Matter & Energy


Matter is composed of atoms or groups of atoms called molecules. The arrangement of particles in a material depends on the physical state of the substance. In a solid, particles form a compact structure that resists flow. Particles in a liquid have more energy than those in a solid. They can flow past one another, but they remain close. Particles in a gas have the most energy. They move rapidly and are separated from one another by relatively large distances.

Passive Solar Heating

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The solar energy that falls naturally on a building can be used to heat the building without special devices to capture or collect sunlight. Passive solar heating makes use of large sun-facing windows (south-facing in the Northern Hemisphere) and building materials such as brick and tile that absorb and slowly release solar heat. A designer plans the building so that the longest walls run from east to west, providing lengthy southern exposures that allow solar heat to enter the home in the winter. A well-insulated building with such construction features can trap the Sun’s energy and reduce heating bills as much as 50 percent. Passive solar designs also include natural ventilation for cooling. Shading and window overhangs also reduce summer heat while permitting winter Sun.

In direct gain, the simplest passive heating system, the Sun shines into the house and heats it up. The house’s materials store the heat and slowly release it. An indirect gain system, by contrast, captures heat between the Sun and the living space, usually in a wall that both absorbs sunlight and holds heat well. An isolated gain system isolates the heated space (a sunroom or solar greenhouse, for example) from the living space and allows the solar heat to flow into the living area via convective loops of moving air.