ocr: ASCENT AND DESCENT ASCENT DESCENT The burner heats UIP When the burner the air in the UPTHRUST cuts out, the air in envelope to about the envelope cools. 212°F (100°C).The As it contracts, more air expands, pushing air enters the base cold air out of the oft the envelope. base of the balloon. This extra air The balloon's increases the weight overall weighti is BURNER. ofthe balloon sO reduced to less than that it exceeds the the upthrust, and upthrust, making the balloon rises. Down the balloon descend. - WEIGHT
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