Glossary
Center of Mass (COM)
The point representing the average position of a system's mass, where all the mass can be considered concentrated for analyzing motion.
Example:
When a diver performs a somersault, their center of mass follows a smooth parabolic path, even as their body rotates around it.
Closed System
A system where no mass or energy is exchanged with the surroundings, and no net external forces act on it, allowing for the application of conservation laws.
Example:
To analyze the collision of two billiard balls using conservation of momentum, the two balls together can be considered a closed system if friction is negligible.
Conservation of Linear Momentum
A fundamental principle stating that the total linear momentum of a closed system remains constant if no net external forces act on it.
Example:
When a cannon fires a projectile, the conservation of linear momentum explains why the cannon recoils backward as the projectile shoots forward.
Elastic Collisions
Collisions in which both linear momentum and kinetic energy are conserved.
Example:
The collision between two perfectly bouncy superballs is an approximation of an elastic collision, where kinetic energy is nearly conserved.
Impulse (J)
The change in momentum of an object, equal to the average net force acting on the object multiplied by the time interval over which the force acts.
Example:
A tennis racket hitting a ball delivers a significant impulse, causing a rapid change in the ball's velocity.
Impulse-Momentum Theorem
States that the impulse applied to an object is equal to the change in its momentum.
Example:
When a soccer player kicks a ball, the force of the kick over a short duration applies an impulse-momentum theorem, changing the ball's speed and direction.
Inelastic Collisions
Collisions in which linear momentum is conserved, but kinetic energy is not, typically due to energy conversion into heat, sound, or deformation.
Example:
A car crash is a prime example of an inelastic collision, as kinetic energy is lost to the deformation of the vehicles and the sound of the impact.
Momentum (p)
A vector quantity defined as the product of an object's mass and its velocity, representing the 'quantity of motion' an object possesses.
Example:
A heavy truck moving slowly can have the same momentum as a light car moving quickly.
Perfectly Inelastic Collisions
A special type of inelastic collision where the colliding objects stick together and move as a single unit after the collision.
Example:
When a snowball hits a target and sticks to it, they move together as one, demonstrating a perfectly inelastic collision.