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Rigid body
Beginner
An idealised body whose parts keep fixed distances.
A rigid body is an idealised object whose parts never change their mutual distances. It lets us treat rotation and translation separately. Real objects are close to rigid for small forces.
A steel wheel is almost rigid; a jelly isn't.
Rigid bodies cannot vibrate or deform.
In more detail
A rigid body is an idealised object whose shape and size do not change, so the distance between any two of its points stays fixed. This lets us describe its whole motion with a few quantities.
Real-world uses
- Engineers model bridges and car chassis as rigid bodies when deformation is small.
- Animators use rigid body physics to simulate falling and spinning objects.
- A spinning CD or a car wheel is modelled as a rigid body, so engineers can ignore small deformations when studying its rotation.
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Frequently asked questions
Are real objects rigid?
Only approximately. Real objects deform, but the rigid body model works well when deformation is negligible.
Can a rigid body be non-uniform?
Yes. A rigid body can have any mass distribution as long as its shape stays fixed.
Is a real object ever perfectly rigid?
No. All materials deform a little, but the rigid-body model is accurate enough for most machines and vehicles.