Chapter 10: Center of Gravity
In this chapter, we learned about center of gravity and learned how this concept can be applied to balancing and stability.


10.1-Center of Gravity

  • For an object with definite size and shape, the single point that represents that object is known as the center of gravity
  • The center of gravity of an object is the point located at the object's average position of weight
  • The center of gravity for a symmetrical object such as a baseball would be in the geometric center of the object
  • For an irregularly shaped object, such as a baseball bat, the center of gravity would be towards the heavier end because of the uneven distribution of weight among the bat
  • Objects not mad of the same material throughout may have the center of gravity far from the geometric center Ex: hollow ball that is half filled with lead. The center of gravity would be in the lead part instead of the geometric center.
  • mmw_baseball_040108_article.jpg
BASEBALLBAT.jpg
Because of the shape, the bat's center of gravity is towards the heavier end

10.2-Center of Mass

  • Center of gravity can also be considered the center of mass, which is known as the average position of all the particles of mass that make up an object.
  • These terms are interchangeable for most objects on earth
  • There can be a small difference between center of gravity and center of mass when an object is large enough for gravity to vary from one part to another Ex: World Trade Center
10.3-Locating the center of gravity

  • To find the center of gravity in:
    • Uniformed object - geometric center
    • Complex objects - suspend the object from different points, while tracing a line straight down frrom the suspension point, and finally repeat steps and see where the lines intersect
  • An object does not need matter to exist in that place to have a center of gravity
    • Ex. A Donut - In this case the donuts center of mass is the whole in the middle of the donut that contains no matter

http://www.concurringopinions.com/archives/donut.jpg
http://www.concurringopinions.com/archives/donut.jpg


10.4-Toppling

  • Every object contacts a surface in one or more points
  • As long as the center of gravity of an object remains above or hanging below the support base, the object will remain in place
  • However, if the center of gravity moves out and away from the object's support base, it will topple over
  • The rule for toppling: If the CG of an object is above the area of support, the object will remain upright. If the CG extends outside the area of support, the object will topple.
leaning_tower_of_pisa.jpg Why does the Tower of Piza not topple? Because its still over its support base.
  • A vertical line below the Center of gravity falls inside the base
10.5

  • Objects with no net force can be either be easy or hard to tip
    • This all depends on the size of the support base and where the objects center of gravity is located
  • Types of Stability:
    • Unstable Equilibrium- When an object is placed on the edge of the support base and a small push will topple the object
      image002.gif
      http://www.diracdelta.co.uk/science/source/e/q/equilibrium/image002.gif


    • Neutral Equilibrium- When you displace the object and its center of gravity becomes where it stops
      image001.gif
      http://www.diracdelta.co.uk/science/source/e/q/equilibrium/image001.gif


    • Stable Equilibrium- When an object is pushed slightly but it returns to its original position

10.6

  • Your center of gravity is normally 2 to 3 cm below your navel and midway between your front and back
  • Center of gravity is lower in women than men because women are larger in the pelvis and smaller in the shoulders
  • Why can you bend over and touch your toes but bend over against a wall and not be able to touch your toes? This is because you are unable to adjust your body and your center of gravity is outside of where your feet lie.