Here, “demonstrations” and “experiments” mean the same thing: showing someone a scientific phenomenon, like “frying an egg with liquid nitrogen” Strictly, they are different. “Demonstration” means I know what happens and I want to show you. No surprises in the result. “Experiment” means to try something new and find out what happens. We might both be surprised at the outcome.

A demonstration is showing how something works or is made. For example, cooking demonstrations will teach you how to cook something (frying egg with liquid nitrogen for example!). In your sentence, the demonstrations will teach people about science. Demonstration also has another definition which means to protest or march against something, usually political. But in your context, it means to show how something works or is made/completed.

I dont understand the question. I think you are confusing demonstrations - like protests, or strikes or riots with demonstrations that are like someone demonstrating how something works. demonstrating how an experiment worked.