At the conclusion of this chapter, the student should be able to:
- 1. Define the term center of gravity, and explain the basis for its location in the human body.
- 2. Estimate the location of the center of gravity of individuals in any position.
- 3. State the principles of equilibrium, and explain and demonstrate applications of each.
- 4. Locate the center of gravity of an individual using either the reaction board or the segmental method.
Definition of Center of Gravity
The center of gravity of a body is sometimes described as its balance point or that point about which a body would balance without a tendency to rotate. For this reason, the center of gravity is often identified as the point where all the weight of the body or object is concentrated. More accurately, it is the point where the weight of the body may be said to act.
The ability to locate the center of gravity of a body is based on the knowledge of what it takes for a system to be balanced, or in equilibrium. Two conditions must be met:
- 1. All the linear forces acting on the body must be balanced.
- 2. All the rotary forces (torques) must be balanced.
Another way of expressing these necessary conditions for equilibrium is to say that the sum of all the forces acting on the body must equal zero. If there is a downward-directed linear force, there must be an equal upward force so that the vector sum of these forces equals zero. If there is a negative clockwise torque, it must be canceled out by a positive counterclockwise torque of equal magnitude (Figure 14.1).
Figure 14.1
The center of gravity of a body is the point where all forces acting on the body equal zero. In this illustration it is represented as the intersection of the x, y, and z axes. It may be located by application of the principle of torques.
A simple experiment to locate the center of gravity, or balance point, consists of suspending an irregularly shaped object by a string and letting it hang until it ceases to move (Figure 14.2). A vertical line is drawn on the object from the point of suspension in a line that is a continuation of the string. The object is then suspended from another point, and the vertical string continuation line is drawn again. This procedure is repeated one more time. The point at which the three drawn lines intersect is the center of gravity. If the object is suspended from this point, it will hang in whatever position it is placed because the weight of the object is equally distributed about this point and no unbalanced forces (torques) exist.
FAQs
The center of gravity of a body is sometimes described as its balance point or that point about which a body would balance without a tendency to rotate. For this reason, the center of gravity is often identified as the point where all the weight of the body or object is concentrated.
When an object's center of gravity is neither raised nor lower when disturbed? ›
Objects that remain in their new position after being slightly displaced are in neutral equilibrium. Its center of gravity is neither raised nor lowered, and its displacement remains independent from its initial position.
What is the relationship between stability and centre of gravity? ›
Stability is the ability of an object to maintain its balance after being disturbed. The stability of an object is extremely dependent upon its center of gravity. The center of gravity of an object is the point at which we can consider the weight of an object to be concentrated.
What will happen when the center of gravity is brought over the base of support? ›
Balance is attained when the centre of gravity is over the base of support. There are two types of balance: 1. static balance – involves maintaining a desired shape in a stationary position (e.g. handstand in gymnastics); and 2. dynamic balance – involves the control of the body as it moves in space.
Why does the body balance at its center of gravity? ›
The center of gravity occurs in the body at a point where weight is equally distributed on all sides. Center of gravity can also be referred to as center of mass. From this point, a body can pivot in any direction and remain balanced. When standing evenly over your center of gravity, you are in a state of equilibrium.
What is the center of gravity and center of rotation? ›
An object's center of rotation is the point about which it is being rotated. An object's center of gravity is the point around which an object's weight is evenly distributed. These may be the same point (in the case of a hula hoop, or some other object with evenly-distributed weight).
What happens if the center of gravity falls outside the shape What does that mean will the object fall over? ›
An object will topple over once its centre of gravity falls outside its base of support. To answer a brainteaser on whether or not an object will topple over, students can draw a plumb line between the object's centre of gravity and its base.
When an object is stable when its centre of gravity lies above its base? ›
A structure is stable if its centre of gravity lies above its base. An object is unstable when its centre of gravity lies outside its base. In other words, an object is unstable if a line drawn between its centre of gravity and the centre of the Earth does not pass through its base.
Does a low center of gravity lead to more stability True or false? ›
A body is more stable if its centre of gravity is closer to the base than when it is further away.
What makes more objects more stable than other objects? ›
Stable objects have both a broad base of support and a low centre of gravity. The centre of gravity of an object could also be called its balance point. If you support the centre of gravity, the object will balance and be stable.
Ans. In order to measure the stability of an object, two factors need to be determined that are the width of the object's base and the height of the object's centre of mass. The position of the centre helps one to know whether the object will remain standing or tip over.
Which is more stable high or low center of gravity? ›
Structures with a low center of gravity compared to the size of the support area are more stable.
What is the relationship between base of support and stability? ›
In the standing position, the BOS is the area within the feet. So, the postural stability is more increased when the BOS is widened by feet. In other words, the difference of base area changes the postural stability and changes the strategy of postural adjustment.
What is the relationship between the center of gravity and the support base for an object that is in stable equilibrium? ›
Answer and Explanation:
The reaction offered by the support base is equal to the weight acting at the center of gravity. This is how the object on the support base, maintains a stable equilibrium. This is the relationship between the centre of gravity and the support base for an object in a stable equilibrium.
What is the point at which your body is balanced called? ›
Okay, so what is the “center of gravity?” Simply put, it's the point around which the body's mass is equally balanced. You might call this an equal distribution of your weight around an imaginary point at which the effect of gravity and other forces, like inertia, on our mass is either stable or unstable.
What is the point at which our bodies are balanced called? ›
Your center of gravity is the balance point in your body. It's the point at which your upper and lower body weight is balanced. Typically, this is just below the belly button and half way between the lower back and belly when a woman is standing upright. For a man, it is slightly above the belly button.
What is the point about which a body rotates called? ›
Rotation turns an object about a fixed point which is known as the centre of rotation.
What is the tendency of a force to rotate a body called? ›
torque, in physics, the tendency of a force to rotate the body to which it is applied.
