An astronomical unit is
the mass of the sun
10 light-years
the distance from earth to the sun
the diameter of the earth

according to newton's 3rd law of motion, if you hit a baseball with a bat it will
hurt your hand from the reaction force
accelerate according to the applied force
fly in a straight line unless an outside force changes its course
fall to the ground because of gravitational pull

the pull of the moon on earth's tidal bulge is causing
the earth to gradually rotate faster
the earth to slowly expand in size
the earth to rotate slightly slower
the moon to move closer to earth