Final answer:
Simple machines change the size and direction of a force by applying the force at specific points of the lever arm or maintaining a constant angle between the lever arm and applied force.
Step-by-step explanation:
A simple machine can change the size and direction of a force by applying the force at the same point of the lever arm along the length of the lever or by maintaining the same angle between the lever arm and the applied force. This allows the force to be applied in the desired direction and magnitude, making it easier to perform work.