3 ms·

It's true that the horizontal energy doesn't change and it keeps going to the right but it stays in the air for less and less on each bounce and travels a short

It's true that the horizontal energy doesn't change and it keeps going to the right but it stays in the air for less and less on each bounce and travels a shorter and shorter distance on each bounce assuming the ball only goes forward when it bounces but you still didn't answer the question because if you sum the total time the ball will spend in the air you will get a finite number so the ball will travel a finite distance which is a much better description of what happens to the ball than just saying it keeps going to the right.

mfukar 16y ago
The problem statement says 'ignore friction'. Doesn't that imply the ball's initial energy (when thrown, presumably, but it doesn't matter) is conserved? How, then, will it travel a finite distance, since we are not told of any obstacles?
- utoku 16y ago
  The problems with questions in imagined worlds is that sometimes it is hard to get the premises right. Even if you treat the problem as a thought experiment, it feels uncomfortable because: - Ball bouncing with 60% energy remaining all the time is actually a premise, a rule, because we are not supposed to consider atoms or their interactions. There is no reason to it, it becomes a fact. - Ball is a singular object. We don't have atoms, so we don't have to think things like "What happens when the height of the bounce gets shorter than the size of the atom?" The concept of the ball becomes a premise. - We get a picture that shows the balls losing speed in direction x at each bounce, but since the question asks for us to judge "qualitatively", we will omit that. We cannot have observations for this problem, it is not the real world. - There is no friction, or spin, so vertical speed cannot be transfered into horizontal speed and vice versa. - The concept of bounce might be different, this question probably assumes it happens at 0 (instant) time without deforming the ball, since remember our ball is singular. - The rest we can probably treat with Newtonian physics in Euclidean geometry, no air, interaction between ball and surface frictionless, etc. But it feels uncomfortable, because I too can make up an imaginary world for myself, dress it like the real world and ask my question and hide the premises behind.
  - mfukar 16y ago
    I'm not sure what you're trying to say. I understand you might feel 'uncomfortable' hiding electromagnetic forces and quantum mechanics behind Newtonian physics (how so?), but how's that relevant to the problem, or its answer?

mfukar 16y ago

The problem statement says 'ignore friction'. Doesn't that imply the ball's initial energy (when thrown, presumably, but it doesn't matter) is conserved? How, then, will it travel a finite distance, since we are not told of any obstacles?

utoku 16y ago
The problems with questions in imagined worlds is that sometimes it is hard to get the premises right. Even if you treat the problem as a thought experiment, it feels uncomfortable because: - Ball bouncing with 60% energy remaining all the time is actually a premise, a rule, because we are not supposed to consider atoms or their interactions. There is no reason to it, it becomes a fact. - Ball is a singular object. We don't have atoms, so we don't have to think things like "What happens when the height of the bounce gets shorter than the size of the atom?" The concept of the ball becomes a premise. - We get a picture that shows the balls losing speed in direction x at each bounce, but since the question asks for us to judge "qualitatively", we will omit that. We cannot have observations for this problem, it is not the real world. - There is no friction, or spin, so vertical speed cannot be transfered into horizontal speed and vice versa. - The concept of bounce might be different, this question probably assumes it happens at 0 (instant) time without deforming the ball, since remember our ball is singular. - The rest we can probably treat with Newtonian physics in Euclidean geometry, no air, interaction between ball and surface frictionless, etc. But it feels uncomfortable, because I too can make up an imaginary world for myself, dress it like the real world and ask my question and hide the premises behind.
- mfukar 16y ago
  I'm not sure what you're trying to say. I understand you might feel 'uncomfortable' hiding electromagnetic forces and quantum mechanics behind Newtonian physics (how so?), but how's that relevant to the problem, or its answer?