# I Rotation vs Translation for elbow joint

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1. Jul 19, 2017

### physics gal

If I were to cut the string and let the board move, I know I would get rotation. But, since the center of mass of the beam is moving as well (in a circle) could I also say that the board is translating once the string is cut?

2. Jul 19, 2017

### .Scott

Yes.
Assuming the beam is free to pivot about the hinge at its left end, it would both rotate and translate.

3. Jul 19, 2017

### physics gal

So even though the beam will be tracing a large circle around the hinge (or more likely swinging back and forth) we can call this translation? My reasoning was because the center of mass of the board is moving as it swings. Is that correct?

4. Jul 19, 2017

### sophiecentaur

The Centre of Mass of the board would drop and move to the left so that would be looked upon as translation. To avoid this, you would need to (appropriately) raise the elbow joint and move it to the right. Then you would have only rotation

5. Jul 19, 2017

### physics gal

Even though not all movement vectors of the object are moving in space by the same amount in a given direction, we can still call this translation?

6. Jul 19, 2017

### sophiecentaur

Why not? The translation doesn't need to be in a straight line or in a chosen direction. We are talking in terms of translation of the CM.

7. Jul 20, 2017

### A.T.

Yes, you can decompose the same motion into rotation and translation in different ways.