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