1. Angular Momentum 角动量

2. Three fundamental principles
Momentum principle
Energy principle ?

3. Think about the Earth orbiting the Sun.
What is conserved during the orbit?

4. Think about the Earth orbiting the Sun.
What is conserved during the orbit?
Answer:
The translational angular momentum with respect to the Sun.

5. What is the direction of the vector ?
The direction depends on the direction of rotation.
It is perpendicular (垂直) to both and .

6. Angular momentum from the vector cross product
Translational angular momentum around a point A:
Magnitude:
Direction:

7. Example: Find the angular momentum of the particle around points A, B and C.

8. What is the direction of the vector <0,4,0> x <0,0,3> ?

9. What is the direction of the vector <0,0,3> x <0,4,0> ?

11. Even an object moving in a straight line can have angular momentum about some point.

12. 行星

13. 彗星