Why is reentry so hot?

Related questions

1. Why is absolute zero impossible to reach?
2. What's the temperature in Antarctica right now?
3. Is Alaska colder than Antarctica?
4. Is Arizona hotter than California?
5. Is 0 possible?
6. Is it ever hot in Siberia?
7. Is it always cold in Siberia?
8. Is Florida or Arizona hotter?
9. Is Russia same as Siberia?
10. What is the coldest habitable place on Earth?

Tags

1. #shock
2. #layer
3. #heating
4. #caused
5. #isentropic
6. #friction
7. #direct
8. #reentry
9. #within
10. #entropy
11. #increases
12. #cause
13. #molecules
14. #mainly
15. #object
16. #account
17. #based
18. #compression