A Physical Constraint is a type of Constraint that be influenced by either internal or external sources. These constraints are physical, tangible, and measurable in terms of size, speed, geography, etc. Generally, you will have some control over an internal physical constraint and have no control over an external physical constraint.
Below are examples of physical constraints that may be internal or external:
Time (hours in a day, time of year / seasonality, working hours, speed)
Staffing availability
Size, physical design, or measurement limitations
Weight limitations
Technology requirement (e.g., from the customer)
Resource availability (e.g., water, electricity, land)
Demographics
Geography restrictions
Capacity (e.g., throughput, power)
Hints:
Physical Constraints can be either Internal or External Constraints. An external Physical Constraint is something that the business COULD control, such as the number of shifts the business runs or if workers are allowed to work overtime. On the other hand, an internal Physical Constraint could be the fact that there are only 24 hours in a day, that the customer location is in another state, etc.
If your customer demands the use of a certain technology to deliver results but your management does not, this is an example of an external Physical Constraint (not an internal).