Single Plane?

1. Oct 21, 2007

captainjack2000

1. A mass is hitting the end of a hinged rod. After impact they begin to rotate.
The motion is then confined to a single plane. why? what plane?

3. I am a bit confused by what they mean by a single plane. Are they saying that there are only x,y coordinates? Is this just a condition for the conservation of angular momentum or a reason why linear momentum cannot apply?

2. Oct 21, 2007

Gokul43201

Staff Emeritus
The motion of any point on a hinged object is always confined to a single plane in the lab-frame. This is the plane that is normal to the axis provided by the hinge.

Consider, for example, the motion of the keyhole on a door, as the door rotates.

3. Oct 21, 2007

captainjack2000

I'm sorry but I still don't understand why it has to be considered in the single plane?

4. Oct 21, 2007

captain.joco

The motion of the mass and the rod is a circle. Circle lies in a place, perpendicular to the angular momentum vector of the objects moving round the hinge... I think