Expansion and Contraction

 As the average energy of particles increases, the spaces between the particles increases. They expand (increase their volume) as the temperature increases. As the average energy of particles decreases, the spaces between the particles decreases. They contract (decrease their volume) as the temperature decreases.

Expansion and Contraction in Solids  Solids can become longer or shorter depending on the temperature (average energy of the particles).

Expansion and Contraction in Liquids  When the particles in a liquid are heated, their average energy increases and they need more room, so they expand. When the particles in a liquid are cooled, the volume decreases, or contracts, because the particles need less room. This is demonstrated by the liquid used in a thermometer. As the liquid expands and contracts, it moves up and down the inside tubing ( the bore ) of the thermometer.

Expansion and Contraction in Gases  When the particles in a gas are heated, their average energy increases and they need more room, so they expand.  When the particles in a gas are cooled, the volume decreases, or contracts, because the particles need less room.  Under extremely high temperature conditions (like the temperatures inside the Sun, particles can be split into what makes them up (electrons and ions). This creates a fourth state of matter called plasma.

Pre Quiz  If you were to carefully measure the width of cracks in the sidewalk at many different times during a two-year period, which would you expect to find? a. The cracks would remain the same size throughout the time. b. The cracks would be wider during winter than during the summer. c. The cracks would be wider during the summer than during the winter. d. The cracks would continue to widen as time passes.

Pre Quiz  A railroad track was built with all of the rails fitting tightly together, touching each other end- to-end. Six months later, the track was ruined when the rails expanded and buckled. What may have caused the rails to expand? a. As the weather got warmer, the particles in the rails moved more slowly. b. As the weather got colder, the particles in the rails moved more slowly. c. As the weather got warmer, the particles in the rails moved faster. d. As the weather got colder, the iron in the rails froze.

Pre Quiz  One of the best ways to weaken the bonds holding particles together is by a. heat b. grinding c. movement d. pressure

Pre Quiz  A metal lid was very tightly screwed onto a glass jar. To get the jar open, Kelly held the lid under hot water. Why was Kelly able to remove the lid? a. Metal particles move more rapidly when heated so the particles moved further apart, and the lid became looser. b. Metal particles move less rapidly when heated so the particles moved closer together, and the lid became looser. c. The metal particles did not move. The water loosened the lid. d. The metal particles melted because the water was so hot.

Pre Quiz  The teacher heats the steel ball over a Bunsen burner and then tries to put the steel ball through a ring that it fit through when it was cold. Based on what you know about the relationship between temperature and motion of particles, choose the best explanation for this experiment. a. The steel ball will fit because it was heated, causing the molecules to contract. b. The steel ball will not fit because it was heated, causing the molecules to expand. c. The steel ball will fit because it was cooled, causing molecules to expand. d. The steel ball will not fit because it was cooled, causing the molecules to contract.

Pre Quiz  The Golden Gate Bridge is a suspension bridge constructed with steel and concrete. Measurements are taken daily on various joints along the surface of the bridge. At 7 a.m., joint 1 has a measurement reading of 13 cm. At 3 p.m., the same joint has a reading of 6 cm. Give a reasonable explanation to explain this occurrence.

Steel Bridges  Have expansion joints.

Bridge Expansion Joint Example

Railroad Tracks  Have gaps at each joint.

Railroad Rails

Concrete roads  Have expansion joints built in.

Concrete Roads

Sidewalks  Sidewalks are built with expansion joints to try and avoid the cracking that may occur.  Sometimes a sidewalk will develop a crack even with expansion joints. Do you know what happens to the size of the cracks in the winter and summer?

Sidewalks

Cars  Cars have engines with many working parts. The parts are engineered to be a little loose when cold so that when the engine becomes warm the parts do not expand to be to tight.

Post Quiz 1. Molecules are in constant motion. TrueFalse

Post Quiz 2. Molecules get farther apart because a. Energy is added b. Energy is taken away c. Molecules can’t get farther apart d. Molecules are taken away from the substance.