Physical Science 8th grade (1).pdf

Friction a force that resists the motion of objects

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friction – a force that resists the motion of objects or surfaces. G galaxy – a group of stars, dust, gas, and other objects held together by gravitational forces. gas planets – Jupiter, Saturn, Uranus, and Neptune. gram (g) – a unit of mass smaller than a kilogram. One kg equals 1,000 g. graph – a mathematical diagram showing one variable on the vertical ( y ) axis and the second variable on the horizontal ( x ) axis. group – a column of the periodic table is called a group. H halogens – elements in the group containing fluorine, chlorine, and bromine, among others. heat – thermal energy that is moving. heat conduction – the transfer of heat by the direct contact of particles of matter. hypothesis – an unproven or preliminary explanation that can be tested by comparison with scientific evidence. Early hypotheses are rarely correct and are often modified as new evidence becomes available. I independent variable – in an experiment, a variable that is changed by the experimenter and/or causes changes in the dependent variable. inertia – the property of an object that resists changes in its motion. inquiry – a process of learning that starts with questions and proceeds by seeking the answers to the questions. insoluble – a substance is insoluble in a particular solvent if it does not dissolve in that solvent. insulator – a material that slows down or stops the flow of either heat or electricity. intermolecular forces – forces between separate atoms and molecules that are attractive at a distance but repulsive at close range. ion – an atom that has an electric charge different from zero. Ions are created when atoms gain or lose electrons. ionic bond – a bond that transfers an electron from one atom to another resulting in attraction between oppositely charged ions. isotopes – atoms of the same element that have different numbers of neutrons in the nucleus. J joule (J) – the unit of energy in the metric (SI) system. One joule is enough energy to push with a force of one newton for a distance of one meter. K kilogram (kg) – the basic metric (SI) unit of mass. L light year – the distance light travels in one year (9.5 trillion km). luminosity – the total amount of light given off by a star.
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371 Glossary M magnitude – describes the size component of a vector. main sequence star – a stable star in the main category in the H-R diagram. mass – the amount of matter an object contains. mass number – the number of protons plus the number of neutrons in the nucleus. matter – everything that has shape and takes up space. melting point – the temperature at which a substance changes from a solid to a liquid. metal – elements that are typically shiny and good conductors of heat and electricity.
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