This is a question that we often get from sitter and owners who work with Rover. Help the community out by answering them in our forum!
Just like some people, dogs can get car or motion sickness when riding in a car. For people, one part of your balance-sensing system such as your inner ear, eyes, and sensory nerves senses that your body is moving, but the other parts don't. I don't know if that is the same for dogs. My pup gets car sick on trips sometimes. A veterinarian can prescribe medication. I add a little "ginger tea" (fresh ginger boiled in water, and cooled) to his water. The morning of our trip, he gets his "ginger water tea" but is either fed several hours before we leave or isn't fed. When we stop for breaks I give him a very small treat or a little kibble. I also take him on frequent short trips around town when running errands to places he can go inside, to help.