Week 4 of a 10 week course on Freshman Physics

1. Module 3 Part 1
Atomic Theory
Properties of Matter
Buoyancy
Ideal Gas Law
Dr. Paul H. Comitz
pcomitz@live.com

2. Agenda
 Matter
 Atomic Theory
 Properties of Matter
 Solids
 Liquids
 Gas
 Ideal Gas Law
 Lab : Gas Properties
 http://phet.colorado.edu/en/simulation/balloons-
and-buoyancy

3. Course Modules
# Module Weeks Reading Quiz
1 Newton's laws 1 Ch 4,5 *
2 Conservation of Energy and
Momentum
2,3 Ch 6,7,8 Quiz 1
3 Thermodynamics 4,5 Ch 12,13,14
4 Electromagnetism 6,7 Ch 17,18 Quiz 2
5 Waves, Sound, and Light 8,9 Ch 16, 20, 21 Quiz 3
6 Modern Physics 10 Ch 23 Final Exam
* it is strongly recommended you read chapters 0 - 3

4. Module 3
 Reading: Chapters 12,13,14
 Chapter 12 – Matter
 Chapter 13 - Fluids
 Chapter 14 – Temperature and Heat Transfer
 The Physics Classroom
 http://www.physicsclassroom.com/class/thermalP
 Exercise , due start of week 6 (4%)
 Discussion – due next week (5%)
 Labs
 Gas Properties (3.75%)
 Temperature and Heat (3.75%)

5. In Class Discussion
Pascal’s Principle (text 13.2)
 Pascal’s principle states that a change in pressure in one part of a fluid is
transmitted to every other part; this is also the principle behind hydraulics.
Hydraulic devices can be used to multiply an applied force with the trade-off of
having to apply the force over a greater distance. Hydraulic devices are
commonly found in many areas of everyday life.
 In this discussion, you need to:
 Research and identify a device that uses hydraulics to operate. Use the ITT Tech
Virtual Library and other resources for your research.
 In your own words, describe the device and the method to apply Pascal’s principle to it.
Use two examples to illustrate your explanation.
 Include references to all sources you used in your research and posting.
 Requirements:
 Provide a complete, well-thought-out response.
 Approx. 1 page (200 to 250 words)
 Bring your completed work to next class
 Be prepared to briefly present your response to the class

6. Atoms in Motion
Richard P. Feynman , Lectures in Physics, Chapter 1 , Atoms in Motion
all things are made of atoms—little particles that move around in
perpetual motion, attracting each other when
they are a little distance apart, but repelling upon being squeezed into
one another.

7. Atomic Hypothesis
 Ancient Greece Aristotle
 384 – 322 BC
 All things are composed of
 Earth, Air, Fire, Water
 5th Century Greece
 All things are made of atoms
 1827 Robert Brown
 The perpetual and haphazard jiggling of atoms
 Brownian motion

8. Properties of Atoms
 Too small for us to see
 Electron orbit radius
 5.291 x 10-11 m
 Always in motion
 Absolute Zero , most motion in
an atom stops
 0 K, -273 C, -454 F
 Ageless
Bohr Model

9. Bohr Model of the Atom*
 Classical Model
 Atom is a small particle
 Positively charged nucleus at
center
 Nucleus is made up of
protons and neutrons
 Protons positive charge
 Neutrons no charge
 Negatively Charged Electrons orbit
nucleus
 Mass of electron is much, much smaller
than mass of protons and neutrons
Helium by Svdmolen/Jeanot (converted by King of Hearts) - Image:Atom.png, CC BY-SA 3.0,
https://commons.wikimedia.org/w/index.php?curid=1805226
* Note that this is a model. In modern physics there are alternate models

10. Elements are made up of Atoms
 Element
 a material that is composed of a single type of
atom
 In 2016 there are 118 known elements
 Most naturally occurring, some synthesized
 Approximately 90+ elements occur natural
 Others synthesized
 Periodic Table lists all elements
 Living things
 Hydrogen, Oxygen, Carbon, Nitrogen, Calcium

11. Periodic Table

12. Periodic Table
Note – scale shown in helium and hydrogen are not relative
Atomic Number – number of protons in the nucleus

13. Compounds and Molecules
 A molecule consists of two or more atoms
bound together
 A compound contains more than one element
 Pulling molecules apart requires energy
 Combining molecules releases energy

14. Matter
 Matter is composed of atoms
 Matter exists in multiple states
 Solid
 Molecules are close together at fixed
distance
 Vibration back and forth
 Liquid
 Molecules further apart, not fixed
 Molecules flow over one another
 Definite Volume
 Gas
 Molecules move rapidly in all directions
 Compressible
 Same volume as container

15. States of Matter

16. Properties of Matter
Stress
 Stress is the ratio of applied force over the
area over which that force acts
 S = F/A
 F/A is referred to as Pressure and given the name
Pascal
 1 N/m2 = 1 Pa
 A brick laying on a table weighs 12N and has
area of 8 cm x 16cm. What is the stress on
the table?
 S = 12N/128 cm2 = 938 Pa
 Don’t forget 100 cm = 1m

17. Properties of Matter
Hooke’s Law
 The ratio of the force applied to an object to its change in
length (resulting in its being stretched or compressed by
the applied force) is constant as long as the elastic limit
has not been exceeded
 The elastic limit of a solid is the point beyond which a deformed
object cannot return to its original
 F/Dl = k
 F = applied force
 Dl = change in length
 k = elastic constant

18. Hooke’s Law Example
 A force of 3.00 lb stretches a spring 12.0 in.
What force is required to stretch the spring
15.0 in.?
 Find k : Use F/Dl = k
 F1 = 3 lb
 Dl = 12 in
 k = 3lb/12 in = 0.25 lb/in
 Find F2
 F2 = k/ Dl = (0.25 lb/in) (15in ) = 3.75 lb

19. Density
Mass Density and Weight Density
 Mass Density
 A measure of mass per unit volume
 Symbol r (Greek letter rho,
pronounced row)
 Mass Density = m/V
 m is mass m, V is volume
 Weight Density is
 Weight per unit volume
 Weight Density = Fw/V
 Fw is weight V is volume

20. What is the difference between Weight
and Mass ?
 Mass – measure of how much matter an
object has
 Weight - measure of how hard gravity is
pulling on that object

21. BUOYANCY AND
ARCHIMEDES’ PRINCIPLE
THE IDEAL GAS LAW

22. Buoyancy
Archimedes’ Principle
 Any object placed in a fluid apparently loses
weight equal to the weight of the displaced fluid
 Applies to gases and liquids
A completely submerged object always displaces a
volume of liquid equal to its own volume.
example: Place a stone in a container that is
brim-full of water, and the amount of water
overflow equals the volume of the stone
weight of stone = weight of displaced water

23. The Buoyant Force
 Net upward force that a fluid exerts on an
immersed object = weight of fluid
displaced
 Why does a balloon float?

24. Ideal Gas Law
 Watch the following video
 https://www.khanacademy.org/science/chemistry/
gases-and-kinetic-molecular-theory/ideal-gas-
laws/v/ideal-gas-equation-pv-nrt
 pV = nRT
 p = Pressure
 V = Volume
 n = particles in gas
 R = proportionality Constant
 T = temperature in Kelvins
 Pressure and Volume proportional to
Temperature

25. In Our Lab
 Alternate form of Ideal Gas Law
 pV = kBNT
 P = pressure in Pascal N/m2
 V = volume = m3
 N number of gas molecules in V
 kB = 1.38 x 10-23 J/K
 T = temperature in Kelvins
 0K = -2730 C = -4540 F
 Be careful with dimensional analysis
 109 nm = 1 m