The discussion revolves around the effects of gravity on torque, particularly in relation to a system involving a turntable and its axis of rotation. Participants are exploring the concept of torque as it relates to forces acting in different directions, specifically questioning why gravity does not seem to contribute to torque along the z-axis.
The conversation is ongoing, with participants raising questions about the direction of torque and angular momentum. Some guidance has been offered regarding the relationship between the direction of forces and the resulting torque, but there remains uncertainty about the implications for the specific scenario involving the turntable.
Participants are considering the scenario where a lump of putty is dropped onto a stationary turntable, prompting questions about the resulting torque and whether it would cause the turntable to tip. There is an exploration of assumptions regarding the system's behavior under the influence of gravity.
Why couldn't it ? Torque is defined as the cross product of the distance from the origin and the net force, right ?kuruman said:
Almost. Distance is a scalar, not a vector. If force ##\vec{F}## is applied at position vector ##\vec{r}##, the torque about the origin is ##\vec{r} \times \vec{F}##.Physicslearner1 said:
135 degrees in the xy plane ?kuruman said:
And what is the angle between the vector product and each of the original vectors?Physicslearner1 said:
It's perpendicular to both of themharuspex said:
Right. And the force of gravity is in the z direction, so any torque it exerts must be at right angles to the z direction.Physicslearner1 said:
Ok, but I'm still not sure of understanding why torque is disregarded.haruspex said:
For the moment, suppose the turntable is stationary. We drop a lump of putty on one edge. This exerts a torque about a horizontal axis. Will the turntable tip? Why not?Physicslearner1 said: