Final answer:
A force is an influence applied by one object to another, resulting in the latter's acceleration or deceleration, as described by Newton's second law of motion (Fnet = ma). An external force acts from outside a system, whereas internal forces act within. Newton's laws help in predicting acceleration due to net forces on mass.
Step-by-step explanation:
An influence applied by one object to another, which results in acceleration or deceleration of the second object, is known as a force. This is a fundamental concept in physics, specifically Newton's laws of motion. According to Newton's second law of motion, the acceleration (a) of an object as produced by a net force (Fnet) is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass (m) of the object. This relationship can be expressed as the equation Fnet = ma. We also consider forces like weight, which is the force of gravity acting on an object (W = mg) and friction, which is the force that opposes the motion of two objects sliding against each other.
An external force is one acting on a system from outside the system, as opposed to internal forces, which act between components within the system. For an object undergoing free fall, gravity is the sole external force acting on it, causing it to accelerate at approximately 9.8 m/s2. When multiple forces are acting on an object, the net force is the vector sum of the individual forces, influencing the acceleration as per Newton's second law.
To analyze the effect of forces on an object, we often use free-body diagrams, which help in visualizing the forces and their resultant acceleration. This supports the big idea that mass and net force are inevitably linked in determining an object's motion.