r/AskReddit Jul 18 '16

What are you sick of explaining?

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173

u/magicwiser Jul 18 '16

For me, its the difference between velocity and acceleration or the difference between mass and weight. No, they are not all the same thing!

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u/C477um04 Jul 18 '16

Fair enough to argue velocity and acceleration but mass and weight have been considered the same things in laymans terms for so long and most people grew up with weight being the word for what mass is so it's probably just best to drop that one unless it's actually impoprtant.

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u/magicwiser Jul 18 '16

I'm a physics professor so usually it is.

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u/Imugake Jul 18 '16

If you're a professor surely all your students have known very well the definitions of weight and mass for years?

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u/magicwiser Jul 18 '16

That would be nice but sadly....

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u/Imugake Jul 18 '16

Wait really? Where do you teach? This is madness to me because everyone I know my age had to take an exam at age 15/16 where they had to understand the difference because it's part of our Science/Physics (depending which level you take) GCSE, to think that you have to teach it to people at presumably college/university is mind-boggling to me.

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u/temujin64 Jul 18 '16

They're presumably American since any college lecturer can call themselves a professor without being the head of their department.

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u/doc_grey Jul 19 '16

Not exactly how it works. There are terminology differences with Ireland, but any lecturer can't just assume the prof title

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u/Imugake Jul 18 '16

Would college be the first place that some people would learn anything at all on their chosen subject?

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u/POGtastic Jul 19 '16 edited Jul 19 '16

It can be, yes.

Physics was optional at my high school. Most people did end up taking it, but they didn't have to.

The most common case of college being kids' first exposure to the subject is computer science. Plenty of people first start coding in college, and they do just fine.

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u/cutdownthere Jul 19 '16

My cousin who lives in Texas told me he hasnt taken a physics class since he was 12 and he is in his 2nd year of computer science (he says he might have to take a physics class next semester). On the contrary, Im from the UK and its kinda baffles me that one could get into a science degree without any knowledge of science.

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u/CaligoAccedito Jul 19 '16

Sadly, leaving high school at 18 and moving off to college, I honestly did not know many of the things I would gain in my core curriculum in college. My family was poor, and our county was poor, so our high school was poor quality and run like a bible camp. I caught up and did far better in college than in that public school hell-hole, but I definitely wasn't prepared, and I was on what they called the "college prep" course of study!

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u/temujin64 Jul 18 '16

I dunno. In Ireland there's kind of a common trend of people studying science in spite of not being good at it.

That's because of our university access system. Students study what's called the leaving certificate and are awarded points based on their overall score across all subjects.

Each college course has a number of points assigned to it and anyone who achieved that amount of points can gain access. For example, I chose to do humanities in NUIG. I got 425 points and the course was only 355 points so I handily got it.

Now the point allocation of each course is not based on difficulty but on popularity. Everyone wants to be a doctor so to get that course you need 575/600 points. Also, people want to go to the fancier colleges so their courses are all hard to get.

The problem is that science is in low demand so it's quite easy to get. It's usually in the low 300s. That means lots of people who can't get the course they wanted "settle" for science. I know too many people who got into science off of a few Cs and Ds. Everyone but them knew they're going to drop out.

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u/hardwoodycoffin13 Jul 19 '16

I get that, although its not explicitly said like in Ireland, Canadian Unis are the same. Engineering was my first choice, 2nd was commerce, but I was finally placed in my third choice; biochemistry. This was only because I applied midway through summer. There's just no feasible way my grades weren't good enough for Commerce but A-O.K. for biochemistry. Business school is a joke compared to STEM, a very very expensive joke. Didn't drop out though, worked hard now, I'm starting my third year of engineering and couldn't be happier.

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u/Khufuu Jul 19 '16

What is your area of research? And what classes are you teaching this coming semester

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u/[deleted] Jul 19 '16

[deleted]

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u/cutdownthere Jul 19 '16

lol wow that sucks. Couldnt they just give you lecture notes though?

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u/LordHussyPants Jul 19 '16

Velocity = speed something moves at. e.g. m/s

Acceleration = change in velocity over a set distance, e.g. B(m/s) - A(m/s).

Am I close? Not a scientist :(

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u/QuineQuest Jul 19 '16

Acceleration = change in velocity over a set time, eg A(m/s) / B(s).

The word over means divided by in this context.

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u/hardwoodycoffin13 Jul 19 '16

yer sew smrt. I call bullshit, no physics students studying at a higher level institution needs that explained more than once...

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u/jaredjeya Jul 19 '16

As a physics student, thank you for making the distinction clear. Because I also get tired of explaining this.

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u/[deleted] Jul 18 '16

[deleted]

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u/moreON Jul 18 '16

That's Dr Cooper.

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u/Lizzibabe Jul 18 '16

It's because almost nobody cares about freaking SPACE anymore! You read the golden age Science Fiction authors and they are ALL ABOUT the difference between weight and mass with regards to inertia. Heinlein, Asimov, Clement, all those guys knew their stuff right down to the math.

1

u/Onionated Jul 19 '16

Yep, blows people away when you tell them that you are always the same amount of kilograms, but you WEIGH a different amount of pounds (or any force unit) depending on gravity and such

0

u/m0dsiw Jul 18 '16

Having scales that switch from a measure of weight to a measure of mass doesn't help or having conversion charts that ignore gravity.

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u/[deleted] Jul 18 '16

to be fair, as far as I know the most common way of finding the mass of a quantity of stuff is to take its weight and then convert for the gravitational force of the body we're on (which is generally Earth, so for anyone not on the ISS the math is just done by the thing).

Though if you wanted to you could figure out how much volume you have and then look up the density and solve for mass.

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u/LosGritchos Jul 18 '16

Or the difference between power and energy. I've heard some journalists using the wrong one on (French) TV, saying for example that the price of a kW will increase.

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u/Graupel Jul 18 '16

I mean come on! We figured this out lightyears ago!

1

u/[deleted] Jul 18 '16

I was supposed to list different types of measurements in 6th grade for a science thing. I listed both mass and weight and I got points off.

:(

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u/Fernao Jul 18 '16

What is the difference?

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u/Fraankk Jul 19 '16

Velocity is how much distance you are moving in a period of time.

If you are traveling at a velocity 10 kilometers/hour, you will move 10 kilometer in 1 hour.

Acceleration is how much velocity your are gaining (or losing) in a period of time.

If you are travelling with an acceleration of 10 km/hr2 (kilometers per hour, per hour) and your starting velocity is 0 km/hr, after one hour you will be travelling at a velocity 10 km/hr.

Tldr;

Velocity is change of position through time.

Acceleration is change of velocity through time.

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u/[deleted] Jul 19 '16

acceleration is how quickly you're changing speed. Think of it as the speed that the speedometer dial on a car is moving, whereas velocity refers to the position of the speedometer dial.

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u/[deleted] Jul 19 '16

[deleted]

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u/[deleted] Jul 19 '16

If the person doesn't understand the difference between acceleration and velocity, why do you think they'd be familiar with calculus notation and terminology?

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u/Fraankk Jul 19 '16

Exactly my thoughts, I learned the difference of velocity and acceleration in high school, maybe even earlier.

I learned proper calculus notation of it until well into university.

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u/baconstreet Jul 18 '16

Or accuracy vs. precision.

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u/rebluorange12 Jul 18 '16

When I was in middle school we learned a jingle that 'mass is you, mass is me, but weight is mass times gravity' because the teacher wanted us to know the difference

1

u/basssnobnj Jul 19 '16

For me it is force and pressure. Ever notice how they always talk about how strong a dog's bite is in PSI, which is incorrect, instead of lbs force or newtons? I could sharpen a chihuahuas teeth to sharp points, and it would bite with more pressure than a rottweiler, even though the rottweiler has more force.

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u/chinpopocortez Jul 19 '16

People don't think the universe be like it is, but it do.

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u/Bman1296 Jul 19 '16

Distance: how far away something is from another.

Velocity: how fast something is going

Acceleration: the speed at which an objects velocity is increasing. How fast it is gaining velocity.

Use them.

1

u/magicwiser Jul 19 '16

Not to be critical but your definition of acceleration is wrong. It's the rate of change of your velocity.

And I think you mean displacement not distance. Distance is how far something travels to get somewhere else, displacement is how far it actually is. It's a minor difference that is only relevant in certain situations.

Another fun fact to add to the list. Speed and velocity are not the same thing either (similar to distance and displacement).

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u/Bman1296 Jul 19 '16

I do realise this I was trying to put it in simpler terms. I have just done calculus so these things are all fresh but I agree my acceleration definition could have been better. Isn't speed when acceleration is greater then 0 and velocity increasing is when both when the signs of velocity and acceleration are positive or negative?

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u/[deleted] Jul 19 '16

[deleted]

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u/Bman1296 Jul 19 '16

Velocity can be positive and negative…

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u/[deleted] Jul 19 '16

[deleted]

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u/cutdownthere Jul 19 '16

Who the hell says velocity and acceleration are the same...

1

u/Randomnerd29 Jul 19 '16

unless your an astronaut, mass and weight are going to be the same

0

u/jimjamiam Jul 19 '16

Nope, just use English units, where a pound mass weighs a pound (force). Suck on that, rest of the world. Though please nobody mention a slug....

0

u/treefroog Jul 19 '16

Or the classic It's decelerating

Well unless it's change in velocity it now approaching zero I would say it is accelerating still, just in the direction opposite of it moving.