During space flight, astronauts often refer to forces as multiples of the force of gravity on Earth's surface. What does a force of 5g mean to an astronaut?

Question

During space flight, astronauts often refer to forces as multiples of the force of gravity on Earth's surface. What does a force of 5g mean to an astronaut? 
If Earth were twice as massive but remained the same size, what would happen to the value of g?

http://hyperphysics.phy-astr.gsu.edu/Hbase/forces/isq.html

http://en.wikipedia.org/wiki/Acceleration_due_to_gravity