Maxwell speed distribution
At a given temperature some molecules are fast and some slow, yet together they follow a stable statistical law.
Gas molecules collide constantly and their individual speeds vary enormously, yet the speed distribution of a large number of molecules is well defined: very slow and very fast molecules are both rare, and intermediate speeds are the most common. When the temperature rises or the molecular mass decreases, the peak of the curve shifts toward higher speeds and becomes flatter, while the total area under the curve always remains 1. The three characteristic speeds satisfy vp < v̄ < vrms.
Speed distribution of nitrogen N₂
Green is the 300 K reference; the higher the temperature, the further right and lower the peak.
Think about it
When the temperature rises from 300 K to 1200 K, by what factor does the most probable speed change?
By a factor of 2. vp = √(2kT/m) ∝ √T: the temperature increases 4 times, so the speed increases 2 times. At the same time the peak height halves, because the area under the curve stays equal to 1.
Model assumptionsIdeal gas in equilibrium · the speeds of the 48 molecules on screen are taken at evenly spaced quantiles of the distribution · collisions between molecules are not shown; molecules bounce off the walls
Data log
Set the parameters and click “Record data”. Record several rows with different parameters to plot their relationship and fit a straight line; pause and record at different times to study how a reading changes with time.