Follow energy through a system and distinguish a source from an energy form.
Kinetic energy is associated with motion. Gravitational potential energy depends on position in a gravitational field. Elastic potential energy can be stored when a spring or band is deformed. A moving mechanism can transfer energy between these stores and its surroundings.
For a battery-powered motor lifting a load, chemical energy is transferred electrically to the motor, then mechanically to the load. The load gains gravitational potential energy; the motor and surroundings also warm.
Wind, flowing water, sunlight, fuels and food can supply energy to a system. Renewable resources can be replenished on human time scales under suitable management. Non-renewable fuels are consumed much faster than they form. Neither label means impact-free.
Energy does not disappear when a mechanism slows. Friction can increase thermal energy in the parts and surroundings. A diagram showing only useful motion leaves out part of the account.
Open Systems. Connect a source, a converter and a user. Turn on energy symbols. Try the bicycle and generator, then compare another source. Follow both useful transfers and heating.
The symbols are a model for tracking energy; they are not particles of a substance. An unsuitable source–converter combination may not operate.
TED-Ed · Mechanism in action
Follow one transformation. Explain why energy can move between stores and surroundings without being created by the machine.
Where does the energy go when a skater slows because of friction?
Some kinetic and gravitational potential energy becomes thermal energy in the skater, track and surroundings. Total energy is conserved for a sufficiently complete account.
Build two source–changer–user chains. Explain why a source may work well with one converter but not another.
Apply it to the design challenge →Read further: OpenStax · Simple Machines →
