What are the differences between center of gravity and center of mass?
Center of mass is what most people seem to naturally understand. For example, if you have a CD or DVD, the center of mass is the center of the hole even though there is no mass there. Center of mass is important because conservation of momentum works if a person imagines all the mass to be at the center of mass. If you have a big machine with many moving parts, there is no need to know velocities for each part. You only need to know the entire mass and the velocity that the center of mass moves at. Center of gravity is the same as the center of mass when gravity is constant. But, for very tall buildings, gravity is weaker at the top than at the bottom, so the bottom is more significant, so the center of gravity will be below the center of mass. Center of gravity is important because when solving problems of objects under gravity, a person can imagine that the gravity only acts at the center of gravity rather than acting on each particle. Although the weight of the object is due to the
