AP Physics C - Unit 4: Impulse and Momentum

center of mass

The average location of all the mass in an object (or group of objects), represented by a point. (Also known as the "mass-weighted average")

center of gravity

The average location of all of the weight of an object (rather than the mass), represented by a point.

linear momentum

An object's resistance to changes in motion, which is measured by an object's mass multiplied by its velocity.

"real" definition of Newton's 2nd Law

The net force on an object is equal to its change of momentum over time.

impulse

The mechanism for changing an object's linear momentum by applying a force over a duration of time.

Law of Conservation of Linear Momentum

If the vector sum of the external forces on a system is equal to zero (sum of Fx = 0 and sum of Fy = 0), then the total linear momentum of the system before and after an interaction remains the same.

total linear momentum

The vector sum of all of the linear momentums (sum of px and sum of py) of all of the objects in the system.

system

A set of objects that we choose and which may interact with each other.

"isolated" system

A system of two or more objects that are free from the influence of "net external forces".

internal forces

Force pairs (N3L) that are generated between two interacting objects in a system. (These do not count as external forces.)

external forces

Forces that originate from outside of the current system such as gravity, big hand, wind, friction from the ground, etc.

inelastic collision

A collision in which momentum is conserved but kinetic energy is not conserved. The final kinetic energy is less than the initial kinetic energy. With these type of collisions, only conservation of momentum is usable.

completely inelastic collision

A type of inelastic collision in which the two objects collide and stick together, becoming one big mass.

elastic collision

A collision in which both momentum and kinetic energy are conserved. The final kinetic energy after the collision is equal to the initial kinetic energy before the collision. With these type of collisions, both conservation of momentum and conservation of mechanical energy are usable.

ballistic pendulum

A device used to measure the initial velocity of an object, such as a bullet, by applying conservation of momentum during one part of the interaction and conservation of energy during another part.