While someone is skateboarding, the wheels of the skateboard are in contact with the ground. The skateboarder _[blank 1]_ on the ground to move the skateboard forward, but if the skateboarder doesn’t, _[blank 2]_ causes the skateboard to slow down and eventually stop.

On a mild saturday morning while people are working inside, the furnace keeps the temperature inside the building at 23degreesc. at noon the furnace is turned off, and the people go home. the temperature outside is a constant 16degreesc for the rest of the afternoon. if the time constant for the building is 3 hr, when will the temperature inside the building reach 18degreesc? if some windows are left open and the time constant drops to 2 hr, when will the temperature inside reach 18degreesc?