Physical barriers are often due to the nature of the environment.
There had been no barriers between them, physical or mental.
After the 1967 war, all the physical barriers were torn down.
When factors change, especially physical barriers, often, species will branch off.
The presence of a physical barrier also acted as a legal one.
These may be physical barriers, such as living far from your doctor or pharmacy.
Physical barriers to gene flow are usually, but not always, natural.
These include physical barriers, which make the effort of stealing the vehicle more difficult.
Hasn't technology made the physical barrier obsolete to border security?
In both cases, treatment provides a physical barrier to flame spread.