Let’s say you are on a moving bus. When you change its speed, you lean forward in the direction of the bus. Is the frame of reference associated with the bus inertial in this case?
The law of inertia is fulfilled in reference systems related to the Earth and the bus if the bus moves in a straight line and evenly. In this case, the speed of the bus decreases, therefore, the frame of reference is not inertial.
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