Lecture 15 - Gravity and Centre of Gravity Flashcards
What is the Centre of Gravity (CG)?
The point around which the mass and weight of a body are balanced, regardless of the body’s positioning. It can move when body segments move relative to one another and may even be outside the object (e.g., doughnut).
What is the difference between the Centre of Gravity and the Centre of Mass?
Essentially a matter of terminology. Centre of Gravity is influenced by the gravitational pull downwards, while Centre of Mass involves considerations of forces in three dimensions.
Why is locating the CG in humans challenging?
The human body is not rigid but composed of multiple moveable interconnected segments, changing its mass distribution and CG with every change in body configuration.
How does the suspension method locate CG?
By suspending an object at a point and identifying CG along a line directly below; suspending from two points locates CG at their intersection.
What is the balancing method for locating CG?
Involves balancing the body on a board atop a fulcrum, with the CG located directly above the fulcrum in various postures.
Describe the reaction board method for locating CG.
Uses a lever board with one end on a fulcrum and the other on a scale. The location of the body’s CG is determined by solving for ‘d’ to understand the torque developed by the body’s weight and the weight of the board.
What is the segmental method for locating CG?
Uses film or electronic images to estimate CG based on the body’s segments. It requires estimating the location of segment CG from joint locations and segment weight from total body weight using standardized data.
How is understanding CG applicable in biomechanics?
Precise measurement of body and segment locations aids in investigating human movement, including locomotion, motor skill acquisition, ergonomics, and rehabilitation outcomes.
REVIEW THE EQUATIONS IN THE DOCX
Assume a person is standing with her hands at her sides. She then raises her arms so that they are stretched out in front of her.
a) In what direction(s) do you expect her CG moved as she raised her arms, if at all?
b)Would holding a pie in her hands change anything regarding the movement (or lack of movement) in her CG?
a) CG will move up and forward
b) If you include the pie in the system, it will change the CG, however if you don’t include the pie in the system and just look at the person, the CG will not change
