Big Idea: Light travels in straight lines and when it hits a surface it is either absorbed or reflected. If it is absorbed, the light can cause it heat up. If it is reflected, the colour that is reflected is the colour we see.
The demonstration shows how black things absorb all colour and therefore get warm. Something that is white reflects all light and therefore does not absorb any of the light, so it stays cool.
Other demonstrations show how light that is travelling in straight lines, can be reflected inside a trail of water, giving it the illusion of bending. But it is not really bending, it is bouncing off the inside of the water stream.
A camera obscura works because it allows the light to travel from the source through hole and to the inside of the box. It appears upside down because the top of the object is above the hole and since a straight line through the hole means the light arrives on the back wall of the box, below the hole.