Final answer:
Newton’s cradle is almost ideal as a closed system because its design limits energy and momentum loss, despite minor losses from air resistance, friction, and inelastic collisions.
Step-by-step explanation:
Newton’s cradle is described as an “almost-ideal” closed system because it is designed to demonstrate the conservation of momentum and energy with minimal external interference. In an ideal closed system, there would be no loss of energy or momentum to the environment; however, in the case of Newton’s cradle, some energy is lost due to air resistance and friction at the points where the balls are connected. Additionally, the balls themselves are not perfectly elastic, so some energy is also lost to sound and heat upon collision.
Despite these losses, Newton’s cradle is a good approximation of a closed system because the main forces acting are internal, like the tension in the strings and the forces of collision between the balls, mimicking an idealized environment where external influences are negligible. The system continues to function with minimal external force or energy being added, closely resembling isolated conditions that are assumed in theoretical physics.