Final answer:
The force that knocks an object moving forward sideways is an external force, as described by Newton's first law of motion. This could be due to a collision, friction, or other forces changing the object's direction, like the effect felt during a sharp turn in a car.
Step-by-step explanation:
The force you are asking about, when an object moving forward gets knocked sideways, is typically called an external force. In accordance with Newton's first law of motion, which states that an object will maintain its state of motion unless acted upon by a net external force, this sideways force changes the object's state of motion. In real-world situations, several forces can act as this external force, such as friction, tension, normal force, or even another object colliding with the one in motion.
For example, if an object like a rolling ball is knocked sideways by another ball, the sideways force is the result of the collision between the two balls. This changes the direction of the ball's momentum, creating a new motion path. Similarly, when a car makes a sharp turn, the force exerted by the friction between the tires and the road surface is what changes the direction of the car's velocity. This is why you might feel a force pushing you sideways in the seat, often referred to as a centrifugal effect, which is in fact the inertia of your body wanting to continue in a straight line.