A rigid body is an idealized object that does not change its shape or size, no matter how much force you apply to it.

Defining a Rigid Body

In the real world, objects can stretch or squash. In physics, we imagine a rigid body as a collection of many tiny particles held together at fixed distances. If you push or pull a rigid body, the distance between any two of its particles remains exactly the same. A classic example is a metal ball or a wooden block. Even if you spin them fast or throw them, they keep their exact shape.

Understanding Degrees of Freedom

Degrees of freedom refer to the number of independent ways an object can move. Imagine a single point in space. It can move left-right, up-down, or forward-backward. That gives it three degrees of freedom. A rigid body is more complex because it can also rotate.

Types of Motion

A rigid body in three-dimensional space has six degrees of freedom in total. These are divided into two categories:

• Translational Motion: The object moves from one position to another along the X, Y, or Z axes. This accounts for 3 degrees of freedom.
• Rotational Motion: The object spins around its X, Y, or Z axes. This also accounts for 3 degrees of freedom.

When you combine these, you get 6 degrees of freedom (3+3). If you restrict an object—like a door hinge that only allows rotation—you reduce its degrees of freedom. By understanding these movements, scientists can predict exactly how a machine part or a planet will travel through space.