Describe two ways to change the frictional force between two solid surfaces.

-- To increase the frictional force between the two surfaces, press them together
harder, or rough up the area of contact with sandpaper or dirt.

-- To decrease the frictional force between two surfaces, decrease the force
with which they press together, or smooth (polish) the area where their surfaces
contact, or make the area seem smoother by lubricating it with grease, oil, air,
or smooth leaves.

Humid continental climate is found in the interior of continents between the 30 and 60 degrees latitude, but usually above the 40 degree line.   40 degrees north of the equator means less direct sunlight and therefore less warmth.   this climate is mainly found in the northern hemisphere since there are no major landmasses in the southern hemisphere.  if you live in northern indiana, you know all about humid continental because that is the climate type you have!

So  if  the sum of the enthalpies of the reactants is greater than the products, the  reaction  will be  exothermic.  if  the products side has a larger enthalpy, the  reaction  is  endothermic. you may wonder why  endothermic reactions, which soak up energy or enthalpy from the environment, even happen