How does a shadow appear for an object which is already in a shadow of another bigger object?
If the smaller object is in the shadow, then how is it visible in the first place? To answer these questions, we need to review the way in which light or any other Electro Magnetic Radiation (EMR) interacts with matter.
Light (or any EMR in general) on interaction with matter can either get transmitted, reflected or absorbed or all the above in different proportions. When a material does not transmit light through it, a region of darkness is formed to the side, opposite the source of light, called a shadow.
This can happen only when there is a single source of light and the rays travel coherently like in a laser. In the case under study, the light from sun gets scattered (reflected in all directions) by the objects nearby the tree.
These light rays hit the scooter and get reflected to the eyes of the observer, hence the smaller object is visible. Some of these rays do fall on the shadowed portion of the tree too.
In the same lines, since the smaller object is another opaque body, it does not transmit light through it and hence casts a shadow, however of lesser intensity.
We see this diffused shadow since the smaller object obstructs the light (reflected from neighbouring objects) from falling on the ground which would have otherwise happened.Since the light impinging on the smaller object is from varied sources (scattered from nearby objects) and from different directions, the shadow is rather diffused and scarcely takes the outline of the object.
It is useful to recall that, objects like air, interact with light differently wherein they scatter and absorb minimally and transmit a larger percentage of incoming radiation and thus we do not see shadows of air. However we see shadows of clouds as they scatter away much of the incoming radiation while transmitting a little.