Timeline for is a positive acceleration indication that velocity must be positive?
Current License: CC BY-SA 4.0
10 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Jun 2, 2021 at 11:09 | vote | accept | Adham Hussin | ||
| Jun 2, 2021 at 11:06 | vote | accept | Adham Hussin | ||
| Jun 2, 2021 at 11:09 | |||||
| Jun 2, 2021 at 4:57 | comment | added | DKNguyen | When the equation spits a number at you, the sign either tells you that your assigned direction for the unknown is opposite of the true direction or it outright tells you the true direction depending on how you went about assigning your unknowns. If choose to assign all unknowns in the positive direction then the polarity of the result gives you the direction. But if you assign unknowns with the direction you think they will be, you are pre-assigning directions and the polarity of the result tells you if your guess was correct or not. Either approach is identical mathematically. | |
| Jun 2, 2021 at 4:56 | comment | added | DKNguyen | Just because the author deemed the problem simple enough to not need to explicitly define a coordinate system doesn't mean it's not there. In English you might say 20m/s to the left and 10ms/ to the right, but if you are defining things using conventional cartesian coordinates the way you put it into the equations is you say -20m/s and +10m/s because "left" and "right" don't mean anything mathematically. It's synonymous. | |
| Jun 2, 2021 at 4:15 | comment | added | DKNguyen | @r13 You're not being rigorous and are mistaking scalars and magnitudes for vectors. Speed is a scalar, velocity are vectors. Vectors have direction based on an coordinate system (the simplest being vectors in a one dimensional problem like an elevator problem or the OP's problem). Try your approach in an elevator problem, a problem with multiple objects, or with unknowns where you don't know some of the directions ahead of time. Just throw in two particles moving in opposite directions and your approach breaks down mathematically. | |
| Jun 2, 2021 at 3:40 | comment | added | r13 | A driver has reduced his speed from 120 mph to 90 mph, it is a speed change of -30 mph, but we won't call the velocity is -30 mph during the deceleration. Same as you back up your car at a speed of 5 mph, we won't say you drive the car with a velocity of -5 mph. Velocity is always positive, direction does not matter. | |
| Jun 2, 2021 at 3:27 | comment | added | DKNguyen | If your velocity and acceleration are different polarities, it means you're decelerating (or accelerating in the opposite direction of your movement, same thing). If they have the same polarity then you ace accelerating (in the same direction as your movement. Whether your velocity is negative or positive just tells you what direction in your coordinate system you are moving in. And same with the acceleration. Negative and positive have no inherent meaning except that they are opposites of each other. | |
| Jun 2, 2021 at 3:21 | comment | added | DKNguyen | Velocity is a vector and so is acceleration. So you can define your coordinate axis positive and negative directions to be anything you want, left or right, up or down. The polarity of the velocity and acceleration vectors just follows whatever coordinate system you defined. All negative means is "opposite of the direction you defined as positive". | |
| Jun 2, 2021 at 3:17 | comment | added | r13 | As a symbol, "a" can have a negative sign to indicate deceleration, which does not have its own symbol. My question is, does negative velocity exist (what does -30 mph mean)? | |
| Jun 1, 2021 at 21:17 | history | answered | DKNguyen | CC BY-SA 4.0 |