Work, Energy, and Power

• This covers Work and Energy, Conservation of Energy, Kinetic Energy, Potential Energy, Gravitational Potential Energy, Power, and Efficiency.

Energy

• A relatively recent concept from the 1800s.
• Understanding energy is fundamental for analyzing various processes.
• Energy analysis is more useful than Newton's laws when motion becomes complicated.
• Energy is an abstract concept, not a tangible substance like matter.
• It takes many forms, like stored in food, a moving body, combustion, or electrical energy.
• In any process, energy changes forms, but the total energy is always conserved.

Work

• Has a specific meaning in physics, different from the general idea of effort.
• It involves both Force and displacement.
• When a force acts on a body and moves it a distance in the direction of the force, work is done: W = Fd.
• The unit of work is the joule (J), equivalent to a newton-meter.
• The concept of work applies even when force and displacement are not in the same direction.
• In general, work involves the component of force in the direction of displacement.
• Work can be calculated, using the equation Work = F * cos(θ) * d.

Kinetic Energy

• Kinetic energy measures the work an object can do due to its motion.
• A moving fridge can do work on a man.
• A moving bat can do work on a ball.
• Kinetic energy depends on mass and velocity.
• Increase in kinetic energy of the body is defined, this equals to the work done by the force on the body.
• Starting from rest (vi = 0) and applying a force F over a distance d until the final velocity is v.
• Final result: W = KE = (1/2) * mv^2.

Potential Energy

• Potential Energy is energy stored by an object as a consequence of its position.
• Examples include a ball next to a compressed spring.
• Exists at the microscopic level, arising from the relative position of electric charges.
• Examples: chemical potential energy and nuclear potential energy.

Gravitational Potential Energy

• It takes work to raise an object against Earth's gravity.
• Has the ability to do work, i.e., it has potential energy
• Work is required to raise the ram against the Earth's gravity.
• The ram now has the ability to do work i.e. it has potential energy.
• Potential energy is then converted to kinetic energy, then to work, then to heat.
• To quantify gravitational energy only, we need to ensure kinetic energy doesn't change by raising the object at a constant velocity.
• The work done by the force F to raise the object is W = Fd = Fh = mgh.
• Change in potential energy PE = mgh.

Conservative and Non-Conservative Forces

• Conservative forces result in conservation of mechanical energy, meaning PE + KE remains constant.
• Non-conservative forces are dissipative, like friction.
• The work done by friction causes mechanical energy to seemingly disappear, reappearing as heat energy, but energy is conserved.

Conservation of Total Energy

• Energy occurs in many forms.
• Energy can be changed into different forms, but it is never created or destroyed (Conservation of Energy).
• Total energy is always conserved, even when mechanical energy isn't.

Power

• Power doesn't relate to how much work is done.
• The concept used to describe how fast work is done.
• Power = work done / time taken.
• Power = P = W/t.
• The units of power are watts (W), with 1 watt equal to 1 joule per second (J/s).

Efficiency

• Efficiency = Work output / Work in = Work output / Energy used.
• A certain block and tackle is 40% efficient, and provides 180 J of work, that much of the work is output.