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What determines the phase of matter for a substance like water? The phase of water depends on two factors: temperature and pressure.
We all know and care about temperature. We often check the weather report to see whether or not we need a coat. We use thermometers to measure temperature in either degrees Celsius (°C) or Fahrenheit (°F).
Water changes from a liquid to a gas, a solid to a liquid, or a liquid to a solid at different temperatures known as boiling points, melting points, and freezing points.