A hot air balloon is open at the bottom and the passengers in the basket beneath can see the inside of the balloon's envelope or "skin." Hot air doesn't flow out of the balloon's open bottom because
A. viscous forces slow the flow of air out of the balloon.
B. the balloon's canvas envelope pulls outward, sucking air into the balloon.
C. the air inside that open bottom is at atmospheric pressure.
D. the flame pushes the air up into the balloon through that open bottom.
Answer:C
A hot air balloon is open at the bottom and the passengers in the basket beneath can see the inside of the balloon's envelope or "skin." Hot air doesn't flow out of the balloon's open bottom because
A. viscous forces slow the flow of air out of the balloon. B. the balloon's canvas envelope pulls outward, sucking air into the balloon. C. the air inside that open bottom is at atmospheric pressure. D. the flame pushes the air up into the balloon through that open bottom.