Energy is defined as the ability to do work. In physics, work is done when a force causes an object to move over a distance. Therefore, W = ΔE, meaning work is equal to the change in energy. When work is done on an object, energy is transferred to that object, increasing its energy. In the absence of any outside forces, such as friction or air resistance, the total work input is equal to the total work output (energy output). This is a direct application of the law of conservation of energy.
Work can be calculated using the formula:
Where F is the applied force, d is the displacement, and θ is the angle between the force and direction of motion. If the force is applied in the same direction as motion, then θ = 0 and cosθ = 1, simplifying the formula to W = Fd.
Kinetic energy is the energy associated with the motion of an object. Kinetic energy depends on both the mass of the object and its velocity. It is calculated as:
As shown in the formula, an object with a mass and a speed will have a certain amount of kinetic energy. An object with twice the mass and the same speed will have twice the kinetic energy. An object with the same mass but twice the speed will have four times as much kinetic energy, showing that velocity has a greater effect on kinetic energy than mass.
Gravitational potential energy is the energy stored in an object due to its height above the ground. It is calculated as:
Where m is mass, g is the acceleration due to gravity (9.8 m/s2), and h is height. The higher an object is lifted, the more gravitational potential energy it gains.
Mechanical energy is defined as the total energy due to the motion and position of an object. Mechanical energy can be calculated as:
In an ideal system with no friction, mechanical energy remains constant. This is known as the conservation of mechanical energy.
A system is a set of interconnected parts being studied, while everything outside the system is considered the environment.
An open system is one that exchanges both matter and energy with its surroundings (such as a plant or a human body).
A closed system is one that exchanges energy but not matter with its surroundings (such as the Earth).
An isolated system is one that cannot exchange matter or energy with the environment (such as the Universe).
The first law of thermodynamics states that energy cannot be created or destroyed. It can only be transformed from one form to another, and the total amount of energy in a closed system remains constant.
The second law of thermodynamics states that energy transformations are not 100% efficient and that thermal energy always flows naturally from a hot object to a cold object. This leads to an increase in entropy (disorder) in the universe.
Power is the rate at which work is done or energy is transferred. It is calculated as:
Where P is power (watts), W is work (joules), and t is time (seconds). A more powerful machine can do the same amount of work in less time.
Machines make work easier by converting an initial energy input into useful energy output. However, not all input energy becomes useful output; some is lost as waste energy, usually in the form of heat due to friction.
Efficiency (of a machine) is a measurement of how effectively a machine converts energy input into useful energy output. It is calculated as:
Efficiency = (Useful work output) / (Total work input).
Percent efficiency = Efficiency * 100.
No machine is 100% efficient due to energy losses, mainly from friction and heat.
Renewable energy sources are naturally replenished and can be used continuously (such as solar, wind, hydro, geothermal, tidal, and biomass).
Non-renewable energy sources are finite and will eventually be depleted (such as fossil fuels and nuclear fuels).
The extraction and use of energy resources, especially fossil fuels, can have significant environmental impacts:
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