3.3 Density, Temperature, and Buoyancy

RECALL. . . Viscosity How viscosity changes with temperature Density D = m/v Does density also change when the temperature changes?

The Particle Model as an Explanation for Density Changes Textbook summary notes Particles in a substance move more quickly when energy is added. As a solid changes to a liquid, then to a gas, the particles move faster and faster. As particles become more active, the space between them increases. The Volume increases, but the number of particles stays the same.

How can we simplify this? As temperature increases …. Particles gain energy  they will move faster  the spaces in between the particles will increase. It is this increase in the spaces between the particles that will decrease the density. Because now you will have less particles in the space it occupies. Your textbook explains this as.. The Volume increases, but the number of particles stays the same.

Different Temperature, Different Density As a substance is heated, it changes state. A substance (except water) has a greater density in its solid state then in its liquid and gas states. One substance, can have different densities depending on its temperature.

Changing Density by Changing Concentration pg. 49 Density depends on the number and kind of particles in a given volume. Dissolving one substance in another increases the number of particles in a given volume. By adding more particles (increasing the concentration), the density increases.

BUOYANCY Buoyancy is the tendency of an object to float when placed in a fluid. The buoyant force is the force in fluids that acts against gravity. Neutral buoyancy

Buoyancy is an important factor in some transportation technologies Ships (plimsoll line) Hot air balloons

BUOYANCY pg. 50 When an object is in a liquid, the force of gravity pulls it down. The liquid, exerts an opposite force, the buoyant force, that pushes the object upward. If the buoyant force is greater than the force of gravity, the object will float. If the force of gravity is greater than the buoyant force, the object will sink.

Plimsoll Line pg. 51 The Plimsoll Line indicates how heavily loaded a ship can be in different densities of water. As the air in a hot air balloon is heated, the air becomes less dense than the surrounding air. The buoyant force pushes the balloon up.

Your Homework: Section 3.3 Handout