Work and Energy in Physics

Study Notes

The equation for work (W) when force (F) and displacement (d) are constant and aligned is given by W = F × d × cos(θ), where θ is the angle between the force and the displacement direction. If F and d are in the same direction, θ = 0° and cos(θ) = 1. Thus, W = F × d.
A force does negative work when it acts in the opposite direction to the displacement of an object. This often occurs when a force opposes the motion, such as friction resisting an object's movement.

When a ball is thrown upwards, the work done by gravitational force is negative, as gravity acts downward while the ball moves upward, reducing the ball's kinetic energy until it reaches its peak.
Work is a scalar quantity, indicating that it has magnitude but no direction, unlike vector quantities such as force or velocity.

The SI unit of work is the joule (J). One joule is defined as the work done when a force of one newton displaces an object by one meter in the direction of the force.
The unit of measurement for energy in the International System of Units (SI) is also the joule (J), establishing a direct correlation between work and energy.

According to the law of conservation of energy, energy can neither be created nor destroyed; it can only be transformed from one form to another or transferred between objects.
Chemical energy is the type of energy associated with chemical reactions, stored in the bonds of chemical compounds.

Mass–energy equivalence, illustrated by the equation E=mc², implies that an object's total energy is directly proportional to its mass. Therefore, energy contributes to an object's overall mass.
Human civilization requires energy to function, obtained from resources such as fossil fuels, which release energy through combustion, and renewable energy sources like solar, wind, and hydroelectric power.