Physical Science 8th grade (1).pdf

Meteor a chunk of burning rock traveling through

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meteor – a chunk of burning rock traveling through Earth’s atmosphere. meteorite – a meteor that passes through Earth’s atmosphere and strikes the ground. mixture – a substance that includes more than one type of element and/or compound. molecule – a group of atoms held together by covalent bonds in a specific ratio and shape. mutation – change in the sequence of base pairs in DNA that may be passed on to successive generations. N natural law – the set of rules that are obeyed by every detail of everything that occurs in the universe, including living creatures and human technology. nebula – a huge cloud of dust and gas from which stars form. net force – the sum of two or more forces on an object. neutral – a condition where the total positive charge is canceled by the total negative charge. Matter is neutral most of the time. neutron – a particle with zero charge found in the nucleus of atoms. newton (N) – the unit of force in the metric (SI) system. Newton’s first law – an object at rest will stay at rest and an object in motion will stay in motion with the same velocity unless acted on by an unbalanced force. Newton’s law of universal gravitation – the force of gravity between objects depends on their masses and the distance between them. Newton’s second law – acceleration is force ÷ mass. Newton’s third law – for every action force, there is a reaction force equal in strength and opposite in direction. noble gases – elements in the group containing helium, neon, and argon, among others. nonmetal – elements that are poor conductors of heat and electricity. normal force – the force a surface exerts on an object that is pressing on it. nuclear reaction – a process that changes the nucleus of an atom and may turn one element into a completely different element. nucleic acids – biological molecules such as DNA that have the ability to store the genetic code. nucleus – the tiny core at the center of an atom containing most of the atom’s mass and all of its positive charge.
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372 O objective – describes evidence that documents only what actually happened as exactly as possible. orbit – the motion of one object around another caused by gravitational force. organic chemistry – the chemistry of carbon and carbon compounds. origin – a fixed reference point. oxidation number – indicates the charge of an atom when an electron is lost, gained, or shared in a chemical bond. An oxidation number of +1 means an electron is lost, -1 means an electron is gained. P period – a row of the periodic table is called a period. periodic table – a chart that organizes the elements by their chemical properties and increasing atomic number. periodicity – the repeating pattern of chemical and physical properties of the elements.
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