Motion and rest

Make a list of things that are moving and things that are not. Your book's examples: a cow grazing in a field is in motion; a tree is at rest. But how do we decide?

An object is in motion if its position changes with respect to a reference point, with time. If its position does not change with respect to the reference point, it is at rest. The cow keeps changing its place in the field: motion. The tree stays where it is: rest.

Now Deepa is in a bus. All the passengers sit in their seats; a minute later they are still in the same seats. Their position has not changed with respect to the bus. With the bus (or Deepa) as the reference point, the passengers are at rest.

But look out of the window. The passengers and the bus keep changing their position compared with things outside. With a building outside as the reference point, the passengers are in motion.

So the reference point matters. The same passenger is at rest compared with the bus and in motion compared with the road. And Padma, on her bus to Delhi, is in motion with respect to Delhi: her distance from it keeps changing.