If we make a metal red hot, it emits light. This is called incandescent body

Pinhole camera and periscope are the two instruments which show that light travels in a straight line.

The image of the sun will remain same, still if we use different types of holes because the holes will act as pinhole camera and light moves in a straight path.

The motion possessed by the planets around the sun is circular motion.

The motion exhibited by a freely falling stone is rectilinear motion

Opaque objects do not allow light to pass through them. When an opaque object is placed in the path of light, then the light is obstructed by the object leading to the formation of a dark patch known as the shadow of that object, which can be taken on a screen placed behind it.
Shadow formation: To form a shadow, there must be (i) a light source (ii) a screen (iii) an opaque object placed between the light source and the screen. For shadow formation, we can follow the given steps
Step 1: Take an opaque object.
Step 2: Throw light on it from a light source.
Step 3: Put a screen behind the object. In this way, a shadow of an object can be obtained on the screen.
In this way, a shadow of an object can be obtained on the screen.

The shadow of the object cannot be caught if the screen and the object are very far from each other. This is the same case, the shadow of the football cannot be seen on the ground when it is kicked high in the air. This happens because if we take the object away and away from the screen, the image becomes smaller and smaller and a time comes when it disappears from the screen.

The motions of a wheel of a moving bicycle and a mark on the blade of a moving electric fan are different in the following ways.

The dark patch of light is known as a shadow which is formed when there is an opaque object in the path of light.
When an image is the reflection of light. By seeing image, we can identify the object but shadow can mislead you from actual object.

Shadow is just an absence of light at that place. Shadow is not affected by the colours of the object because the amount of light is preventing to pass, will remain same. The shadow is affected by the shape of the object only. If the object is large, the shadow will be large and vice-versa.

Yes, there are many things that could give a circular shadow if held in one way and a rectangular shadow, if held in another way, e.g. a cylindrical object, a pencil, a candle, etc.
(i) Getting a circular shadow of a candle (which is cylindrical in shape), when it is laid down horizontally

(ii) Getting a rectangular shadow of a candle while in standing or in vertical position.