the international system of units (si) is a revision of the 1. system. there are 2. si base units. in si, the base unit of length is the 3.
the space taken up by a cube that is 10 cm on each edge is one 4. a measure of the pull of gravity on an object of given mass is its 5. the mass of one cubic centimeter of water at 4°c is one 6. scientists commonly use two equivalent units of temperature, the degree 7. and the the 9. and the 10. are common units of energy.

Achemical reaction (also known as a chemical change) produces substances that are chemically different from the starting materials. an example of a chemical reaction is the formation of water from hydrogen and oxygen gas. in a physical change, a substance changes its physical appearance but not its chemical identity. an example of physical change is the formation of liquid water from solid water, a familiar process called melting. physically, liquid water looks very different from solid water (ice) but the chemical identity, water, is the same for both. which of following changes that affect the composition of our atmosphere involve physical changes and which involve chemical reactions? oxygen gas changes to ozone during thunderstorms carbon dioxide is produced by the combustion of gasoline in an automobile engine. when coal, oil, and natural gas are decomposed in landsills they produce methane gas. freezing rain develops when a warm air mass overrides a cold air mass. fog forms from water vapor when the temperature drops below the dew point

Why are people not able to scuba dive in the deep part of the ocean

Sally is making a model of a magnesium atom with an atomic mass number of 24 for her chemistry class. she has foam balls for the protons, neutrons, and electrons. she has added 6 neutrons to her model so far. how many more neutrons does she need to add to complete her neutral atom of magnesium?