Activity B:
Average particle
velocity
Get the Gizmo ready:
Select Hydrogen gas.
Set the Temperature to 300 K.
Introduction: The graph on the right side of the Gizmo represents the Maxwell-Boltzmann
distribution of particle velocities. The curve represents the probability of a particle moving at
the velocity shown on the x-axis of the graph. The higher the curve, the greater the probability of
finding a particle moving at that velocity will be.
Question: How are particle velocities distributed?
1. Observe: Move the Temperature slider back and forth. This time focus on the graph at right.
What do you notice about the shape of the graph? _________________________________
_________________________________________________________________________
_________________________________________________________________________
_________________________________________________________________________
2. Analyze: Look at the left side of the graph as you raise the temperature from 50 to 1,000 K.
A. Even at the highest temperatures, are there still a few slow particles? ____________
B. At what temperature do you see the widest variety of particle velocities? __________
C. In general, is the Maxwell-Boltzmann curve a symmetrical or an asymmetrical curve?
___________________________________________________________________
3. Estimate: Because particles have a range of velocities at any given temperature, it is useful
to calculate the average velocity. Physicists express the average velocity in three ways:
most probable velocity (v
p
), mean velocity ( ), and root mean square velocity (v
rms
).
Set the temperature to 200 K (the selected gas should still be Hydrogen).
A. Estimate the most probable velocity by looking at the peak of the curve. What is your
estimate? ______________
B. Turn on Show most probable velocity. What is the actual value? ______________
C. Base on the shape of the curve, do you think most of the particles are moving faster
or slower than the most probable velocity? ______________
(Activity B continued on next page)
When the temperature is low and colder the graph has a high peak and doesn't
stretch out in length very much. When the temperature is high and hotter the graph
has a low stretched line that exceed very high.
faster but somewhat
slowly at the same time