The Physics
Hypertextbook
Opus in profectus

# Simple Machines

## Problems

### practice

1. A bucket grain elevator is powered by a 150 kW electric motor. Determine its efficiency if it can lift grain to a height of 60 m at a rate of 900 m3/h. Assume the elevator is lifting wheat with a density of 770 kg/m3.
2. Write something else.
3. Write something different.
4. Write something completely different.

### statistical

1. The United States in a humongous machine. Energy comes in, energy goes out, and work is done. Every year since 1976 (and a for a few years before that), the Lawrence Livermore National Laboratory (LLNL) has released annual flowcharts that illustrate the production and consumption of energy for the whole of the United States. Primary energy sources are on the far left (petroleum, natural gas, coal, nuclear, biomass, wind, hydro, solar, geothermal) Energy consumption sectors are on the near right (transportation, industrial, residential, commercial) with electricity generation as an intermediate step. Ultimately, all energy winds up on the far right as useful energy (energy services) or rejected energy (lost energy).

The images below link to a copy of every LLNL energy flowchart I could find. Use the information in these flowcharts to create four time series graphs for the US machine and comment briefly on each one. The overall trend in one graph may shock you.
1. energy consumption vs. year
2. useful energy vs. year
3. rejected energy vs. year
4. efficiency vs. year
Some notes for people who like to know stuff. First, although LLNC produces these diagrams, the data used to produce them comes from the US Energy Information Agency (EIA). In a sense, the EIA provides the statisticians and the LLNC provides the artists. Second, the EIA is an American institution and America still has a ways to go when it comes to the International System of Units. Energies are reported in quads instead of joules or multiples of a joule. A quad is a quadrillion British thermal units (Btu). A Btu is the energy needed to raise one pound of water by one degree Fahrenheit (°F) and a quadrillion is one followed by 15 zeros (1015). For comparison: US gallon of gasoline has about 100,000 Btu (105 Btu) of chemical energy, and a US toaster uses about 100 Btu (102 Btu) of electrical energy in the two minutes it takes to toast two slices of bread. For simplicity sake, a quad is almost the same as an exajoule (1018 J). The exact conversion doesn't matter since this is a question about trends. If you have an aversion to non-SI units, then just replace every mention of a quad with an exajoule. It won't affect the trends in the data.