Newton’s Second Law of Motion

Key Concepts:

• The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass.
• Equation: F = ma (F = net force, m = mass, a = acceleration)
• SI unit of force: newton (N) = force required to accelerate 1-kg mass at 1 m/s²
• Used to solve motion problems (acceleration, force, distance traveled)
• Defines momentum (product of mass and velocity)
• Impulse of a force = force × time = change in momentum
• Momentum is conserved (total momentum of a closed system remains constant)

Newton’s Third Law of Motion

Key Concepts:

• For every action, there is an equal and opposite reaction.
• Equation: F_action = -F_reaction (F_action = force from first object on second, F_reaction = force from second object on first)
• Used to solve problems involving interactions between objects (forces exerted, motion)
• Explains phenomena like walking (ground pushing back on foot propels person forward)
• Balanced forces: net force on an object is zero, no acceleration