Technological advances clearly.
Theories change due to other peoples view on the matter and how they experiment with it, but Technology advancements are the greatest factor of all. I mean seriously, we wouldn't know of cells before the microscope and when they first invented it, it advanced further and now we can see things on a whole deeper lever.
Fast Communication, can be used for good and can be used for bad hackers.
Answer:
F=m*g is the formula and the answer is 19,620 kg
Explanation:
Since the formula is F=m*g and Earth's gravity is 9.81 m/s^2 all you need to do is multiply 2,000 by 9.81
Answer:

Explanation:
For this case we have the following info given:
Number of Na+ ions 
Each ion have a charge of +e and the crage of the electron is 
The time is given
if we convert this into seconds we got:

Now we can use the following formula given from the current passing thourhg a meter of nerve axon given by:

Where N represent the number of ions, e the charge of the electron and Q the total charge
If we replace on this case we have this:

And from the general definition of current we know that:

And since we know the total charge Q and the time we can replace:

The current during the inflow charge in the meter axon for this case is 
You measure the total distance the bike travels, and the total time it takes to travel that distance. You then divide the distance by the time