Look at the rock sitting on the hill in the picture above. gravity should make the rock slide down the hill. what force is acting to balance gravity, keeping the rock in place?
a. centripetal force
b. gravity
c. momentum
d. friction

Look at the rock sitting on the hill in the picture above. Gravity should make the rock slide down the hill. What force is acting to balance gravity,keeping the rock in place? - D. friction
Centripetal force and momentum have to do with movement. Gravity cannot balance gravity. 

Julia would be observing a. static electricity was caused by her sweater rubbing against her shirt and transferring electrons. she didn't touch anything metal, so that would cancel out b.she most likely didn't rub her sweater against her hair either, so that cancels out c.she also didn't scoot across the carpet while trying to take her sweater off, that cancels out d.so that leaves a.a. is correct.