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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
collision that conserves kinetic energy
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
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
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
λλ, expressed as the number of kilograms of material per meter
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 mimi down to m
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
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