Final answer:
The four theorists impacting physical development are Sigmund Freud, with his psychosexual theory, Erik Erikson and his psychosocial theory, Jean Piaget with his focus on cognitive development, and Lawrence Kohlberg's theory of moral development.
Step-by-step explanation:
Four theorists who have significantly impacted our understanding of physical development are Sigmund Freud, Erik Erikson, Jean Piaget, and Lawrence Kohlberg. Freud is known for his psychosexual theory of development, where he believed that our energy is focused on specific erogenous zones at different stages of development. Erikson modified Freud's ideas with his psychosocial theory of development, highlighting the importance of social interactions in shaping our ego identity and personality throughout our lifespan. Piaget is renowned for his theory of cognitive development, which asserts that children progress through a series of stage-specific ways of thinking. Lastly, Kohlberg focused on moral development and proposed that our moral reasoning evolves through three levels that build on our cognitive development.