0
$\begingroup$

I am studying for the CAP physics contest and came across this question:

"You are holding a bottle of pop in your hands on a bus. The bubbles in the pop are going straight up. Suddenly, the bus brakes hard to avoid a road hazard. How is the motion of the bubbles in the pop affected?"

I believed that since the bubbles are moving forward in their intertidal frame of reference, that they would move backwards in the drink. However, the answer is they would move towards the front of the bus. I was hoping someone would be able to help me understand why?

$\endgroup$

marked as duplicate by sammy gerbil, Yashas, John Rennie newtonian-mechanics Apr 6 '17 at 5:51

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • $\begingroup$ Like the balloon in the linked question (which floats in a denser medium) the bubbles move forward if the bus accelerates and backward if the bus decelerates. I think the given answer must be wrong. If this is the official answer to a public examination, it is highly unusual for it to be incorrect. Please confirm exact wording of question and origin of answer. $\endgroup$ – sammy gerbil Apr 6 '17 at 11:34
  • $\begingroup$ I have checked the official solution on the University of British Colombia website. The question is #5 on the 2016 CAP examination. Options are a-d. The official answer is d - the bubbles move towards the back of the bus. $\endgroup$ – sammy gerbil Apr 7 '17 at 20:28
0
$\begingroup$

Just think of what you experience when the bus breaks. You break your nose if you don't have your seatbelt on.

So for sure the bubbles would go forward, because they keep moving and the bus is the thing that "goes back". I would add that the bubbles keep going up, as the force in the vertical frame would be the same with or without the bus braking.

$\endgroup$

Not the answer you're looking for? Browse other questions tagged or ask your own question.