A traffic fanatic wants to estimate the maximum number of cars that can safely travel on a particular road at a given speed. She assumes that each car is 18 feet long, travels at speed s, and follows the car in front of it at a safe distance for that speed. She finds that the number N of cars that can pass a given spot per minute is modeled by the function N(s)

car stops. he keeps going = he has inertia

the aurora is formed when charged particles emitted from the sun during a solar flare penetrate the earth's magnetic shield and collide with atoms and molecules in our atmosphere. these collisions result in countless little bursts of light, called photons, which make up the aurora.

auroras are generated by charged solar particles hitting molecules in earth's atmosphere. this usually happens in high latitudes, because our planet’s magnetic field tends to funnel these particles toward the poles. that’s why it can be experienced in northern ohio.

one "light year" is the distance that light travels, through vacuum, in one julian year.   that's 365.25 days, of 24 hours each.