Glossary
Charges (q1, q2)
Fundamental properties of matter that cause it to experience a force when placed in an electromagnetic field; they can be positive or negative.
Example:
In a lightning strike, massive amounts of positive and negative charges build up in clouds and the ground, leading to a powerful discharge.
Coulomb's Law
A fundamental law describing the electrostatic force between two charged objects, stating it is directly proportional to the product of their charges and inversely proportional to the square of the distance between them.
Example:
Using Coulomb's Law, physicists can calculate the immense force holding atomic nuclei together, despite the repulsion between protons.
Coulomb's constant (k)
A proportionality constant in Coulomb's Law, representing the strength of the electrostatic interaction in a vacuum.
Example:
The value of Coulomb's constant is crucial for determining the magnitude of electric forces in various applications, from particle accelerators to microelectronics.
Distance (r)
The separation between the centers of two charged objects, which significantly influences the magnitude of the electrostatic force.
Example:
Even a small change in the distance between two charged spheres can drastically alter the electrostatic force between them due to the inverse square relationship.
Electric Force ($F_e$)
The specific force acting on an object due to the presence of other electric charges or an electric field.
Example:
In a Van de Graaff generator, the hair of a person standing on it stands on end due to the repulsive electric force between the similarly charged strands.
Electric Forces
Fundamental forces that exist between charged objects, either attracting or repelling them based on the nature of their charges.
Example:
When you rub a balloon on your hair, the electric forces between the balloon and your hair cause them to stick together.
Electrostatic force (F)
The attractive or repulsive force between two charged particles, calculated using Coulomb's Law.
Example:
The electrostatic force between a positively charged glass rod and a negatively charged plastic sheet causes them to pull towards each other.
Equilibrium
A state where the net force acting on an object is zero, meaning the object is either at rest or moving at a constant velocity.
Example:
A charged pith ball hanging motionless in an electric field is in equilibrium, as the electric force, gravitational force, and tension balance each other out.
Force (as a vector)
A physical quantity that has both magnitude and direction, representing a push or a pull on an object.
Example:
When analyzing the motion of a rocket, engineers must consider thrust, drag, and gravity as a force (as a vector) to predict its trajectory.
Free-Body Diagrams (FBDs)
Visual representations used to analyze the forces acting on a single object, showing all forces as arrows originating from the object's center.
Example:
To determine if a charged sphere suspended by a string is in equilibrium, drawing a Free-Body Diagram helps visualize the electric, gravitational, and tension forces.
Gravitational Force ($F_g$)
The attractive force exerted by a massive body (like Earth) on an object, always pointing towards the center of the Earth.
Example:
Even a tiny charged dust particle floating in the air is still subject to the downward pull of gravitational force.
Like charges
Charges that have the same sign (both positive or both negative), resulting in a repulsive electrostatic force between them.
Example:
If you try to push two positively charged magnets together, the like charges will cause them to push apart.
Net Force
The vector sum of all individual forces acting on an object, which determines the object's acceleration according to Newton's Second Law.
Example:
If a charged particle is simultaneously pushed by one charge and pulled by another, the net force determines its overall direction and magnitude of acceleration.
Newton's Third Law
States that for every action, there is an equal and opposite reaction; if object A exerts a force on object B, then object B exerts an equal and opposite force on object A.
Example:
When a charged particle repels another, the repulsive force exerted by the first particle on the second is equal in magnitude and opposite in direction to the force exerted by the second particle on the first, illustrating Newton's Third Law.
Opposite charges
Charges that have different signs (one positive and one negative), resulting in an attractive electrostatic force between them.
Example:
The attraction between a proton and an electron is a classic example of opposite charges pulling towards each other.
Point Charges
Idealized charged objects that are assumed to have their charge concentrated at a single point in space, simplifying calculations.
Example:
When calculating the force between two electrons, we often treat them as point charges because their physical size is negligible compared to the distance between them.
Tension (T)
The pulling force transmitted axially by means of a string, cable, chain, or similar one-dimensional continuous object.
Example:
When a charged pendulum bob is deflected by an electric field, the string exerts a tension force that helps maintain equilibrium.