3.2 Density of Fluids

Review: Particle Model of MAtter 4 main points: All matter is made up of tiny particles The tiny particles of matter are always moving and vibrating http://www.harcourtschool.com/activity/states_of_matter/ The particles in matter may be attracted to each other or bonded together The particles have spaces between them

Review: Viscosity is how quickly a fluid flows It is determined by a fluids internal resistance or friction that keeps it from flowing The greater the friction or rubbing between particles in any FLUID (liquids or gas), the higher the viscosity Fluids with high viscosity do not flow as easily As the temperature of a fluid increases, it’s viscosity decreases We can measure viscosity using the ramp method. http://www.planetseed.com/laboratory/viscosity-explorer

Density Not all substances have the same density Usually, the greater the viscosity., the greater the density Density is the amount of matter in a given volume and can also be defined as the mass per unit volume of a substance In other words, density is mass divided by volume. Mass is the amount of matter in an object and is measured in grams or kilograms Volume is the amount of space occupied by an object. It is measured in cubic units such as cm3

3.3 Density, Temperature and Buoyancy If viscosity changes with temperature…does density?

The Particle Model as an explanation for density Changes Yes! According to the particle model, particles in a substance move more quickly when energy is added. As a solid changes to a liquid and eventually a gas, the particles move faster and faster As particles become more active, they move away from each other and the space between them increases This will cause the volume to increase, but the number of particles will stay the same With the same number of particles in a larger volume, the density decreases Remember that density is the ratio of mass to volume

Different temperature, Different density If a substance is either heated or cooled, it will change state! If you heat a substance up it will become a liquid (or gas at even higher temperatures) If you cool down a substance it will become a solid A substance (except water) has a greater density in its solid state than its liquid and gas state

Changing Density by changing concentration Concentration: the amount of solute dissolved in a specific amount of solvent in a solution; written g/ml or kg/L Remember that density depends on the number and kind of particles in a given volume If we took salt and added it to water what would happen?

By adding more particles (salt) we would be increasing the density of the water solution Increasing the concentration of salt in the solution increases the density. Conclusion: Less dense objects float in more dense substances!

Other factors that affects floating; Buoyancy! When an object is in a liquid, the force of gravity pulls it down, but the liquid exerts an opposite force This is called the buoyant force The upward force that a fluid exerts on an object; opposite to the pull of gravity on an object in a fluid

When the density of the liquid is greater than the density of the object the object will float When the density of the liquid is less than the density of the object, the object will sink.

Plimsoll Line

Density: A Story of Archimedes and the Gold Crown http://www.youtube.com/watch?v=KMNwXUCXLdk