Glossary
Angular Momentum
A measure of the rotational inertia of a rotating object, relevant for objects undergoing circular or spinning motion.
Example:
A figure skater spinning on ice conserves her angular momentum as she changes her rotational speed by adjusting her arm position.
Closed System
A system in which no external forces act upon it, meaning no mass or energy enters or leaves the system.
Example:
For the principle of conservation of momentum to apply, a collision between two objects on a frictionless surface is often approximated as a closed system.
Conservation of Momentum
A fundamental principle stating that in a closed system, the total momentum before an interaction (like a collision or explosion) is equal to the total momentum after the interaction.
Example:
When two bumper cars collide, the conservation of momentum ensures that the total momentum of both cars combined remains the same before and after the crash, assuming no external forces.
Elastic Collisions
Collisions in which both momentum and kinetic energy are conserved, typically characterized by objects bouncing off each other without deformation.
Example:
A perfectly bouncy superball hitting a hard floor and rebounding with the same speed and no energy loss is an ideal example of an elastic collision.
Force vs. Time Graphs
Graphical representations where the area under the curve between two time points represents the impulse applied to an object during that interval.
Example:
By calculating the area under a force vs. time graph for a golf club hitting a ball, you can determine the impulse delivered to the ball.
Impulse
The change in momentum of an object, also defined as the product of the average force acting on an object and the time interval over which the force acts.
Example:
When a tennis racket hits a ball, the brief, strong force applied creates an impulse that sends the ball flying.
Impulse-Momentum Theorem
A principle stating that the impulse applied to an object is equal to the change in its momentum.
Example:
Car airbags work by increasing the time over which a force acts during a collision, thus reducing the average force experienced by the occupant for the same change in momentum, as explained by the Impulse-Momentum Theorem.
Inelastic Collisions
Collisions in which momentum is conserved, but kinetic energy is not conserved, often occurring when objects stick together or deform upon impact.
Example:
When a snowball hits a wall and splatters, it's an inelastic collision because kinetic energy is lost due to the deformation of the snow.
Linear Momentum
Momentum associated with objects moving in a straight line, as opposed to rotational motion.
Example:
A soccer ball rolling across a field exhibits linear momentum in the direction of its travel.
Momentum
A measure of how much 'oomph' an object has in its motion, calculated as the product of an object's mass and its velocity.
Example:
A large truck moving slowly can have more momentum than a small car moving fast due to its greater mass.
Rocket Thrust
The propulsive force generated by a rocket due to the expulsion of mass (fuel) at a high velocity.
Example:
The powerful upward force that lifts a space shuttle off the launchpad is its rocket thrust, created by expelling hot gases downwards.
Total Momentum
The sum of the individual momentums of all objects within a defined system.
Example:
Before a collision, the total momentum of a system consisting of two carts is the sum of each cart's individual momentum.
Vector
A physical quantity that possesses both magnitude (size) and direction.
Example:
When describing the velocity of a rocket, you must state both its speed and its direction of travel, making velocity a vector quantity.