In the latter case the resistance is caused by dissipation of mechanical energy when the configuration or the direction of flow is sharply changed, by the formation of vortices and secondary flows as a result of the flow breaking away, by the centrifugal forces, etc.
Animals depend on plants for food as plants produce food and energy which animals can't, so, herbivores eat plants to get energy, carnivores eat herbivores and other carnivores for energy and omnivores eat all four, plants, herbivores, carnivores and also other omnivores for energy.
Plants need energy to survive just like you, but they get their energy directly from the sun. Plants are producers. Producers are living things that can make their own food using air, light, soil, and water. Plants use a process called photosynthesis to make food. Only plants can produce their own food. That's why they are called producers. Animals that eat only plants are called herbivores. Herbivores are consumers because they eat plants to survive. Deer, grasshoppers, and rabbits are all consumers.