# Centre-of-mass reference frame

physics

**Learn about this topic** in these articles:

### classical mechanics

- In mechanics: Centre of mass
This is sometimes called the centre-of-mass frame. In this frame, the momentum of the two-body system—i.e., the constant in equation (51)—is equal to zero. Writing each of the

Read More’s as the corresponding**v***d*/**r***dt*, equation (51) may be expressed in the form - In mechanics: Relative motion
This is the centre-of-mass (or centre-of-momentum) frame mentioned earlier. Then, for example, in the collision between two bodies of the same mass discussed above, the two bodies always have equal and opposite velocities, as shown in Figure 14. It should be noted that, in this frame of reference,…

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