Answer
When the ball hits the floor, exerting a downward force on it, the floor exerts an equal force upward on the ball. The force exerted by the floor on the ball changes its velocity and causes it to bounce.
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.