What happens to a body when a couple is applied?

When a couple is applied to a body, it creates a torque, which is a rotational force that leads to rotation around a point or axis. This rotational movement occurs without causing any translational movement, meaning the center of mass of the body does not shift in a straight-line path. The application of a couple involves two equal but opposite forces acting at a distance from each other, which contributes to this property.

In this context, we can see that linear motion, remaining stationary, or compressing and expanding are not characteristics of a couple's effect. Instead, the defining outcome is the rotation generated around the center of mass or another defined axis, making rotation without translational movement the correct answer. This principle is essential in understanding how forces interact with objects in orthodontics, as it parallels how orthodontic forces can produce movement or rotation of teeth without necessarily translating them through space.