SelfPaced Physics Cover Sheet
Activity 2 - Atoms
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PHYS 1000
Activity: Atoms
Objective
The student should understand (a) how atmospheric atoms diffuse from a
source, and (b) a basic relationship between pressure and temperature of gases.
Background
(Reference: Chapter 2, Physics, Concepts and Connections, Art Hobson)
Atoms in the atmosphere are moving at great speed, continually bouncing off of
each other and off of surfaces. Imagine the smell of cookies baking in an oven. You can
smell those cookies because atoms from the dough have traveled into the air, through
the room, and into your nose, in a process called diffusion. The path that molecules
take can be modeled as a random walk (Figure 1.)
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The faster that the molecules are moving, the harder they will strike a containing surface
such as a wall. The net amount of force per area on a surface is the atmospheric
pressure.
Equipment and Supplies
Diffusion experiment: 5 coins (four pennies and a nickel for flipping)
Temperature: a round balloon, freezer, boiling pot of water, ruler, two large hardcover
books
Procedure part 1: Diffusion
Take four coins and place them on the center tile. Take a fifth coin and flip it. If the
flipped coin reads heads, move one of your four coins one square to the right (+1.) If it is
tails, move it left. Do the same for the other three coins. Do this again for all four coins.
Some of the coins might move back to the center square. Repeat this procedure until a
coin lands on an outer square: either Joe’s nose or your nose. Keep track of how
many steps it takes a coin to reach one of the endpoints. Repeat this experiment
five times and record your results.
Joe
-4 -3 -2 -1 0 +1 +2 +3 +4
You
Procedure part 2: Relationship Between Temperature and the Speed of
Atmospheric Molecules
Blow up a balloon and tie off its end. Measure its diameter by placing it between
two books, and measuring the distance between the books. Put the balloon in the
freezer for 5 minutes. Quickly remove it and measure its diameter again. Hold it over
boiling water for a minute or so, and quickly measure its diameter again.
Worksheet
Questions
1) Do the coins diffuse outward from the center?
2) For the five trials, how many times was (a) Joe’s nose reached first, (b) your
nose reached first, and (c) Joe’s and your nose reached at the same time?
3) For each trial, how many sets of coin flips did it take for a coin to reach either
nose?
Trial 1)______ Trial 2) ______ Trial 3) ______ Trial 4) ______ Trial 5) ______
Average number of coin flips (out of the five trials) ___________
4) Set up a new game where it is 10 squares to either nose (instead of 5). Record
how many sets of coin flips did it take for a coin to reach either nose.
Trial 1)______ Trial 2) ______ Trial 3) ______ Trial 4) ______ Trial 5) ______
Average number of coin flips (out of the five trials) ___________
Did the average number of coin flips double (since the distance to either nose
doubled)? Discuss your result.
5) Do you think if you had only one coin, this experiment would take more steps on
average, or fewer steps? What if you had 100 coins?
6) What are the similarities between this process and the process of physical
diffusion of an odor as discussed in the chapter?
7) Initial diameter of balloon______________
Diameter of cold balloon ______________
Diameter of hot balloon _______________
8) Explain why the balloon shrinks and contracts with temperature.
9) The basic relation between the velocity v and the temperature T is:
! mv2 = 3/2 kBT
where m is the mass of the atom and kB is the Boltzmann constant
kB =1.38 x 10-23 Joule/Kelvin (J/K).
(1)
Most of the atoms you breathe are made of diatomic nitrogen N2, which has a mass of
2.32 x 10-26 kg. If room temperature is about 295 K, how fast is a typical air molecule
moving in units of m/s? HINT: solving equation (1) for v gives:
v=
3k B T
m
Answer: v = _______________________m/s.