# Does two dimensional motion imply conservation of angular momentum?

1. Dec 16, 2013

### anamariann123

Hello!

I have a system composed by a particle attached to four springs that lie on the xy plane. The motion of the particle occurs on the xy plane. I wanted to know if the angular momentum is conserved. Thanks for your help :)

2. Dec 16, 2013

### K^2

Momentum is conserved if there is no external torque. If you have multiple springs going to a point, you probably have some torque on that point.

3. Dec 16, 2013

### HallsofIvy

Staff Emeritus
Perhaps you are thinking "the angular momentum vector is perpendicular to the plane of motion. Since this is two dimensional, there cannot be such a vector." That is mistaken. The fact that motion is "two dimensional" means that the motion occurs in two dimensions. It does not mean there is NO third dimension.

4. Dec 16, 2013

### anamariann123

I know the angular momentum is orthogonal to the plane of motion, but I would like to know if it is constant.

5. Dec 16, 2013

### K^2

Not in general, no. If the springs were attached to other objects that are free to move, it would be, because that would be a closed system. But if springs are attached to fixed points, it's the same as supplying external torque, so angular momentum will not be conserved.