PHASES OF MATTER• There are 3 basic phases of matter: solid, liquid, gas (plasma).• Plasma is a gas that contains ions and conduct electricity. 99% of the universe (the stars) is comprised of plasma. Plasma is sometimes called the 4th state of matter.

While different phases have different particle arrangements, the atomic motion never stops!

What changes from phase to phase is the amount of atomic motion and the bonds between the atoms.

Phase Motion Bonds

Solid Vibrations Fixed

Liquid Free Motion Bonded, but free

Gas Free Motion Not bonded!

No matter what the phase, the molecular motion never stops. It is described by:

The Kinetic Theory of Matter

1) The molecules of a substance are in constant motion.

2) Collisions between molecules are perfectly elastic.

Forces between molecules:

• in a gas, the molecules separate spontaneously, making particles basically independent of each other.

• in liquids and solids, the particles are bonded and so they attract when pulled apart. They will then repel when too close.

THE SOLID PHASE• Solids have a definite shape and a definite volume.• The particles of a solid are bonded in a “fixed” position- they only vibrate!

• A crystalline solid has a regular arrangement (and so a set melting point). Ice, sugar, iron.

• An amorphous solid has a random particle arrangement (and so an unfixed melting point). Wax, butter.

Properties of Solids (and sometimes fluids):

• Diffusion-- the penetration of one particle into a second type.• Cohesion-- force of attraction between same kind of molecules• Adhesion-- force of attraction between different kinds of molecules.• Ductility-- ability of a solid to be pulled into a wire.

• Malleability-- ability of a solid to be hammered into a sheet

• Elasticity-- ability to return to original shape when distorting forces are removed.

• Elastic Limit-- the point at which the object will not return to its original shape

Stress-- the ratio of force per cross-sectional area of a stretched object.

stress =F

A

units:

N

m2

Stress produces strain-- the relative amount of deformation (stretch) produced. It is the ratio of the change in length to the original length:

strain = ∆l

l

there are no units for strain!

Hooke’s Law: within the elastic limit of an object, the ratio of stress to strain for a given material will remain constant.

The numerical constant that reflects the elasticity of a material is called the Young’s (or Elastic) Modulus (E).

E = stress

strain

= F/A

∆l /lE =

F l

A∆l

the units would be N/m2, since strain has no units!

The ratio of breaking force to cross-sectional area is another useful property. This is called the Tensile Strength (or Ultimate Strength) of the material.

U =Fbreak

Aunits: N/m2

Material E (N/m2) U (N/m2)

Iron 100 X 109 170 X 106

Steel 200 X 109 500 X 106

Copper 120 X 109 230 X 106

Aluminum 70 X 109 200 X 106

Bone 15 X 109 130 X 106

A piece of 25 gauge (A=.162mm2) copper wire is 43.00 cm long when 325 N are hung from it. What is the new length of the wire?

A = .162 mm2

l = 43.00 cmF = 325 N

E = 11.6 X 1010 N/m2

l = ?

(1 m2/10002 mm2) = 1.62 X 10-7 m2

∆l = F • l

A•E = (325 N)(43.0 cm)

(1.62 X 10-7 m2)(11.6 X 1010 N/m2)

= .744 cm

l = l + ∆l = 43.00 cm + .744 cm = 43.74 cmHow much force is needed to pull apart a piece of

32 gauge (A=.0320 mm2) aluminum wire?

Fbreak = ?

A = .0320 mm2

U = 2.4 X 108 N/m2

(1m2/10002 mm2) = 3.20 X 10-8 m2

Fbreak= U•A

= (2.4 X 108 N/m2)(3.20 X 10-8 m2)

= 7.68 N

A piece of silver wire that is originally 1.0000 m long is stretched to 1.0043 m when 555 N is suspended from it. What must be the cross-sectional area of this wire?

E = 7.75 X 1010 N/m2

l = 1.0000 m

∆l = l - l = .0043 m

F = 555 N

A = ?

A = Fl

E∆l

= (555 N)(1.0000 m)

(7.75 X 1010 N/m2)(.0043 m)

= 1.66 X 10-6 m2 (10002 mm2/1 m2)

= 1.66 mm2

A force of 31.7 N is used to pull apart a piece of 25 gauge wire. What material must the wire be made of?

Fbreak = 31.7 N

A = .162 mm2

U = ?

(1 m2/10002 mm2) = 1.62 X 10-7m2

U = Fbreak

A

= 31.7 N

1.62 X 10-7m2

= 1.96 X 108 N/m2

Aluminum

1 ) A vertical steel (E = 200 X 109 N/m2) rod of cross sectional area .15 m2 has a 2000.0 kg sign hanging from it. A) What is the stress in the girder? B)What is the strain on the girder? C) If the girder was 9.5000 m long before the sign was hung, how much will it stretch with the sign on it?2) A force of 188.4 N is used to pull apart a 24 gauge (A= .205 mm2) wire. What must the tensile strength of the wire?

3) A nylon (E= 5 X 109 N/m2) tennis string on a racket is under a tension of 250 N. If its diameter is 1.00 mm, by how much is it stretched if the original length of the wire was 30.0 cm?

4) How much weight needs to be hung from a brass (TS = 80 X 109 N/m2) wire with a cross sectional area of .320 mm2 in order to break the wire?5) A 15.0 cm long animal tendon stretches .37 cm by a force of 13.4 N. The tendon has a diameter of .85 cm. What must be the Elastic Modulus of this tendon?6) A 43.0 cm piano wire is stretched 2.35 X 10-3 m by a force of 710.0 N. The wire has a radius of 0.454 mm. What is the Young’s Modulus of the wire?