Final answer:
The transfer of heat from a warm hand to 70°F water is an example of conduction, which is heat transfer through direct contact.
Step-by-step explanation:
When a warm hand is immersed in water that is 70°F (21°C), the heat is transferred from the hand to the water through a process called conduction. Conduction is the transfer of heat by two objects that are in direct contact with one another. In the given scenario, the heat from the hand directly warms the water it is touching. This is similar to the example of holding a hot cup of coffee, where the heat transfers into your hands through the mug, or when a barista steams milk, transferring heat through the process of convection; however, in the case of the hand in water, it is conduction that is responsible for the heat transfer.