What is persuasive speech?

It is when you want to make others believe that what you are saying is totally true. For example, let's suppose that you are delivering a speech about "getting 10 years younger just by taking a pill for two weeks". Your audience may think that that is utterly impossible; nevertheless, you have to make them change their mind by using all your strategies, so that your audience, or part of your audience, will believe that you are right.