larger force over a shorter distance.

In terms of mechanical advantage, the screw can be visualized as a type of inclined plane wrapped around a cylinder. When using screws, the mechanical advantage can be quantified by:

$\text{Mechanical Advantage} = \frac{2 \pi r}{\text{Pitch}}$Where:

- $r$ is the radius of the screw,
- $\text{Pitch}$ is the distance between threads.

By increasing the distance via the pitch of the threads, you effectively **decrease the input force needed**:

Thus, a screw makes it easier to exert a large output force with a smaller input force, utilizing the increased distance of the thread to your advantage. This property makes screws indispensable in various applications like fastening objects, lifting heavy loads, and adjusting mechanical components.