Term
Compare the center of gravity of an object to its center of mass. Do these occur at the same location in the object? 

Definition
yes, as long as g is constant over the mass distribution. The center of gravity of an object is the point at which the entire weight may be considered to be concentrated. If g is constant over the entire mass distribution then the center of gravity coincides with the center of mass. 


Term
A system consists of two masses m_{1} and m_{2} at positions X_{1} and X_{2}. What is the X_{cm}, the position of the center of mass of the system? 

Definition
The center of mass is at x_{cm} = (m_{1}x_{1} + m_{2}x_{2})/m_{1}m_{2} 


Term
A system consists of N particles, with masses m_{1}, m_{2}, ....., m_{n} and positions r_{1}, r_{2}, ....., r_{n}. What is rcm, the position of the center of mass of the system? 

Definition
The center of mass is at r_{cm} = Σ (m_{i}r_{i})/Σ m_{i}
summed over i ranging from 1 to N. 


Term
T or F. The center of mass of a system of particles moves as if all the mass of the system were concentrated there and all the external forces were acting on that point. 

Definition
True. This is Newton's second law as it applies to a system of particles. 

