Examples of strong verbs are "give," "stick," "tell" and "wear." The difference between strong and weak verbs is the way the past tense is formed. Weak verbs add an ending, such as -ed, -d or -t, to the present tense of the verb, while strong verbs typically change the vowel.
Strong verbs are also known as irregular verbs. Weak verbs are also known as regular verbs. Irregular verbs are referred to as strong because they form the past tense within their original letters, instead of needing additional letters added.
There are various ways strong verbs change from present to past tense. An example of the vowel change is in the present tense strong verb "give," which turns into the past tense "gave."