Glossary
Accelerate
To change an object's velocity, either by changing its speed, its direction, or both. Acceleration is directly proportional to the net force acting on an object and inversely proportional to its mass.
Example:
A car pressing the gas pedal will accelerate, increasing its speed down the highway.
Buoyant Force
The upward force exerted by a fluid (liquid or gas) on an object immersed in it. This force opposes the weight of the object.
Example:
A ship floats on water because the buoyant force exerted by the water is equal to the ship's weight.
Conservative Forces
Forces for which the work done on an object moving between two points is independent of the path taken, and zero work is done if the object returns to its starting point.
Example:
Gravity is a conservative force; the work done lifting a ball to a certain height is the same whether you lift it straight up or take a winding path.
Direction
The path along which something is moving or pointing. For vector quantities like force, it specifies the orientation of the vector.
Example:
When a sailboat tacks, it changes its direction relative to the wind to continue moving forward.
Electricity
A form of energy resulting from the existence of charged particles (like electrons or protons), either statically as an accumulation of charge or dynamically as a current.
Example:
The flow of electricity through wires powers our homes, lighting up rooms and running appliances.
Energy
The ability to do work or produce heat. It exists in various forms, such as kinetic, potential, thermal, and chemical energy.
Example:
A roller coaster at the top of a hill has maximum potential energy, which converts to kinetic energy as it descends.
Fluids
Substances that can flow, including liquids and gases. Their behavior is governed by principles like pressure, buoyancy, and fluid dynamics.
Example:
Understanding fluids is crucial for designing airplanes, as lift is generated by the flow of air over the wings.
Force
A push or pull on an object that can cause it to accelerate, change direction, or change shape. Forces are vector quantities, possessing both magnitude and direction.
Example:
When you kick a soccer ball, the force from your foot causes the ball to accelerate across the field.
Free Body Diagrams (FBDs)
A visual representation used to analyze forces acting on an object, showing all forces as vectors originating from the object's center of mass.
Example:
To solve a problem involving a block sliding down an inclined plane, drawing a Free Body Diagram helps visualize the gravitational, normal, and frictional forces.
Gases
A state of matter characterized by particles that are widely dispersed and move randomly, filling their container. Their behavior is often described by gas laws.
Example:
The behavior of gases in a hot air balloon, where heating the air makes it less dense and causes the balloon to rise, is a practical application of gas laws.
Gravitational Force
The attractive force that exists between any two objects with mass. Its strength depends on the masses of the objects and the distance between them.
Example:
The Earth's gravitational force keeps the Moon in orbit around it, preventing it from drifting into space.
Heat
The transfer of thermal energy between systems or objects due to a temperature difference. It flows from a region of higher temperature to a region of lower temperature.
Example:
When you place a cold spoon into hot soup, heat transfers from the soup to the spoon until they reach thermal equilibrium.
Ideal Gas Law
A fundamental equation that describes the relationship between the pressure, volume, temperature, and number of moles of an ideal gas ($PV=nRT$).
Example:
Using the Ideal Gas Law, engineers can predict how the pressure inside a sealed container of gas will change if its temperature is increased.
Impulse
The change in momentum of an object, equal to the net force applied to the object multiplied by the time interval over which the force acts.
Example:
An airbag in a car increases the time over which the force of impact acts, thereby reducing the impulse and minimizing injury.
Internal Energy
The total energy contained within a thermodynamic system, including the kinetic and potential energies of its molecules. It can be changed by heat transfer or work done on/by the system.
Example:
When you compress a gas in a piston, you do work on it, increasing its internal energy and often its temperature.
Magnitude
The size or extent of a physical quantity, independent of its direction. For vectors, it represents the length of the vector.
Example:
The magnitude of the earthquake was 7.0 on the Richter scale, indicating its immense energy release.
Net Force
The vector sum of all individual forces acting on an object. It determines the object's acceleration according to Newton's Second Law.
Example:
If two people push a box with equal force in opposite directions, the net force on the box is zero, and it remains stationary.
Newton's Second Law
A fundamental principle stating that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass ($F_{net} = ma$).
Example:
A rocket launching into space perfectly illustrates Newton's Second Law, as the massive thrust (net force) causes its rapid acceleration.
Newtons (N)
The SI unit of force, defined as the force required to accelerate a mass of one kilogram at a rate of one meter per second squared (1 N = 1 kg·m/s²).
Example:
A small apple weighs approximately 1 Newton on Earth, demonstrating the force of gravity acting on it.
Non-Conservative Forces
Forces for which the work done on an object moving between two points depends on the path taken, and non-zero work is done if the object returns to its starting point.
Example:
Friction is a non-conservative force; pushing a box across a rough floor requires more work than pushing it across a smooth, frictionless surface for the same displacement.
Normal Force
The component of a contact force exerted by a surface on an object that is perpendicular to the surface. It prevents the object from passing through the surface.
Example:
When a book rests on a table, the table exerts an upward normal force on the book, counteracting gravity.
Pressure
The force exerted per unit area. In fluids, it results from the collisions of molecules with container walls or immersed surfaces.
Example:
A sharp knife cuts easily because it applies a large pressure over a very small area, even with a moderate force.
Thermodiffusive forces
Forces that arise in fluids due to temperature gradients, leading to the movement of fluid (convection) as warmer, less dense fluid rises and cooler, denser fluid sinks.
Example:
The circulation of air in a room heated by a radiator is driven by thermodiffusive forces, creating convection currents.
Work
The transfer of energy to or from a system by means of a force acting over a displacement. It is calculated as the force multiplied by the displacement in the direction of the force.
Example:
Lifting a heavy box onto a shelf requires work to be done against gravity, transferring energy to the box's gravitational potential energy.