Final answer:
The imaginary vertical line running from the center of gravity to the base of support is fundamental in understanding balance and stability in Physics. Human stability can be enhanced by widening the base of support and lowering the center of gravity, as depicted in various figures illustrating posture adjustments to maintain balance.
Step-by-step explanation:
An imaginary vertical line that extends from the center of gravity to the base of support is a crucial concept in understanding how humans and objects maintain balance. In Physics, the center of gravity (cg) is the point where the entire weight of the body or object is evenly distributed.
Stability is affected largely by the location of this center relative to the base of support. For example, as depicted in Figure 9.16(a) and Figure 9.18(a), an adult's center of gravity is typically above the hip joints and lies between narrowly-separated feet, providing a stable equilibrium laterally.
Adjustments such as spreading the feet further apart or bending the knees, enhance stability by enlarging the base of support and lowering the center of gravity. Objects like a pencil standing on its eraser demonstrate this principle of balance on a smaller scale.
When carrying additional loads, as with a student with a shoulder bag or carrying books, humans instinctively adjust their posture to keep the overall center of gravity over their base of support to prevent falling.