Q:  How fast does the Earth move in its orbit
           around the Sun?



      (Hint: it travels a circle of radius 1 AU (= 150 million km) in 1 year)


      (Hint: there are about 3.14 x 10^7 seconds in a year)


    
      The distance travelled by the Earth is the circumference of its
    orbit, which is

            distance  =  2 * pi * R   =   2 * 3.14 * 150 x 10^6  km

                      =  9.42 x 10^8  km


      The speed of the Earth in its orbit is the distance travelled 
    divided by the time it takes:

                               distance       9.42 x 10^8 km
           Earth's speed   =  -----------  =  ---------------
                                 time         3.14 x 10^7 s

 
                           =  30 km/s   =  30,000 m/s


      So the speed of the Earth in its orbit is tens of thousands of meters
    per second, and other planets travel with similar speeds.  But the
    speed of the Sun, in response to the gravitation pull of Jupiter,
    is only 12 meters per second.

      Not 12,000 meters per second.  Just 12.

      The Sun moves very slowly in response, because it is so much more
    massive than Jupiter, or any other body.