1. The problem statement, all variables and given/known data I am a bit confused about what are inertial reference frames and what is not. The text states: "We define an inertial reference frame as a reference frame in which Newton's laws are valid.... Accelerating reference frames are not inertial reference frames. Consequently, Newton's laws are not valid in a reference frame attached to an accelerating object. ...... In Chapter 4 we defined inertial reference frames to be those reference frames moving with constant velocity." Would someone mind explaining the reasoning to these answers a bit better, and make sure my reasoning is correct. 3. The attempt at a solution Are the following inertial reference frames? Yes or No. A car driving at a stead speed on a straight and level road. ~ Yes I understand this one because the car is moving at a constant velocity so it is an inertial reference frame. A car driving at a steady speed up a 10 degree incline. ~ Yes The car is moving at a constant velocity so it is an inertial reference frame. A car speeding up after leaving a stop sign. ~ No The car is accelerating so it is not an inertial reference frame. A car driving at steady speed around a curve. ??? I found the answer to be no, but I do not understand why. If it is moving at a constant speed shouldn't it be an inertial reference frame. A hot air balloon rising straight up at steady speed. ~ Yes Constant velocity so inertial reference frame. A skydiver just after leaping out of a plane. ~ No Not positive, but I think on this one its just because they are accelerating in free fall. The space shuttle orbiting the earth. ~ ??? I know the answer is no, but I am not sure exactly why.