because some countries are higher than others
If you are EU citizen from one country to another EU country, you pay tax, which vary from one EU country to another.
Yes it is legal to live in one country and work in another. The rules and requirements for doing so vary for each country.
Different air pressure, so there is more/less air resistance.
Yes, particles in the nebula attracted to one another by gravity?
It depends on the taxes, which vary from one country to another.
The answer will vary from one country to another.
The answer will vary from one country to another. An international percentage would not be based on consistent definitions.
The answer will vary from one country to another. You have not specified which country (or region) and so the question cannot be answered.
Gravity
Gravity.
One such force is gravity; basically, gravity is the ONLY force that affects ALL objects.
There is no standard size for a classroom - they vary from school to school, from city to city, and from one country to another.