1. Devil physics The baddest class on campus Pre-DP Physics

2. Lsn 7-8: Center of mass Lsn 7-9: CM for the human body

3. Questions From Reading Activity?

4. Objectives
Explain the differences between translational motion, rotational motion, and general motion.
Know the meaning of the term center of mass.
Explain why knowing the center of mass is important to translational motion.

5. Objectives
Know that the center of mass can be calculated from any reference point.
Calculate the center of mass of various objects in both the x-axis and y-axis.
Calculate the center of mass of various objects using different reference points.

6. Objectives
Know the meaning of the terms center of gravity and geometric center.
Calculate the center of mass of different human body parts and the human body as a whole using representative percentages of mass and height.

7. Introductory Video: Center of Mass and Momentum

8. General Motion
Up until now we have only been dealing with translational motion, linear movement
We also need to think about rotational motion or, a way to get around it

9. General Motion The way we get around it is general motion
We consider the motion of the center of mass

10. General Motion
“The general motion of an extended body (or system of bodies) can be considered as the sum of the translational motion of the center of mass (CM), plus rotational, vibrational, or other types of motion about the CM.”

11. Center of Mass
“. . . one point that moves in the same path that a particle would if subjected to the same net force.
Also said to be the point about which all forces are said to be applied.
Center of mass often corresponds to the geometric center, but only if the density of the material is uniform

12. Center of Mass
Computing center of mass

13. Center of Mass
Computing center of mass
Example Problem

14. Center of Mass of the Human Body

15. Center of Mass of the Human Body
Find the center of mass of a person who is 170cm tall and has a mass of 80kg.
Body Part x
Mass xm
Head
Trunk and neck
Upper arms
Lower arms
Hands
Upper legs
Lower legs
Feet
Total Mass

16. Center of Mass Computing center of mass
Find the center of mass of a straight leg
Height = 170 cm
Mass = 80 kg

17. Center of Mass Computing center of mass
Find the center of mass of a bent leg
Height = 170 cm
Mass = 80 kg
Now we have to find the center in both x- and y-axes

18. Σary Review
Can you explain the differences between translational motion, rotational motion, and general motion?
Do you know the meaning of the term center of mass?
Can you explain why knowing the center of mass is important to translational motion?

19. Σary Review
Do you know that the center of mass can be calculated from any reference point?
Can you calculate the center of mass of various objects in both the x-axis and y- axis?
Can you calculate the center of mass of various objects using different reference points?

20. Σary Review
Do you know the meaning of the terms center of gravity and geometric center?
Can you calculate the center of mass of different human body parts and the human body as a whole using representative percentages of mass and height?

21. Questions?

22. Homework
#46-50, 52-55

23. Foreshadowing Video: Anatomy and Muscles