Glossary
Center of Mass (COM)
The unique point where the system's mass is evenly distributed, acting as the average position of all the mass in the system. It's the point where an object can be balanced.
Example:
For a perfectly uniform baseball bat, the center of mass is near its thick end, which is why it feels heavier there when you try to balance it.
Collision
A collision occurs when two or more objects interact, exerting forces on each other for a short period.
Example:
When a baseball bat hits a fastball, it's a brief, forceful collision between the bat and the ball.
Completely Inelastic Collisions
A special type of inelastic collision where the colliding objects stick together and move as a single combined mass after the collision.
Example:
When a bullet embeds itself into a block of wood and the two move together, it's a completely inelastic collision.
Elastic Collisions
A type of collision where objects bounce off each other, and both momentum and kinetic energy are conserved.
Example:
When two perfectly bouncy superballs collide and rebound without any energy loss, it's an ideal elastic collision.
Inelastic Collisions
A type of collision where objects either stick together or deform, and kinetic energy is not conserved (some energy is lost). Momentum is still conserved.
Example:
A car crash where the vehicles crumple and deform is a classic example of an inelastic collision, as kinetic energy is converted into heat and sound.
Kinetic Energy
The energy an object possesses due to its motion, calculated as half the product of its mass and the square of its velocity.
Example:
A roller coaster at the bottom of a hill has maximum kinetic energy due to its high speed.
Momentum
A measure of an object's mass in motion, calculated as the product of its mass and velocity. It is a vector quantity.
Example:
A heavy truck moving slowly can have more momentum than a light car moving fast, making it harder to stop.
Momentum Conservation
The principle stating that if the net external force on a system is zero, the total momentum of the system remains constant before and after an interaction.
Example:
In a game of billiards, when the cue ball strikes another ball, the total momentum conservation of the system ensures the balls' combined momentum remains the same, just redistributed.
Net External Force
The vector sum of all forces acting on a system from outside the system. It determines the acceleration of the system's center of mass.
Example:
If a rocket in deep space experiences no net external force, its center of mass will continue moving at a constant velocity.
Velocity
The rate at which an object changes its position, including both its speed and direction. It is a vector quantity.
Example:
When solving collision problems, it's crucial to consider the positive or negative direction of an object's velocity to correctly calculate momentum.