Glossary
Closed System
A closed system is a collection of objects where no matter or external forces exchange with the surroundings, meaning the total momentum within the system remains constant.
Example:
Consider two ice skaters pushing off each other on a frictionless rink; they form a closed system because no significant external forces act on them.
Elastic Collisions
Elastic collisions are interactions where both momentum and kinetic energy are conserved, typically involving objects that bounce off each other without deformation or energy loss.
Example:
A perfect game of pool involves elastic collisions where the billiard balls bounce off each other and the table cushions, conserving both their total momentum and kinetic energy.
Force-Time Graph
A Force-Time Graph plots the applied force against the duration of its application, where the area under the curve represents the impulse delivered to an object.
Example:
Analyzing the Force-Time Graph of a tennis serve allows a coach to determine the impulse imparted to the ball, indicating how effectively the player transferred momentum.
Impulse
Impulse is the change in an object's momentum, resulting from a force acting over a specific time interval.
Example:
When a baseball bat hits a ball, the brief, strong force applied over a short time interval delivers a significant impulse, causing a large change in the ball's momentum.
Impulse-Momentum Theorem
This theorem states that the impulse applied to an object is equal to the change in its momentum.
Example:
If a car's airbags deploy during a crash, they increase the time over which the force acts on the driver, reducing the average force needed to achieve the same change in momentum according to the Impulse-Momentum Theorem.
Inelastic Collisions
Inelastic collisions are interactions where momentum is conserved, but kinetic energy is not, often due to energy conversion into heat, sound, or deformation, and objects may stick together.
Example:
When two cars collide and crumple, it's an inelastic collision because kinetic energy is lost to the deformation of the vehicles and the sound of the impact, even though the total momentum of the system is conserved.
Law of Conservation of Linear Momentum
This fundamental law states that in a closed system, the total linear momentum before an event (like a collision or explosion) is equal to the total linear momentum after the event.
Example:
When a cannon fires a cannonball, the backward recoil of the cannon and the forward motion of the cannonball demonstrate the Law of Conservation of Linear Momentum, as their combined momentum remains zero (if starting from rest).
Momentum
Momentum is a measure of an object's 'oomph' or its resistance to changes in motion, calculated as the product of its mass and velocity.
Example:
A massive truck moving slowly can have the same momentum as a small car moving very fast, making both difficult to stop.
Open System
An open system is a collection of objects that can exchange matter or energy with its surroundings, allowing its total momentum to change due to external forces.
Example:
A rocket launching into space is an open system because it expels exhaust gases, which are matter leaving the system, and external forces like gravity act on it.
Vector Quantity
A vector quantity is a physical quantity that has both magnitude (size) and direction.
Example:
When a soccer player kicks a ball, its velocity is a vector quantity because it has both a speed (e.g., 20 m/s) and a direction (e.g., north).