1. Newton
   Joule
2. Meters per second
   Planks

Force is a push or pull on an object. Scientists measure the strength of these forces in Newtons. You might be more familiar with the unit "pounds," which measures how much something weighs. Fun fact: 1 Newton is approximately 0.224809 pound-force!

1. Acceleration
   Speed
2. Inertia
   Reaction

A car is a good illustration of some different types of acceleration. When we hit the gas, the car speeds up, and when we turn the wheel, the car travels in a new direction. When brakes are applied, the car slows down, which is an example of negative acceleration.

1. Baryonic matter
   Plasma
2. Dark matter
   Quarks

About 80% of the universe is made up of materials that are not observable by scientists, Known as dark matter, it exists in order to hold the elements of the universe together.

1. Kilogram
   Scale
2. Weight
   Acceleration

The weight of an object changes with the strength of gravity. The acceleration due to gravity on Earth is 9.8 m/s/s. Someone with a 60kg mass on Earth weighs about 132 pounds. That same person would weigh about 21 pounds on the moon, due to smaller gravitational pull.

1. Ion
   Molecule
2. Atom
   Dendrite

Scientists once thought the atom was the smallest measurable substance on Earth. They now have discovered that the atom is made up of even smaller particles including protons, neutrons and electrons.

1. Quark
   Ion
2. Isotope
   Neutrino

An ion is an atom that has either gained or lost electrons. Since electrons are negatively charged, an atom that has lost an electron has a positive charge, while an atom that has gained an electron has a negative charge.

1. Estuary
   Continent
2. Ecosystem
   Delta

An ecosystem includes all of the living and non-living things in a particular environment. The Earth contains many types of ecosystems, ranging from large areas such as the Siberian tundra to the puddle in your backyard.

1. Riboflavin
   Amino acid
2. Mineral
   Enzyme

Enzymes are typically proteins that speed up reactions that take place in cells. Some enzymes help break down larger molecules, and others bind molecules. All enzymes are highly selective and only help speed up specific reactions.

1. Interaction between objects
   Something that holds an object in place
2. Amount of energy an object has
   Measure of mass

Force is a push or pull on an object that causes an acceleration. This can include making an object start moving, stop moving, speed up, slow down or change directions. Examples of forces include: gravitational, magnetic, friction, applied and elastic.

1. Motion
   Weight
2. Mass
   Bulk

Mass is measured in grams, and this measurement remains the same regardless of an object's location in the universe. If you have a mass of 75kg on Earth, you will also have a mass of 75kg on the moon. Gravity does not affect mass.

1. Metabolism
   Regeneration
2. Respiration
   Photosynthesis

Photosynthesis is the process of converting carbon dioxide into glucose. Animals must consume glucose, but plants have the unique ability to create their own. The glucose is used in various metabolic processes in most living things.

1. Symbiotic
   Communalism
2. Sociology
   Biodiversity

Mutualism, commensalism and parasitism are all types of symbiosis. Mutualism has benefits for both species involved, while commensalism benefits one part but does no harm to the other. Parasitism benefits one species while causing harm to the other.

1. Ribosome
   Prokaryotic
2. Eukaryotic
   Volvox

Humans are eukaryotic organisms. Our cells contain membrane-bound organelles such as mitochondria, the Golgi apparatus and ribosomes. Each organelle has a different job within the cellular system.

1. Family
   Genus
2. Kingdom
   Class

There are five kingdoms in the eukaryotic domain: monera, protists, fungi, plants and animals. Each kingdom can be further divided into the categories of phylum, class, order, family, genus and species.

1. Anion
   Argon
2. Cation
   Isotope

Most of the property of an atom comes from the number of protons and electrons, with neutrons still playing a part. The neutron has an impact of the mass of an atom, and some isotopes are more radioactive than others.

1. Rodinia
   Gondwana
2. Pangea
   Tectonics

The breakup of a large super continent known as Pangea helped scientists establish the modern theory of plate tectonics. It is thought that the Earth's outer shell is made up of several plates that slide over the mantle.

1. Mitosis
   Meiosis
2. Binary fission
   Budding

Mitosis is the primary mechanism organisms use to reproduce cells. In the eukaryotic cell, this process has five phases: interphase prophase, metaphase, anaphase and telophase. These phases produce the two identical daughter cells.

1. Budding
   Binary fission
2. Meiosis
   Mitosis

The end goal of meiosis is to produce four daughter cells with genetic variation. Meiosis involves two rounds of nuclear division rather than just one. Variation is further increased when two gametes meet during fertilization.

1. Momentum
   Power
2. Propulsion
   Thrust

Momentum is the product of mass and velocity. A large bus traveling at 60 mph has more momentum than a Prius traveling at 15 mph. A head-on collision of these two objects would cause considerable damage to the Prius, because the change in momentum would be greater with the Prius.

1. Dianetics
   Cybernetics
2. Homeostasis
   Oscillation

The human body uses a number of homeostatic processes. Humans maintain a normal body temperature by sweating when too warm and shivering when too cold. We must also maintain homeostasis in regards to pH levels and blood pressure.

1. Strong force
   Weak force
2. Gravity
   Magnetism

Gravity is the force that brings you back to the ground when you jump, and it also keeps the Earth in orbit around the sun. Gravity is a product of an objects mass. This is why a person weighs more on Earth than they would on the moon, which has a much smaller mass than Earth.

1. Compound
   Molecule
2. Element
   Ion

The periodic table of elements, like the one seen in science classes, lists all the elements known to humankind. Each one is defined by a set of unique characteristics, including the number of protons and its inclination to interact with other elements.

1. Sound energy
   Potential energy
2. Electrical energy
   Thermal energy

An object has potential energy if it has the possibility of motion. Examples of potential energy are: gravitational, elastic, chemical and nuclear. Potential energy can move to kinetic energy and back again. A classic example of this would be a roller coaster.

1. Mantle
   Crust
2. Core
   Outer core

The mantle is mostly a solid layer of Earth. It lies between the molten core and the outer crust. It's the thickest layer, making up about 84% of the Earth's volume, at almost 2,000 miles thick.

1. Haploid
   Genome
2. Chromosome
   Cell

Your genome contains the instructions for all of your human characteristics, written in a chemical code known as DNA. Human DNA contains around 20,000 genes. Each of these genes are specific instructions for making proteins, the building blocks of our body.

1. Potential energy
   Gravitational energy
2. Kinetic energy
   Magnetic energy

Kinetic energy is a product of an object's mass and velocity. The faster an object travels, the more kinetic energy it has. The more kinetic energy an object has, the more work it can do.

1. Energy conservation
   Velocity
2. Reaction
   Inertia

Inertia is an object's tendency to continue doing what it is doing unless acted upon by a force. If not for friction, a ball's inertia would keep it rolling forever. Earth's inertia keeps it revolving around the sun.

1. Genotype
   Phenotype
2. Allele
   Chromosome

Each person inherits two alleles for each gene, one from each parent. These various alleles give rise to all physical traits such as eye and hair color. Some alleles are more dominant than others. The combination of alleles is called the genotype, and the physical trait expressed is called the phenotype.

1. Light-year
   Astronomical unit
2. Mile
   Nebula

A light-year is the distance light travels in one year. This is roughly equal to 6 trillion miles. The Earth is about 8 light-minutes from the sun and 4.3 light-years away from the next closest start, Proxima Centauri.

1. Covalent bond
   Fission
2. Ionic bond
   Fusion

Fusion occurs when wo atoms fuse together to create a single new atom. This new atom contains less mass than the two previous atoms combined. This missing mass is given off in the form of energy as described in Einstein's equation E=mc^2. This is the main source of energy for the sun.

1. Rubber
   Insulator
2. Conductor
   Magnets

Conductors can be metal, solutions and even the human body. The only requirement for a conductor is they allow electrons to flow freely. Some of the most conductive materials include silver, copper and aluminum.

1. Velocity, acceleration and jerk
   Snap, crackle and pop
2. Mass, volume and density
   Neutrino, quark and spin

Velocity describes the rate at which position changes. Accelerations describes the rate at which velocity changes. Scientists can analyze further derivatives of position including snap, crackle and pop, each describing how the previous derivative changes.

1. Somatic cells
   Sex cells
2. Stem cells
   Blood cells

Stem cells have the potential to develop into any type of cell. It has huge medical implications because it allows for the creation of any kind of tissue. Stem cells can be found in an embryo's bone marrow and in the umbilical cord.

1. Sedimentary
   Metamorphic
2. Igneous
   Granite

Igneous is the type of rock formed when liquid magma cools and solidifies. The most common type of igneous rocks are basalt, obsidian and pumice. The variety comes from the different chemical composition of magma.

1. Zygote
   Gamete
2. Ovum
   Embryo

A zygote is a single-cell organism resulting from the unification of a sperm and egg cell. A zygote will continue to divide until it becomes a blastocyst, at which point it will implant in the wall of the uterus. This will eventually develop into an embryo and then a fetus.