Question

Let's say there is a roller skater standing in the aisle of a bus that begins to accelerate. The roller skater will begin to roll backwards. The seated passengers will feel like they are being pushed into their seats. There is also a non moving observer watching the scene from the sidewalk. What are the inertial and noninertial frames of reference (of the sidewalk observer, the skater, the passengers, the bus)? Why? Thanks for your help!

Answer 1

An inertial frame of reference refers to a frame that is not accelerating.
A noninertial frame of reference refers to a frame that is accelerating.

The bus in this case is accelerating.

The people on the bus will, therefore, accelerate. So, the rollerskater and the people in the seats will be in noninertial frames of reference.

The person on the sidewalk is not accelerating, therefore he/she is in an inertial frame of reference.


To be more specific as to what is happening... the rollerskater and the people in the seats are experiencing a force that is not real in the typical sense of a force. This is sometimes referred to as a pseudoforce. A pseudoforce is a consequence of an accelerated frame of reference. In this case, this specific pseudoforce is called the inertial force.

However, the observer on the sidewalk will not see this force.