A heater is placed under one corner of a water bed mattress

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.

There is a single path for electrons. the current decreases when additional resistors are added. the current will be the same in each resistor. these statements best describe a(n) circuit.

Electromagnets coils of wire paper clips picked up 10 3 15 6 20 9 25 12 ms. owens' class was studying magnets. ms. owens showed her students how to make an electromagnet using a nail, a d-cell battery, and plastic coated wire. the students wrapped the wire around the nail and then attached the ends to the battery. when they were finished, they tested their magnets by investigating how many paperclips their magnets could pick up. they also tested whether they could increase the strength of their electromagnets by using more coils of wire. they recorded the class average of their results in the data table seen here. ms. owens asked her students to graph their data in a line graph. how should the students label the x-axis on their line graph? a) size of battery b) number of paper clips c) number of coils of wire d) strength of electromagnet