18. A Force is a push or a pull. There are natural forces such as the one between two surfaces that rub, called____ Another force is gravity, that pulls us to the center of the Earth.
Many forces can be found acting on the same object. When two forces act in the same direction, we_____ the forces to find _____the force. This causes _____the forces are in the movement of the object. speed up, slow down, change direction or
19. An inclined plane is often called a_____ - It is a_____