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You are watching: Why does gas expand when heated

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Expansion and Contraction : Why does heat and cold make things expand and contract ? Also why do some metals expand more than others? Asked by: Marcus MckeanAnswerRecall that all materials are made up of atoms. At any temperature above absolute zero (-273 degreescelsius) the atoms will be moving. In a solid they will be vibrating in fixed positions, ina liquid thy will be jostling past each other and in a gas they will be whizzing past eachother at very high speeds. When a material is heated, the kinetic energy of that material increases andits atoms and molecules move about more. This means that each atom will take up more space due to its movement sothe material will expand. When it is cold the kinetic energy decreases, so the atoms take up less spaceand the material contracts. Some metals expand more than others due to differences in the forces between the atoms / molecules. In metalssuch as iron the forces between the atoms are stronger so it is more difficult for the atoms to moveabout . In brass the forces are a little weaker so the atoms are free to move about more. Thesedifferences in contraction are used in a bimetallic strip, which is composed of a strip of brasslaid along side strip of Iron. When the strip is heated the brass expands more than the iron so thestrip beds. It is used in devics such as fire alarms and circuit breakers to either make or breakcontacts in an electric circuit. The differences in expansion and contraction are even more visible in different states, again due tothe amount of force holding the atoms together. A gas will expand the most as its atoms are freefrom each other so are free to increase in speed the most.Answered by: Sara Al-Assam, Student, Tiffin Girls" School, Kingston
"Beauty is a harmonious relation between something in our nature and the quality of the object which delights us."Blaise Pascal(1623-1662)


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