What 2 things bones come together

According to the loco mass the mass of reactants and products

Johnny rode his bike to a friend's house 4 blocks down the street in his neighborhood. he immediately rode back home once he realized his friend was not able to play. what was his displacement for the total bike ride? how did you determine this? what could we use as a reference point to determine he was in motion during his bike ride? why can you use it as a reference point

There are fewer than 100 naturally occurring elements in the universe, but there are millions of different unified substances. explain how this can be true.