Question

This is an interesting phenomenon, and a very difficult one to explain. Both torque and angular momentum must be treated as vectors. Torque causes angular momentum to change according to the following equation: delta L rightarrow = rightarrow delta T To use this equation the direction of a torque vector must be defined. Follow the moment arm with the fingers of your right hand. Then turn your fingers to follow the force. As you do this, your thumb will point in the direction of the torque vector. A bicycle wheel will be set up so that it can be suspended from a rope as it spins. What is the direction of the torque vector for the accompanying diagram? Set the bicycle wheel spinning so that when viewed from the left in the diagram, it is spinning counterclockwise. Release the wheel. What happens? Show the direction of the angular momentum vector. At the head of the angular momentum vector, draw a short vector in the correct direction to represent the change in angular momentum, delta L rightarrow, in a short period of time. Delta t. Apply the rule for vector addition and draw a vector to represent the new angular momentum, L rightarrownew, which is the sum of the original angular momentum, L rightarrow , and the change in angular momentum, delta L rightarrow . How does this change in angular momentum explain the continuous precession of the wheel? Repeat the experiment with the wheel spinning clockwise. Draw diagrams similar to those above and explain what you observe.

Answer 1

direction of angular momentum = direction of angular velocity

= direction of cross product of radius vector and velocity vector

therefore when we see from left direction of angular momentum is towards us

direction of torque=direction of cross product of radius vector and force vector

therefore when we see from left direction of angular momentum is towards us