Key Terms

center of mass

weighted average position of the mass

closed system

system for which the mass is constant and the net external force on the system is zero

elastic

collision that conserves kinetic energy

explosion

single object breaks up into multiple objects; kinetic energy is not conserved in explosions

external force

force applied to an extended object that changes the momentum of the extended object as a whole

impulse

effect of applying a force on a system for a time interval; this time interval is usually small, but does not have to be

impulse-momentum theorem

change of momentum of a system is equal to the impulse applied to the system

inelastic

collision that does not conserve kinetic energy

internal force

force that the simple particles that make up an extended object exert on each other. Internal forces can be attractive or repulsive

Law of Conservation of Momentum

total momentum of a closed system cannot change

linear mass density

$\lambda$, expressed as the number of kilograms of material per meter

momentum

measure of the quantity of motion that an object has; it takes into account both how fast the object is moving, and its mass; specifically, it is the product of mass and velocity; it is a vector quantity

perfectly inelastic

collision after which all objects are motionless, the final kinetic energy is zero, and the loss of kinetic energy is a maximum

rocket equation

derived by the Soviet physicist Konstantin Tsiolkovsky in 1897, it gives us the change of velocity that the rocket obtains from burning a mass of fuel that decreases the total rocket mass from $m_{\text{i}}$ down to m

system

object or collection of objects whose motion is currently under investigation; however, your system is defined at the start of the problem, you must keep that definition for the entire problem