9. Write down Newton's second law of motion.

Newton's second law of motion states that the acceleration of an object is directly proportional to the net force acting upon it and inversely proportional to its mass. Mathematically, it's expressed as F = ma, where F is the force, m is the mass, and a is the acceleration. This law explains how the velocity of an object changes when subjected to external forces. In real-world applications, this law can be seen in action when you push a shopping cart. The harder you push (more force), the faster the cart accelerates. However, if the cart is loaded with heavy groceries (more mass), you’ll need to apply a greater force to achieve the same acceleration. This principle is fundamental in engineering, sports, and countless daily activities where forces interact with mass.