Sound words, also known as onomatopoeia, can make a poem or piece of writing appeal to the sense of hearing. They include words like bam, whoosh or slap. Take a look at five categories of onomatopoeic examples, grouped by letter combinations that are commonly used to represent certain sounds.
Free verse poems will have no set meter, which is the rhythm of the words, no rhyme scheme, or any particular structure. Some poets would find this liberating, being able to whimsically change your mind, while others feel like they could not do a good job in that manner. Robert Frost commented that writing free verse was like "playing tennis without a net."