Question about isothermal work why heat is not affected

[MK300]

What I think I understand so far:
Internal energy is the sum of work done on a system and heat supplied to the system.
In an isothermal case there is no change in temperature therefor internal energy has no change. therefor -q=w

Question: Why is there heat? I thought heat is the energy flow formed from temperature differences. I'm confused as to what heat is and why it is not effect in an isothermal case.

Background: first semester in physical chemistry

[Andy Resnick]

If I understand your question, you are asking how work is converted into heat: Joule's experiment. His experiment showed that work energy can be converted into heat energy. The specific mechanism in Joule's experiment is viscosity-viscosity acts to dissipate energy.

[MK300]

Ok I think I understand. My problem was: how can there be heat if there is no temperature difference, and your answer is that it is evolved from work.
Sorry I'll stop after this question.
Where is the heat coming from when work is done?
What happens is the microscopic level when work is done. Does the molecule run out of its ability to do work and then the remaining property is converted to heat? Or is heat evolved because the molecules are moving which releases heat? I heard when electrons move they generate a magnetic field, so maybe when atoms move they generate heat?

[Andy Resnick]

Work is transformed into heat via friction/viscosity (dissipative processes). We do not yet have a microscopic model of dissipative processes- we are currently unable to 'explain' friction or viscosity in terms of the 4 basic forces (gravity, e&m, strong, weak) because those forces are conservative forces- 'lossless', if you like.

[MK300]

Thanks Resnick for your time and quick replies. I enjoy learning about physical chemistry and hopefully later I will contribute back to this forum.