Notes

Outline

Chapter 4 Physics of Matter

Vacuum A vacuum exists in outer space. It is the absence of all matter. Vacuums are relative Even in outer space some matter exists But the amount is so small that a person would die if exposed to vacuum without a space suite

States of Matter Solid Liquid Gas Plasma

Solid Solid  A rigid body, retains its shape unless distorted by a strong force..  Examples: rock, wood, plastic, iron

Liquid Flow readily, conform to the shape of their container. Have a well defined boundary (surface). More dense than gases. Examples water, beverages, blood, oil,…

Gas Flow readily, conform to the shape and size of their container, do not have a well defined surface, can be compressed or expanded readily. Examples: air, carbon dioxide, helium, steam.

Inside Liguid vs Gas

Plasma An ionized gas, often referred to as the fourth state of matter. It consists of positive ions and electrons interacts strongly with magnetic fields conducts electricity. Commonly exists only at higher temperatures or in strong electromagnetic fields Examples: Sun, candle flame, gases in operating fluorescent, neon, and vapor lights.

Structure or Particles of Matter Greeks described smallest particles of matter as atoms. Now we know there are even smaller particles. Atoms are composed of Electrons, protons and neutrons. Protons and neutrons are in the center or nucleus of the atom Electrons orbit around the nucleus

Neutrons, Protons, Electrons Neutron Electrically neutral particle residing in the nucleus of an atom. Proton Positively charged particle residing in the nucleus of an atom. Electron Negatively charged particle, usually found orbiting the nucleus of an atom.

Elements One of over 115 different fundamental substances The simplest and purest forms of matter. All have the same type of Atom, specifically the same number of protons in the nucleus. Scientists are still discovering new elements so the number is always increasing.

Examples of Elements Gold, Silver, Oxygen, Silicon, Nitrogen,…. Nitrogen is the most abundant element. It makes up about 80% of our air. Silicon is also very abundant, since it occurs in sand, a compound of Silicon and Oxygen.

Molecule/Compound Two or more atoms combine to form a molecule.  If the atoms are different types it is a compound. A Compound is something composed of identical molecules of more than one type of atom or element.  2 or more elements combine chemically. E.G. SiO2 Is a compound composed of molecules with Silicon and Oxygen atoms.

Mixture No chemical reaction, thus not a compound Parts do not combine uniformly, they just intermix. Parts can be recovered individually. Example, Instant Cocoa: chocolate, sugar, and milk powder.

Solutions A homogeneous mixture of two or more substances, which may be solids, liquids, gases, or a combination of these The parts break down into individual molecules, and intersperse, but do not combine. E.G. salt in water-salt water

Suspensions A suspension has tiny particles, but many molecules in one particle. Not a chemical reaction, thus not a compound Their particles are larger than molecules thus not a solution.

Suspensions Examples Mayonaise, Gelatin, Butter, Ice Cream Orange Juice see http://encyclopedia.thefreedictionary.com/Suspension+(chemistry)

Pressure (p) The force per unit area for a force acting perpendicular to a surface. The force acting on a surface divided by its area. P = Force/Area = F/A Force on the floor= Weight = 100 lbs Area of shoes surface 30 sq.in. Pressure on the floor =100/30= 3.33psi

Pressure from spike heels Heel area = .2x.2in=.04sq.in Sole area =2 x 4 in = 8 sq.in. Weight=100 lbs. On Heel P=100/.04 =2500 psi On Sole P=100/8 = 12.5psi.

Equal Forces Unequal P Note force is the same in both cases but the ratio of pressures is 2500/12.5 = 200 to 1!

Mass density (D) The mass per unit volume of a substance. The mass of a quantity of a substance divided by the volume it occupies. Mass density = mass/volume D=m/V = 20kg/2m3 = 10kg/m3

D of 2 x 2 x 4 m, 40KG Cube D=? M= 40 kg, Cube of dimensions 2 x 2 x 4 m.  V=lwh = 2 x 2 x 4 = 16 cubic meters D = m/V = 40Kg/ 16 m3 = 2.5 kg/ m3

Weight density (Dw) The weight per unit volume of a substance. The weight of a quantity of a substance divided by the volume it occupies. Dw = W/V = Weight/Volume = 196 N/2 cu.m =98 N/m3

Dw of 2 x 2 x 4 m, 40KG Cube Dw =? M= 40 kg, W = 40 x 9.8 = 392 N Cube of dimensions 2 x 2 x 4 m.  V=lwh = 2 x 2 x 4 = 16 cubic meters Dw = W/V = 392N/ 16 m3 = 24 N/ m3

Specific Gravity Relation between density of a material and density of water. Ratio Dx/Dw (Density of x divided by density of water).

What is the Specific Gravity of Concrete? Density of concrete =2500 kg/m3, Density of water = 1000 kg/m3. Specific Gravity of concrete = Dx/Dw = 2500/1000 = 2.5. Note, no units on sp.gr!

Pressure in Fluids Pressure increases with depth! Law of fluid pressure The (gauge) pressure at any depth in a fluid at rest equals the weight of the fluid in a column extending from that depth to the top of the fluid divided by the cross-sectional area of the column.

Law of fluid pressure The (gauge) pressure at any depth in a fluid at rest equals the weight of the fluid in a column extending from that depth to the top of the fluid divided by the cross-sectional area of the column.

Pressure in Water Water weighs 62.5 lbs/cu.ft A cube 1 x 1 x 1 ft has a surface of 1 sq.ft. At a depth of 1 ft you have 62.5 lbs/sqft pressure Multiply depth in ft by 62.5 to find P 20 ft, P = 20 x 62.5 = 1250 lbs/sq.ft.

Converting to lbs/sq.in Gauges usually use lbs/sq.in 1 sq.ft = 12in x 12 in = 144 sq.in. 62.4 lbs/sq.ft = 62.4/144 = .433 lbs/sq.in. Thus using psi:p=0.433 psi/ft x h(ft) At 20 ft. P = .433 x 20 = 8.66 psi.

Gauge pressure vs total p measures difference between inside and outside pressure? see p. 141 and 142

Buoyant force The upward force exerted by a fluid on a substance partly or completely immersed in it.

Archimedes' Principle The buoyant force acting on a substance in a fluid at rest is equal to the weight of the fluid displaced by the substance.

Floating, Sinking, or Rising Buoyant force greater than weight of object, object floats. Buoyant force less than weight, object sinks. Light object released from a submarine rises, if density less than water, otherwise sinks.

Pascal's Principle Pressure applied to an enclosed fluid is transmitted undiminished to all parts of the fluid and to the walls of the container.

Problem Force from Pressure and Area Pressure = F/A then F = P x A Side of can 8 x 10 inches? Area 8 x 10 = 80 sq in., P=14.7psi F = 14.7 psi x 80 sq.in. = 1176 lbs

Mass from Density Problem Dm = M/Vol M = Dm x Vol Vol = 2m x 3m x 4m = 24 cu.m Dm = 11,340kg/cu.m M = 11,340 x 24 = 272,160 kg.

Buoyant Force Problem Swimmer’s volume = 2 ft3 Buoyant Force,BF = ? BF= Wt of water he displaces = His Vol x density of water (62.4 lbs/ft3) 2 ft3 x 62.4 lbs/ft3 = 124.8 lbs

Formulas Chapter 4 p= F/A  Pressure is Force divided by area perpendicular to the force Dm=m/V Mass density, Dm = mass, m/volume, V Dw=w/V Weight Density, Dw = weight, w/volume, V Fb= WFD Archimedes’ Principle: Buoyant Force = Weight of the fluid displaced

Special Case Equations p=Dwh=Dm x g x h Gauge Pressure, p at a depth h in a liquid of wt density Dw or mass density Dm p=0.433 (psi/ft) x h(ft) Gauge Pressure in psi underwater at a depth h in feet

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