Unit Four Content Page
In this unit, we studied energy. We applied this to energy problems using bar graphs, identified the different types of work, and learned about power and horsepower.
Representing Energy Transfers with Bar Graphs
In order to represent energy transfers in energy problems, we used a specific type of bar graph, the "LOL" chart. The "LOL" chart contains two energy bar graphs, one before and one after the energy transfer, and one system bubble in the center, creating the acronym LOL. Oftentimes, if work is transferred into or out of the system, an arrow will either go in or out of the system bubble, with the indicated type of work. The number of squares, which signify amounts, must be equal to each other because energy is conserved. An energy conservation equation is also used to show the different types of energy before and after the transfer.
Energy Problem Solving
In order to solve an energy problem, the first step is to make a LOL chart identifying the different types of energy before and after the transfer. There are five types of energy: elastic potential, gravitational potentional, kinetic energy, internal potential energy, and chemical energy. Elastic potential energy is the energy stored in an elastic material by stretching or compressing it. Gravitational potential energy is the potential energy created from gravity stored in the Earth's gravitational field. Kinetic energy is the energy stored in moving objects. Internal potential energy is the energy stored within the system, typically in heat, within the atoms of the system. With these types of energy in mind, you create a LOl graph. With your conservation of energy equation, you apply one or more of the four formulas to your problem to solve it.
Work
Energy is neither created nor destroyed. therefore, most losses or increases of energy are due to transfers. In order to transfer this energy, work must be done to the system. There are three types of energy transfers: working, heating, and radiating. Working energy transfers (W) are an external push or pull on a system. Heating energy transfers (Q) are through temperature and the average amount of kinetic energy between two objects. For example, if a warmer object transfers energy to a cooler one, the temperature will average out depending on the amount of energy transferred. Radiating energy transfers (R) are when matter loses energy by radiating light and gains energy when absorbing light.
Power
Power is the rate of change of energy or the rate of doing work. Power is measured in watts (W), which is equal to 1 J/s. A horsepower is a unit of power equal to 550-foot pounds per second.
Connecting Energy/Work/Force to Motion
Energy transfers due to working energy are not possible without motion, as a working energy transfer is due to an external push or pull, which is a type of force. This energy transfer is work, which is, in turn, a force that causes an energy transfer.
Connecting Representations of Motion to Representations of Forces to Representations of Energy
If the force is an external working force, then usually the more motion, the stronger the force. This will either cause a greater or lesser increase in energy depending on if the energy is traveling into the system or out of the system. The energy must be working energy for this to work because other transfers of energy are not in motion.