Glossary
Air Resistance/Resistive Force
A type of fluid friction that opposes the motion of an object through the air or another fluid.
Example:
A cyclist tucks into an aerodynamic position to minimize air resistance and go faster.
Applied Force
A force exerted directly on an object by a person or another object, often a push or a pull.
Example:
When a student pushes a desk across the classroom, their push is an applied force causing the desk to accelerate.
Buoyant Force
An upward force exerted by a fluid that opposes the weight of an immersed object, causing it to float or appear lighter.
Example:
A submarine uses its ballast tanks to adjust its density, allowing the buoyant force to either lift it or let it sink in the water.
Center of Gravity
The point where the entire weight of an object appears to act, often used as the point of application for the gravitational force in FBDs.
Example:
A tightrope walker adjusts their body to keep their center of gravity directly above the rope for balance.
Coefficient of Kinetic Friction
A dimensionless value that quantifies the ratio of the kinetic frictional force to the normal force when an object is sliding over a surface.
Example:
A low coefficient of kinetic friction for ice explains why a hockey puck slides easily across its surface.
Conservation of Energy
A fundamental principle stating that the total energy of an isolated system remains constant, though it can transform from one form to another.
Example:
In a roller coaster, the principle of Conservation of Energy explains how potential energy at the top of a hill converts into kinetic energy at the bottom.
Electric/Magnetic Forces
Forces arising from the interaction of electric charges (electric force) or moving charges/magnetic fields (magnetic force).
Example:
The attraction between opposite charges, like a balloon sticking to a wall after being rubbed, is due to an electric force.
External Forces
Forces originating from outside the system or object of interest that cause changes in its motion.
Example:
For a book resting on a table, the gravitational force and the normal force from the table are external forces acting on the book.
Free-Body Diagram (FBD)
A visual representation of all external forces acting on a single object, used to analyze its motion or equilibrium.
Example:
When analyzing a car braking, drawing a Free-Body Diagram helps visualize the forces of friction, gravity, and the normal force acting on it.
Friction
A force that opposes relative motion or attempted motion between two surfaces in contact.
Example:
The friction between your shoes and the ground allows you to walk without slipping, converting your forward push into motion.
Gravitational Force
The attractive force between any two objects with mass, commonly experienced as weight pulling an object towards the Earth's center.
Example:
A skydiver experiences a significant gravitational force pulling them downwards, accelerating them towards the Earth.
Ideal Gas Law
A fundamental equation ($PV=nRT$) that describes the relationship between pressure, volume, temperature, and the number of moles of an ideal gas.
Example:
Using the Ideal Gas Law, you can predict how the pressure inside a sealed container of gas will change if its temperature is increased.
Net Force
The vector sum of all individual forces acting on an object, determining its acceleration according to Newton's Second Law.
Example:
If a tug-of-war team pulls with 500 N to the right and the opposing team pulls with 450 N to the left, the net force on the rope is 50 N to the right.
Normal Force
The component of a contact force perpendicular to the surface that an object is resting on or interacting with.
Example:
When you push a box across the floor, the floor exerts an upward normal force on the box, preventing it from falling through.