Answer: Frictional force is when it happens on purpose and normal force is when it happens normal and you are not trying to make it happen on purpose.
Explanation: friction happens on purpose and sometimes you can't control friction but friction is an important thing.
When child swings on the swings energy transfers from potential (on the top points) to the kinetic (on the bottom).
Answer;
-A vent stack
Explanation;
-A vent stack is best described by, the vertical, upper portion above the top-most fixture through which gases and odors escape the sanitary drainage system, carrying no liquids or solids.
-The vent stack usually runs parallel with the soil/waste stack and may either extend up through the roof or connect to a stack vent. While a stack vent is the uppermost portion of a soil/waste stack that continues the pipe from above the highest connected fixture out the roof.
F = kq1q2/r²
F = 9.0(10^9)(10)(50)/20²
F = 1.125 * 10^10 N
The planet Mercury. Hope this helps