“Accelerate” in this context is what Noam Chomsky would call an example of a scientific symbol. It is not used according to its common sense understanding. Your English teacher and your friend are both right in the sense that if you told a person who was not a physics teacher that a car slowing down was accelerating, you would be considered a liar. Other examples of the same phenomenon are “work” (in physics, having a fun game of baseball is a lot of work, but holding a box motionless is not work, even if it makes you tired) and “sunrise” (which is a perfectly comprehensible word, even though scientifically speaking, the sun does not rise.)
Yeah, but don’t be surprised when they don’t believe you (like your English teacher). And don’t be surprised when they pull out a dictionary, and it seems to contradict you (like your English teacher did).
By the way, you’d think an English teacher should realize that words can have different definitions in a technical field than they do colloquially (too lazy to check the spelling on that. Sorry if it’s wrong). Your English teacher was wrong if she said that the dictionary definition meant that your physics teacher was wrong. Your physics teacher was correct that in physics, deceleration is a form of acceleration.
It is too clear, and so it is hard to see.
To sum up what the earlier posts were saying:
In Newtonian Mechanics,acceleration means any change in the velocity vector. Accelaration (i.e. the rate of change of the velocity vector) occurs when the magnitude of the vector increases and when it decreases. It even occurs when the magnitude of the vector remains constant while the position changes, as in the circular motion with a constant velocity that Water2j was talking about.
However in the everyday world we seem to use acceleration to mean increase in speed and deceleration to mean decrease in speed. These are the terms I would use outside of a formal discussion on mechanics.
BTW, Lexicon, I was a little snippy with you on the Matrix thread. I apologize.
Perked Ears indicate curiosity - Know Your Cat
Hmm…I’ve never heard anyone refer to the velocity of light. c is invariably, in my experience, referred to as the speed of light.
OT: I was in an academic competition once where we were asked ‘what is given by velocity times time?’ I answered ‘displacement’ - the proper answer. The answer they were looking for was ‘distance’. Apparently the question was written as ‘vt’ and the quizmaster had read ‘v’ as ‘velocity’ rather than ‘speed’.
Eschew Obfuscation
Chronos
Surely the only component of an object’s escape speed which plays a role in escaping the gravity well is that which acts directly out of the well. Speed with a direction is a vector, so “escape velocity” should be called “escape velocity”.
Granted many such escape velocities will exist, all pointing in different directions away from the centre of the earth, and they will all have the same magnitude, but each one is a vector.
Russell
You are accellerating when you slow down. Its just NEGATIVE acceleration.
Acceleration, as pointed out a couple times above, is a vector. There’s not really such a thing as a negative vector. It’s just a vector in the opposite direction. If you are travelling east, and slowing down, your acceleration vector is pointing west and has a positive value. You could also call it a negative value and pointing east, but that’s not the way it’s usually thought of.
Since force equals mass times acceleration, it’s often easiest to have the acceleration vector pointing the same way as the the force, regardless of what the motion might be at the time. When throwing a ball in the air, it’s easiest to think of it as constantly accelerating downward at 32.2 feet per second per second, rather than accelerating upward at negative 32.2 feet per second per second, then switching to accelerating downward at 32.2 feet per second per second.
Rather than tossing positive and negative around, it’s far more accurate (in physics) to think of decceleration as acceleration in the direction opposite the motion. Trust me that it’s easier to do the math that way.
m3
Do try to use the same spelling throughout your insightful posts.
You are correct, of course. Unless you want to be picky, in which case we should refer to acceleration with negative magnitude.
Other people in the thread who have earlier agreed with you point are - Zor, waterj2, RussellM, Lexicon, ZenBeam
Russell
No problem, Larry. I am pretty thick skinned when it comes to that sort of thing.
So I am glad that we’re cool.
Thanks.
I think that we’ll (my friend and I) will agree that we’re both right, in different ways and lay the issue to rest.
Sounds good.
Thanks again.
Once again, I love this site. It’s more addictive than caramel covered crack.
“Winners never quit and quitters never win, but those who never win and never quit are idiots.”
And to make it worse, since velocity includes direction, not only are speeding up and slowing down both accelerating, but so it turning. You turn, you change direction, you change velocity, ergo acceleration. So you really have three accelerators in your car: the gas pedal, the brake pedal, and the steering wheel. All right, four, if you want to count the emergency brake.
If you look above, I did go into detail about cars and turning and how that is also acceleration.
I don’t see what the semantic problem is at all here. Think about it…When you accelerate backwards (ie, slow down), you’re really just adding backwards speed. When you accelerate left, you’re adding “left” speed. It all works out just fine. Turning is NOT acceleration. If I am running straight ahead, and turn so that I am facing sidways, but still running in the same direction that I started in, I have NOT accelerated. It is the actual MOVEMENT in the new direction that is the acceleration.
Truth does not change because it is, or is not, beleived by a majority of the people.
-Giordano Bruno
Yes Flymaster, but they are talking about turning in a car, which involves the wheels pushing on the ground and making the car go in a different direction, not just rotating but continuing motion linearly.
water2j: No such thing as a negative vector? Sure there is. If it goes in the negative direction (i.e., not positive), it’s a negative vector.
What’s negative? Luckily, we determine the orientation of our axis, and thus determine what’s negative and what’s positive. It’s completely arbitrary. In fact, sometimes assigning down to be positive is easier for solving problems, even though it’s counter-intuitive.
I can’t count the number of times I’ve written “-mg” or “-v” this semester. Both are vectors (one is acceleration, the other is velocity), and in those cases, both are negative.
Yeah, I just wanted to be a little more explicit.
Acceletation (a vector) is the derivitive of the velocity (also a vector) with respect to time. There is a technical term for the scalar derivitive of the scalar speed with respect to time; it’s called the “pickup”, but it’s rarely used in science. Sometimes you will hear someone say a car has good pickup. Whether they know it or not, they are using the word in the technical sense.
Another point: it’s probably best not to ask your English teacher about technical terms, nor you science teacher about the general use of English. Many of the words used in a technical sense (Energy, Power, Pressure, Work, Potential, etc.) have non-technical uses. Some pedantic scientists attempt to ban non-technical uses of these words, but the fact is that the non-technical uses of these words predates the technical uses in almost every case.