GED Science Study Guide: Physical Science

Physical science is the study of how inanimate (i.e. nonliving) things exist and interact in nature. In this section, we’ll explore the following topics:

• Astronomy
• Chemistry
• Physics

Practice Quiz

Astronomy

Astronomy is a branch of science focusing on celestial objects (i.e. everything in space), space itself, and the universe.

We already covered a few astronomy topics by discussing the Solar System in the previous section. Here, we’ll explore everything beyond Neptune, the farthest planet from the Sun.

The Solar System is part of the Milky Way Galaxy, a slowly rotating disc containing 100-400 billion stars. That may seem impressive, but the Milky Way is only one of hundreds of billions of galaxies that make up the Universe – the entirety of space and everything in it.

Scientific advances in the 20th century helped astronomers make significant discoveries about the universe. The fact that all the galaxies are moving away from one another suggests that a Big Bang created all the matter in the universe. Why this Big Bang happened or what caused it is still a mystery. However, we do know that this Big Bang happened about 13.8 billion years ago.

Here are a few astronomy terms you should know going into the GED science test:

• Asteroid: A lump of rock or metal floating through space.
• Black Hole: An area of intense gravity that sucks everything into it, even light.
• Comet: A ball of rocky ice. Comets make tails in the sky because heat from the Sun turns the ice into water vapor.
• Constellation: A pattern of stars in the sky. Constellations’ names date back hundreds or thousands of years.
• Meteor: An asteroid as it falls through Earth’s atmosphere. Many small meteors burn up due to the intense friction with the air.
• Meteorite: What remains of a meteor once it hits the Earth. Studying meteorites can tell scientists much about the early Solar System.
• Supernova: The implosion of an old, massive star. Supernovae are visible from tens of thousands of light-years (the distance it takes light to travel in a year) away.

Chemistry

Chemistry is a branch of science focusing on matter (i.e. stuff) and how matter interacts.

Matter typically exists in one of three states:

• Gas (e.g. water vapor)
• Liquid (e.g. liquid water)
• Solid (e.g. ice)

The temperature at which matter turns from one state to another depends on the strength of its molecular bonds. Most metals have very high melting points because their bonds are very strong.

Chemists organize elements using the periodic table.

Source: Sandbh, CC BY-SA 4.0, via Wikimedia Commons

The periodic table organizes elements by what makes certain elements similar. For example, the noble gases (Group 18) are all colorless gases that do not react with other elements.

Elements can create compounds with other elements through chemical reactions. One notable example is when chlorine (a poisonous gas) and sodium (a metal that explodes on contact with water) react, they produce harmless and tasty table salt.

Chemical reactions like the one below must always be balanced, meaning that both sides of the equation must have the same number of atoms.

Source: JyntoRobert A. RohdeJacek FHJynto, Public domain, via Wikimedia Commons

In this equation, one methane (CH4) molecule reacts with two oxygen (O2) molecules to produce one carbon dioxide (CO2) molecule and two water (H2O) molecules.

This is a dramatic reaction, as methane and oxygen will burn in the presence of a flame. The methane and oxygen are reagents, and the carbon dioxide and water are products. The law of the conservation of matter states that chemical reactions, no matter how dramatic, cannot destroy atoms. As a result, both sides of an equation must be balanced.

Many chemistry experiments involve creating solutions – a mix of two or more things. Saltwater is a simple solution. In it, the water is the solvent, the thing something dissolves into. The salt is the solute, the thing that dissolves into the solvent. However, in a solution, no chemical reaction takes place. If you boiled a pot of saltwater, the water would turn to steam, leaving the salt in the pan.

Physics

Physics is the branch of science that studies the underlying laws and mechanisms that show how the universe works, from the biggest stars to the smallest atoms.

To start our journey, we need to return to the humble atom.

Source: AG Caesar, CC BY-SA 4.0, via Wikimedia Commons

An atom is the smallest part of any element. It contains a few important parts you should know for the GED science test.

• Nucleus: The center of the atom containing protons and neutrons.
• Proton: A positively charged subatomic particle. An atom’s number of protons determines its atomic number on the periodic table.
• Neutron: A subatomic particle with no electric charge. Every element besides hydrogen has them.
• Electron: A negatively charged subatomic particle that orbits the nucleus. Chemical reactions cause atoms to share or exchange electrons.

Two atoms that are the same element (i.e. have the same number of protons) can have different numbers of neutrons. This discovery led scientists to adopt the word isotope to describe these differences. For example, the most abundant carbon isotope in nature (like that in your pencil graphite) is carbon-12, meaning 12 neutrons. However, some carbon is carbon-14, meaning 14 neutrons. Because carbon-14 is somewhat unstable, it releases energy in the form of mild radiation.

Radiation refers to the emitting of energy. Not all radiation is the same. You feel the warm solar radiation every time you walk outside. Some radiation is harmful because it can damage or kill our cells.

Remember the last section, when we discussed the law of the conservation of matter? There is an extra piece of information you should know. Although matter can’t be destroyed, it can be turned into energy. This is what happens in nuclear fission – splitting unstable atoms apart. The number of atoms that split is the difference between a nuclear power plant (controlled splitting) and a nuclear bomb (uncontrolled splitting).

Physical laws guide how matter interacts. Some of the oldest are Sir Isaac Newton’s (1643-1727) Laws of Motion:

• First Law: Objects will remain at rest unless acted upon by something else.
• Second Law: The rate of change is equal to the force (e.g. a push or pull) applied to something.
• Third Law: For every action, there is an equal and opposite reaction.

Physicists also study fundamental forces.

Physical Science Review Quiz