Newton’s second law of what is more than a definition; it is a relationship among acceleration, force, and mass?
interference
gravity
change
motion
9.80 m/s 2 . When we say that an acceleration is 45 g 's, it is 45×9.80 m/s 2 , which is approximately 440 m/s 2 . ) While living subjects are not used any more, land speeds of 10,000 km/h have been obtained with rocket sleds. In this example, as in the preceding one, the system of interest is obvious. We will see in later examples that choosing the system of interest is crucial—and the choice is not always obvious. Newton’s second law of motion is more than a definition; it is a relationship among acceleration, force, and mass. It can help us make predictions. Each of those physical quantities can be defined independently, so the second law tells us something basic and universal about nature. The next section introduces the third and final law of motion.