The South Street Effect

In South Philadelphia, there is a street on which you can find nearly anything, from hats to lettuce to offensive t-shirts to used copies of children's books to fine dining to dive bars. You can also find people of all types, from older folks strolling along, to young married couples with small children, to college kids, to high schoolers trying to be college kids, and from straight-laced conservatives to wild hippies to goths to street people.

Every city has a "South Street." It is not the name of the street that matters, you may imagine any street that you prefer, but for the sake of this text we will discuss South Street.

Now imagine that you are walking down South Street and you see someone “very fine” coming the other way. (I'll leave it up to your imagination to decide what “very fine” means.) As they pass, you might look away shyly or try to make eye contact. You might subtly (or even not so subtly) turn to watch them walk on in the other direction. What matters is that in some way your movement will be affected.

Now imagine that on a different day you are driving through your neighborhood on a busy street and the same “'very fine” individual passes you, driving the other way. You might quickly glance around but the effect on your motion will be much less.

Now imagine that you are on the highway and once again pass that “very fine” individual. You might not even have a chance to react.

The difference in these cases is NOT the strength of the attraction. After all, you haven't changed, nor has that “very fine” individual. What has changed is TIME. The faster you are going, the less time there is to react to that attraction. The same is true of molecules.

The faster two molecules pass by each other (or even collide with each other) the less time they spend near each other and the less effective the attraction between them will be.

Remember that temperature is a measure of the average speed of the molecules in a sample. So that as the temperature increases, the molecules move faster, as a result the attractions holding them together become less effective (not weaker). This is what we will call the South Street Effect.