energy, work & power

1.7.1 | energy

types of energy stores

• kinetic energy - energy of moving objects
• gravitational potential energy - energy due to height in a gravitational field
• chemical energy - energy stored in chemical bonds
• elastic (strain) energy - energy stored in deformed elastic materials
• nuclear energy - energy stored in atomic nuclei
• electrostatic energy - energy due to electric charges
• internal (thermal) energy - energy due to the motion of particles within a substance

energy transfer between stores

energy transfers during events and processes through multiple methods:

• mechanical work - energy transfer through forces causing movement
• heating - energy transfer due to temperature difference
• radiation - energy transfer through electromagnetic waves (e.g., light, sound)

conservation of energy

energy cannot be created or destroyed, only transferred between stores. total energy in a closed system remains constant. in simple examples, kinetic and potential energy convert between each other.

sankey diagrams

sankey diagrams visually represent energy transfers and losses in a system. the width of arrows is proportional to the amount of energy transferred or lost.

1.7.2 | work

mechanical and electrical work

work is done when a force causes displacement in the direction of that force. the energy transferred equals the work done. mechanical work is done by forces moving objects. electrical work is done by currents in circuits.

calculating work

w = fd, where f is the force in the direction of motion and d is the displacement. only the component of force parallel to motion does work. work can also be expressed as w = ∆e, the change in energy of the object.

1.7.3 | energy resources

fossil fuels

chemical energy stored in coal, oil, and natural gas. burned to release energy for electricity generation. non-renewable; finite supply.

biofuels

chemical energy stored in organic matter like plants and animal waste. converted into usable fuels for electricity generation. renewable but requires large amounts of land and water.

geothermal resources

thermal energy from the Earth's core. used to generate electricity by heating water to produce steam. renewable but limited to specific locations.

nuclear fuels

uranium and thorium undergo fission to release energy. generates electricity without greenhouse gases. non-renewable but very dense energy source.

solar energy

solar cells convert light from the Sun directly into electrical power. solar panels use infrared radiation from the Sun to heat water. renewable.

wind energy

wind is driven by solar heating of the atmosphere. turbines convert wind energy into electricity. renewable.

water resources

waves and tides store energy from the Sun and Moon. hydroelectric dams use water behind barriers to generate electricity. renewable and reliable.

advantages and disadvantages

each method differs in renewability (renewable vs non-renewable), availability (constant vs intermittent), reliability, scale, and environmental impact. fossil fuels are reliable but cause pollution. renewables are cleaner but may be less reliable.

1.7.4 | power

definition

power is the rate at which work is done or energy is transferred. it measures how quickly energy is being used or converted. a more powerful device transfers more energy in the same time than a less powerful device.

calculating power

p = w/t, where w is work done and t is time. alternatively, p = ∆e/t, where ∆e is change in energy. power is measured in watts (w) or joules per second (j/s).