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Center of Gravity - Jenny Green





Principle(s) Illustrated

  1. Gravity- pulls things to the center of the Earth
  2. Gravity in men vs women and it's location

Physics Standards

                Motion and Forces
  • 1.e. Students know

    the relationship between the universal law of gravitation and the effect of gravity on an object at the surface of Earth.

Questioning Script

Prior knowledge & experience:

Prior knowledge is that traditionally men are stronger with upper body strength as compared to women.

Root question:

Who is stronger? Men or women?

Target response:

Women, when looking at their center of gravity which is located in their hips.  For men, it is located more in their shoulder region

Common Misconceptions: Students think that males are automatically stronger than females, especially upper body strength.  

Materials: 

          1.  A straight backed chair and wall space

          2.  A few male and female students.


Procedure: 

           a.  stand exactly two foot-lengths away from the wall ( by measuring toe to heel off 

                wall with shoes on).

           b.  bend over with a straight back (turning in the hips) and let your head lean against

                the wall.

           c.  Ask someone to hand you the straight-back chair (with back against the wall).

            d.  Lift the chair while your head is still leaning against the wall. 

           e.  with the chair in lifted position, try to straighten up (me cannot do this but a

               woman can!)  

Questions:

        

1. Why can girls or women straighten up and boys or men, not?

2.  Is the weaker sex really stronger? Explain.

3.  What is the difference between how men are built and how women are built?

4.  Where is the center of gravity located in the above pictures?

5.  How do you think shoe size might affect this experiment? (men vs. women's average shoe size)

Explanation: 

    The result of this event has nothing to do with strength.  It lies in the difference of the location of the center of gravity of male and female bodies.  Also important is the difference in foot size.  The center of gravity of the female body is located much lower, in the hips, while the male body is located up much higher, in the shoulders.  The male foot size is also generally much bigger than females, and so he will be forced to actually stand farther away from the wall than the female.  When he bends over, his center of gravity gets shifted beyond his toes, but the females center of gravity stays over her feet, and straightening up is much easier for her.  

       

                                        


MOVIES:

also included in this web site is video analysis and graphing on the x and y axis. 

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