Answer:
horizontal structural member that supports a floor. Beams are typically wood, cold formed metal framing or steel.
Joists
Horizontal timbers, beams or bars supporting a floor.
Answer:
F_n = 5.65E-11 N
d = 1.20682E-31 m
Explanation:
F = 3.8E-09 N
where
m = Mass of electron = 9.109E−31 kilograms
G = Gravitational constant = 6.67E-11 m³/kgs²
x = Distance between them

For 

Dividing the above equations we get

F_n = 5.65E-11 N

d = 1.20682E-31 m
Batteries supply electrons to the circuit by releasing negatively charged atoms or ions. These ions are produced by the batteries through a chemical reaction that spontaneously occurs within the battery. So the negative end of the battery pushes the ions towards the positive end of the circuit with the help of the voltage. This is why eventually, batteries "run out" when the electrode is used up and the chemical reaction can no longer continue.
The lens changes the focal distance of the eye so that you can focus on images/objects.