Astronomers send probes to other planets to take pictures of their surfaces. An astronomer thinks that briny water flows on Mars because he noticed certain features in one picture of Mars. Which method did the astronomer use to form this hypothesis?
1.reading scientific literature
2.making careful observations
3. analyzing a natural experiment
4. conducting a controlled experiment

Hot air balloons float in the air because of the difference in density between cold and hot air. in this problem, you will estimate the minimum temperature the gas inside the balloon needs to be, for it to take off. to do this, use the following variables and make these assumptions: the combined weight of the pilot basket together with that of the balloon fabric and other equipment is w. the volume of the hot air inside the balloon when it is inflated is v. the absolute temperature of the hot air at the bottom of the balloon is th (where th> tc). the absolute temperature of the cold air outside the balloon is tc and its density is ďc. the balloon is open at the bottom, so that the pressure inside and outside the balloon is the same. as always, treat air as an ideal gas. use g for the magnitude of the acceleration due to gravity.

Which part of a feedback mechanism is able to monitor the conditions outside of cells and usually uses nerve cells to relay this information to an intergrating center

Compare and contrast physical changes with chemical changes.