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Greenhouse gases Gases
such as carbon dioxide and
methane that absorb energy
reflected by Earth’s surface,
stopping it from escaping
into space.
Heat death A possible end state
for the universe in which there are
no temperature differences across
space, and no work can be done.
Heliocentrism A model of the
universe with the Sun at its center.
Higgs boson A subatomic particle
associated with the Higgs field,
whose interaction with matter
gives matter its mass.
Hydrocarbon A chemical whose
molecules contain one of many
possible combinations of hydrogen
and carbon atoms.
Ion An atom, or group of atoms,
that has lost or gained one or
more of its electrons to become
electrically charged.
Ionic bond A bond between two
atoms in which they exchange an
electron to become ions. The ions’
opposite electric charge attracts
them to each other.
Leptons Fermions that are
affected by all of the four
fundamental forces except
the strong nuclear force.
Magnetism A force of attraction
or repulsion exerted by magnets.
Magnetism is produced by
magnetic fields or by the property
of magnetic moment of particles.
Mass A property of an object
that is a measure of the force
required to accelerate it.
Mitochondria Structures
within a cell that supply energy
to the cell.Molecule The smallest unit
of a compound that has its
chemical properties, made of
two or more atoms.Momentum A measure of the
force required to stop a moving
object. It is equal to the product of
the object’s mass and its velocity.Multiverse A hypothetical set of
universes in which every possible
event happens.Natural selection The process
by which characteristics that
increase an organism’s chances
of reproducing are passed on.Neutrino An electrically neutral
subatomic particle that has a
very small mass. Neutrinos
can pass right through
matter undetected.Neutron An electrically neutral
subatomic particle that forms part
of an atom’s nucleus. A neutron is
made of one up-quark and two
down-quarks.Nucleus The central part of an
atom, comprising protons and
neutrons. The nucleus contains
almost all of an atom’s mass.Optics The study of vision and
the behavior of light.Organic chemistry The chemistry
of compounds containing carbon.Parallax The apparent movement
of objects at different distances
relative to each other when an
observer moves.Particle A tiny speck of matter
that can have velocity, position,
mass, and charge.Pauli exclusion principle
In quantum physics, the principle
that two fermions (particles with
mass) cannot have the same
quantum state in the same point
in space-time.Periodic table A table containing
all the elements arranged according
to their atomic number.Photoelectric effect The
emission of electrons from the
surfaces of certain substances
when light hits them.Photon The particle of light that
transfers the electromagnetic force
from one place to another.Photosynthesis The process by
which plants use the energy of the
Sun to make food from water and
carbon dioxide.Pi (π) The ratio between the
circumference of a circle and its
diameter. It is roughly equal to
22/7, or 3.14159.Pi bond A covalent bond in which
the lobes of the orbitals of two or
more electrons overlap sideways,
rather than directly, between the
atoms involved.Plate tectonics The study of
continental drift and the way in
which the ocean floor spreads.Polarized light Light in which the
waves all oscillate in just one plane.Polymer A substance whose
molecules are in the shape of long
chains of subunits called monomers.GLOSSARY