1. Taking a frame attached to Earth as inertial, which of the following objects cannot
have inertial frames attached to them, and which are inertial reference frames?
(a) A car moving at constant velocity
This involves constant velocity, so they are inertial reference frames. For this reason,
inertial frames are non-accelerated frames since they move with constant speed.
Because it is being acted upon by a net force that's creating an accelerated situation
and the fictitious force that many people experience when they're accelerating forwards.
(b) A car that is accelerating
Have accelerating reference frames that are non-inertial reference frames. So this
object cannot have inertial frames.
(c) An elevator in free fall
Have accelerating reference frames that are non-inertial reference frames. So this
object cannot have inertial frames.
(d) A space capsule orbiting Earth
Have accelerating reference frames that are non-inertial reference frames. Cannot be
an inertial frame because the earth is revolving around the sun. It also rotating about its
own axis.
(e) An elevator descending uniformly
This involves constant velocity. Hence, they are inertial reference frames.
2. 2. A woman was transporting an open box of cupcakes to a school party. The car in
front of her stopped suddenly; she applied her brakes immediately. She was wearing
her seat belt and suffered no physical harm (just a great deal of embarrassment),
but the cupcakes flew into the dashboard and became “smushcakes.” Explain what
happened.
We can generalize the given scenario with a definition of inertia. We can say that inertia
makes everything stay at rest until there is a force applied to change such a state. In the
given example, both bodies had an external force applied to them, which is one of the
car breaks. One body, the driver's, had an additional force, in the opposite direction,
cancel out the impact of changing the state of rest. If there wasn't a force canceling out
one of the impact, the driver would have ended up just like the cupcakes.