What would be an ideal experiment to test how different types of surfaces affect friction?
a)two objects of equal weight placed on two glass surfaces of equal lengths
b)two objects of equal weight placed on two glass surfaces of unequal lengths
c)two objects of equal weights placed on a glass surface and wooden surface
d)two objects of different weights placed on two wooden surfaces of unequal lengths

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.

What is a metal replacement reaction

George is a dalmatian puppy. describe what happens to light that allows you to see george’s black and white coat.