Chapter 10 : Center of Gravity Page 136 - 146

10.1 Center of Gravity Center of gravity (CG) is the average position of weight. For a symmetrical object like a baseball, this point is at the geometric center of the object. In a baseball bat, it has more weight at one end than the other end, so the CG is toward the heavier end.

Explain why this is a common misconception: The center of gravity is always in the middle of an object. If the wrench were tossed into the air, no matter how it rotated, its CG would follow a smooth parabola.

10.2 : Center of Mass The center of mass is the average position of matter that make up an object. We can interchange the center of gravity and the center of mass for everyday objects.

The center of mass of the solar system can lie outside the massive sun, not at the sun’s geometric center. Why? Because the masses of the planets contribute to the overall mass of the solar system.

Extra Information When the “average position of mass” is considered, one speaks of the center of mass. For most cases, the center of gravity and center of mass are indistinguishable, so CG will be taken to mean both.

10.3 : Locating the Center of Gravity Explain why this is a common misconception: The center of gravity of an object must be where physical mass exists. The textbook will refer to center of gravity as (CG). How can you locate the CG of an object? By suspending the object from some other point and constructing a second vertical line. The CG is where the two lines intersect.

In the center of the hole 5. Can an object have more than one CG? 4. Where is the CG on a donut? In the center of the hole 5. Can an object have more than one CG? A rigid object has one CG. If it is nonrigid, such as a piece of clay or putty, ans is distorted into different shapes, then its CG may change as its shape is changed. Even then, it has one CG for any given shape.

10.4 : Toppling Rule: if the CG of an object's above the area of support, the object will remain upright. If the CG extends outside the area of support, the object will topple. Work input is needed to raise the CG of a system.

Complete the Males Versus Females activity on page 141 in your textbook. Give two reasons why females can generally do this while males cannot.

Females can generally perform this feat while males generally cannot. This happens because the CG in males is generally highly than in females. This tendency is mainly because females tend to be proportionally smaller in the upper body and large in the pelvic region.

10.5 : Stability We say that an object is balanced so that any displacement lowers its center of gravity is in unstable Equilibrium. We say an object is balanced so that any displacement raises its center of gravity is in stable equilibrium. Place a cone on its side and its CG is neither raised or lowered with displacement. An object in this configuration is in neutral equilibrium.

Describe the movement of CG throughout Figure 10.20 on p 144

Describe the movement of CG in Figure 10.21 on page 144.

10.6 : Center of Gravity of People When you stand with your arms hanging at your sides, your CG is within your body. It is typically 2 to 3 cm below your navel, and midway between your front and back. When you raise your hands vertically overhead, your CG rises 5 to 8 cm. Explain why is this a common misconception: the center of gravity of a person is at a fixed place inside the body. The CG of a person is not located in a fixed place, but depends on body orientation.

Chapter 10 Concept Summary The center of gravity(CG) of an object is the point at the center of its weight distribution. When an object is thrown through the air, its CG follows a smooth parabolic path, even if the object spins or wobbles.

3. For everyday objects, the center of gravity is the same as the center of mass. 4. An object will remain upright if its CG is above the area of support. 5. An object is in stable equilibrium when any displacement raises its CG.