# Chapter 17 Notes.

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Chapter 17 Notes

Overview of Chapter 17

Properties of Solids Density- describes the relationship b/t mass and volume of homogenous material- tells how tightly molecules are “packed” Formula: D=m/v What are the units of density? Density stays the same no matter how large or small the sample is Heterogenous materials may not have the same density throughout

Ideas from lab 17.1 Density does not depend on size of the material
Density does depend on the type of material Density does not depend on the shape of the material (unless you have altered volume) Density does depend on the state of matter

Other properties Hardness-resistance to scratching
Elasticity-ability to stretch then return to original shape Brittleness-tendency to shatter on impact Malleability- ability to be pounded into sheets Tensile strength- measures how much tension a material can withstand without breaking

Density of Fluids Fluid- matter with the ability to flow (applies to gases too) The liquid form of a material is usually less dense than the solid form of a material- Why? As temperature increases, the density decreases- Why? The exception: solid water is less dense then liquid water- Why?

Ideas from lab 17.2 Layering is a qualitative method of comparing densities of different fluids The most dense fluid will be at the bottom, the least dense fluid will be at the top. Some real-life uses for layering: oil refineries, steel blast furnance

Buoyancy The measure of the upward force a fluid exerts on an object
Archimedes principle- the force exerted on the object is = to the weight of fluid displaced by the object

Getting objects to float- Points from lab 17.3
To get an object to float, you need buoyant force to equal the force of the object In other words, the weight of the displaced water needs to equal the weight of the object How could you increase the amount of displaced water? Change the shape of the substance so the surface area is increased and will displace more water This also changes its density by increasing the object’s volume while the mass remains unchanged.

Viscosity Definition: material’s resistance to flow
What determines viscosity? The ease at which molecules can move past one another This depends on: the size and shape of the molecule how tightly packed the molecules are

Temperature and viscosity
As temp increases liquids usually become less viscous because molecules are spread out more and molecules have an easier time moving past one another Gases become MORE viscous with increasing temperature- this is because as molecules move around more, they will collide more creating more friction and greater resistance to flow

Compressibility of gases
Since molecules in a gas are far apart, they can be compressed to decrease its volume. Adding pressure will compress gases, leaving empty space were the gas molecules used to occupy Once the pressure is released, then the gas will expand, filling the empty space

Cartesian divers If pressure is applied to the system, the gas inside the diver compresses This compression allows space for water to enter This added water increases the density, then the diver sinks What causes it to float again?