Energy, Motion and Forces: Kinetic, Potential, Buoyancy & Friction

Types of Energy and Their Effects

Energy: the cause of motion and the changes that occur throughout the universe.

Heat energy (thermal): energy related to temperature and thermal processes; often perceived as heat.

Electrical energy: an indispensable form of energy, widely used and extended in modern developed societies.

Chemical energy: stored in substances and able to produce movement, heat, electricity and other effects.

Kinetic energy: the energy that a body possesses due to its velocity.

Gravitational potential energy: the potential energy that bodies have because of their position above a reference point such as the ground.

Elastic potential energy: the potential energy stored in deformed objects (springs, elastic materials) that can return to their original shape.

Motion: Position, Trajectory and Distance

Example: a cell phone moves when you change its position over time.

The trajectory (path) describes the route followed by a mobile object; it can be rectilinear, circular, parabolic or varied.

The position of an object (for example, the phone) is a point that indicates its location measured from an origin at a given moment.

Displacement is the difference between the final and initial positions of a mobile object.

Distance traveled is the length of the path followed along the trajectory.

Velocity and Acceleration

Speed / Velocity indicates how quickly a mobile object changes its position. Velocity includes direction; speed is the magnitude of that change.

Instantaneous velocity is the velocity of the object at a specific instant of time.

Acceleration measures the variation of velocity with time.

Types of Motion

Uniform rectilinear motion: motion in which an object moves along a straight line with constant velocity (the average velocity is constant).

Uniform circular motion: motion in which an object moves along a circular path and the magnitude of its instantaneous velocity (speed) is constant.

Forces, Weight and Friction

Force is an interaction that causes changes in the velocity (motion), direction, or deformation of bodies. Forces are measured in newtons (N).

Forces can cause deformation; often deformation and the applied force are directly proportional within elastic limits.

Weight and Gravity

Weight is the force with which the Earth (or another massive body) attracts an object. It depends on the object's mass and the local gravitational acceleration.

Friction and Pressure

Frictional force is the force that surfaces exert on bodies that slide or tend to slide over them.

Pressure (contact force per unit area) is the force applied on a surface divided by the area over which it acts; this concept is important for fluids and contact interactions.

Equilibrium, Buoyancy and Archimedes

Equilibrium is the state of an object in which the vector sum of the forces acting on it is zero; the object can be at rest or moving at constant velocity.

Archimedes' principle: a fully or partially submerged body in a fluid experiences an upthrust (buoyant force) equal to the weight of the fluid displaced by the body.

Buoyancy (thrust) reduces the apparent weight of submerged objects; if the buoyant force equals or exceeds the object's weight, the object will float.

Work, Thrust and Machine Efficiency

Work: a force performs work on a body when the point of application of the force moves in the direction of the force.

Machine performance (efficiency) is the ratio of useful energy output to energy input; it indicates how effectively a machine converts consumed energy into useful work.