Glossary
Angular acceleration (α)
The rate of change of angular velocity, indicating how quickly an object's rotation speeds up or slows down.
Example:
When a bicycle wheel starts from rest and spins faster, it experiences angular acceleration.
Angular velocity (ω)
The rate at which an object rotates or revolves around an axis, measured in radians per second.
Example:
A spinning record has a constant angular velocity, meaning it completes the same number of rotations per second.
Centrifugal Force
A fictitious or apparent force that seems to push an object away from the center of a circular path, but is not a real force.
Example:
When a car turns sharply, the feeling of being pushed outwards is due to inertia, not a real centrifugal force.
Centripetal Acceleration (a_c)
The acceleration of an object moving in a circular path, always directed towards the center of the circle.
Example:
As a car rounds a curve, its centripetal acceleration is what keeps it from going straight, pulling it towards the center of the turn.
Centripetal Force
The net force that acts on an object moving in a circular path, always directed towards the center of the circle.
Example:
The tension in a string keeping a ball swinging in a circle is the centripetal force.
Change
The alteration of a system's state, such as its motion, speed, or direction, due to interactions.
Example:
A car applying its brakes causes a change in its velocity, slowing it down.
Fields
Regions in space where invisible forces, like gravity, exert influence on objects.
Example:
The Earth creates a gravitational field around it, pulling objects like satellites towards its center.
Force Interactions
Descriptions of how objects exert forces on each other, leading to changes in motion.
Example:
When a soccer player kicks a ball, there's a force interaction between the player's foot and the ball, causing the ball to accelerate.
Frame of Reference
The perspective or coordinate system from which motion and forces are observed and measured.
Example:
When you're sitting on a moving train, your frame of reference might consider the train car as stationary, while an observer on the ground sees you moving.
Free-Body Diagrams (FBDs)
Visual representations that show all the forces acting on a single object, essential for analyzing its motion.
Example:
Drawing a Free-Body Diagram for a block on an inclined plane helps identify the normal force, friction, and gravitational force acting on it.
Gravitational Acceleration (g)
The acceleration experienced by an object due to the gravitational force of a massive body, varying with the mass and radius of the body.
Example:
On Earth's surface, the gravitational acceleration is approximately 9.8 m/s², causing objects to fall downwards.
Gravitational Field
The region of space around a massive object where another object would experience a gravitational force.
Example:
The Moon is within Earth's gravitational field, which is why it orbits our planet.
Gravitational Force
The attractive force between any two objects with mass, proportional to their masses and inversely proportional to the square of the distance between them.
Example:
The gravitational force between you and the Earth keeps your feet firmly on the ground.
Gravitational Mass
A measure of how strongly an object interacts with a gravitational field, determining the gravitational force it experiences.
Example:
The gravitational mass of a planet determines how much it pulls on other celestial bodies.
Inertial Frame of Reference
A non-accelerating frame of reference where Newton's laws of motion hold true without the need for fictitious forces.
Example:
A person standing still on the ground is in an inertial frame of reference, observing objects move according to Newton's laws.
Inertial Mass
A measure of an object's resistance to changes in its state of motion (i.e., its resistance to acceleration).
Example:
A bowling ball has a much greater inertial mass than a tennis ball, making it harder to accelerate.
Newton’s Universal Law of Gravitation
The fundamental law stating that the gravitational force between two masses is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers.
Example:
Using Newton's Universal Law of Gravitation, scientists can calculate the force pulling a spacecraft towards Mars.
Non-Inertial Frame of Reference
An accelerating frame of reference where fictitious forces appear to act on objects to explain their motion.
Example:
Inside a car that is rapidly accelerating, you feel pushed back into your seat, which is a fictitious force experienced in a non-inertial frame of reference.
Rotational Kinematics
The study of rotational motion without considering the forces that cause it, using angular quantities like angular position, velocity, and acceleration.
Example:
Analyzing how a spinning top slows down over time, considering its initial and final angular velocities, falls under rotational kinematics.
Systems
Objects with mass and structure that can be analyzed as a distinct entity in physics.
Example:
When analyzing a roller coaster, the roller coaster car and its passengers can be considered a system.
Uniform Circular Motion
The movement of an object in a circular path at a constant speed.
Example:
A satellite orbiting Earth in a perfectly circular path at a steady speed is undergoing uniform circular motion.
Vector
A physical quantity that has both magnitude (size) and direction.
Example:
Your velocity while running is a vector because it includes both your speed (e.g., 5 m/s) and the direction you're heading (e.g., north).
Vector Field
A region of space where a vector quantity is defined at every point, showing both magnitude and direction.
Example:
A weather map showing wind speeds and directions across a region is an example of a vector field for wind.