If every person in china faced exactly the same direction and took a
step at exactly the same time would it make a change to the earths
rotational speed and/or orbit

It would depend on the direction, the size and the heaviness of their step.

The Chinese are noted for their lightness of foot and so they could be
relied upon not to disturb the Earth's equilibrium.

Please don't ask about the people in the United States.

Hi Hoges,

Probonopublico beat me to it. Anyway .. the answer is NO.

Stepping is simply a transfer of weight distribution.
The causality of Earth's revolutions are not dependant upon human footsteps.
Should the entire population of Earth attempt an experiment of
residing on the island of say Zanzibar, then your weight distribution
test may have some credence. The forecast calculation of impact upon
the Earth would be arguable. At least the remainder of the Earth may
silently express a sigh of relief as we anihalate one another upon
Zanzibar.

Then again, if the Chinese chose to step in the right direction, I'm
sure that we would find a positive outcome for all.

On the other hand, if the physical steps taken were vertical, of
sufficient height and suspended for a duration, the landing area may
differ from the take-off point. Gravity does not begin from the
Earth's surface, it is well above head height of the average Chinese.

Phil

The rotational speed would change by a very small amount.  Let's say
there are a billion Chinese people (there might be a few more), and
that they weigh 100 kg each (this is an overestimate, but I do hear
that obesity is a growing problem in China).  They all begin to walk
east at the relaxed pace of 1 m/s.  Ignoring silly factors like the
cosine of the latitude and taking the earth's radius as 6 million
meters, they represent a change in angular momentum about the earth's
axis of about 6e17 kgm^2/s.  Approximating the earth as a homogenous
sphere with mass 6e24 kg, the angular momentum of the earth
(rotational inertia = 2/5 mr^2, and angular velocity = 2pi/86400s) is
about 6e33 kgm^2/s.  Total angular momentum is conserved, so the
spinning of the earth slows down by about 1 part in 1e16.  If they
were all to continue their hike for a year, that year would be
lengthened by a few nanoseconds (a few billionths of a second).  Not
measureable.

The world would slow down (or speed up) as they all took their step,
then be restored when they stopped. As racecar said, the effect would
be unmeasurable but that matters not to the principle. In fact, you
don?t need the entire population of China do the sums -- move your
hand, deflect an electron, any mass movement, even shining a torch.

One may consider that such diminishingly small effects are
inconsequential. Not so. Extrapolation to limiting conditions is an
invaluable tool for qualitative analysis and furnishes perspective on
physical phenomenon. On this basis, by General Relativity, the
movement of mass will have a permanent effect because it will have
altered time.

An example of the insight from such extreme thinking. Roll a coin
across a table. The momentum of that coin (on best current theory) is
infinitely greater than the momentum of the whole universe. I find
such revelation majestic and profoundly spiritual -- so far beyond
religion, and simplistic philosophies so redolent in, for example,
presidential elections.

Best