straight line motion and force

[paulo1913]

Distance, speed, constant acceleration, motion time graphs (including gradients and simple areas), mass, force (push, pull, friction, weight, reaction)

 

i have had trouble understanding what these things are and how to calculate them so if someone could help me that would be great!

[blike]

That's a lot of information to request from people! Have you first exhausted the available resources on the subject (i.e. wikipedia, etc.)?

[Klaynos]

A good resource for this kind of thing is:

 

http://www.bbc.co.uk/schools/gcsebitesize/physics/forces_and_motion/

[Bignose]

That's a lot of information to request from people! Have you first exhausted the available resources on the subject (i.e. wikipedia, etc.)?

 

Or an Introduction to Physics text? I am positive your library has several to choose from.

[paulo1913]

thanks guys for being so helpful

[theCPE]

If you googled

 

classical mechanics

or

classical physics

or

newtonian physics

 

 

You would have ample reading material to understand all of those basic concepts.

[carol]

just want to ask, is velocity equal to displacement over change in time? that would mean, the average speed and the average velocity of a body could be completely different? why do we sometimes speak of velocity and still use the value (magnitude) from speed? if the body is moving to the west, should we denote the velocity as negative in place of the direction? (are these silly questions?) these aren't really my homework. i just sometimes ask these to myself whenever i solve problems in physics.

[theCPE]

Yeh, speed and velocity are ever so slightly different.

 

Speed being scalar velocity being a vector.

 

Google is really good, you can find a lot of amazing resources for general questions like that instead of waiting for responses here.

[swansont]

I wouldn't even modify it with an "ever so slightly." The difference between scalar and vector is an important distinction, and when you blur that (as in getting sloppy in distinguishing speed and velocity) you can get into some difficulty.

[theCPE]

Well the difference between the two in my mind is slight, and I haven't run into any difficulties yet but each to his own I suppose.

[insane_alien]

if something is going round in a circle very fast it can have a very high average speed but its average velocity will be zero. big discrepancy.

[theCPE]

Wow, this is pretty sad. I can't believe people want to argue over someone saying speed and velocity are slightly different conceptually to prove their superiority.

 

They are day one physics concepts......if those concepts are examples of huge descrepancies I don't think the forum has enough bandwidth for some of you to describe the difference between more complex and unrelated concepts from higher physics.

 

 

And btw the difference in the above example isn't HUGE. The numeric value difference might be large (X - 0) but the conceptual differene is hrm...SLIGHT. The difference of course being displacement and distance...yeh vector vs scalar.....

[swansont]

The issue is that they are day-one concepts (or even prerequisite concepts) that cause problems much, much later if they are absent. People are still wrestling with vector vs scalar issues when the teacher had hoped to be addressing physics concepts, that are more difficult to convey without a good grounding in the basics.

[Bignose]

Good gravy, CPE! swansont maybe didn't want to speak up here, but I'm going to speak up for him... in no way was swansont trying "to prove their superiority" because there is a very significant difference between vectors and scalars. My personal opinion is that swansont wasn't trying to prove anything except that getting the fundamental's right forms a much more solid foundation for future learning. The specific components of a vector transform depending upon what corrdinate system is being used. Scalars don't.

 

Consider starting with a 2-D Cartesian coordinates and let's observe a particle moving along the x-axis at 1 m/s. In this case, both the speed and the x-compnent of the velocity is 1 m/s. But, now, let's rotate the coordinate system 90 degrees. Now, the velocity is in the y-direction, but the speed is exactly the same. But the velocity is very, very different. Now, let's rotate the coordinate system 45 degrees. The speed is still 1 m/s, but now both the x and y coordinates of the velocity are 0.707 m/s. Very different indeed. In no way would I call this difference "slight".

 

This doesn't even cover if you wanted to describe the velocity in cylindrical or spherical or bipolar coordinates or any other coordinate system. But, no matter what coordinate system you use, the speed being a scalar remains the same.

 

swansont's point here is that the language of physics includes vectors, and different coordinate systems, and that knowing how they work properly is fundamental to knowing physics properly. CPE, I'd suggest you do yourself a favor and read one of the many good texts on vectors, like Schuey's Div, Grad, Curl and all that to learn just how different vectors are from scalars.

[theCPE]

I have a very good grasp of vectors and scalars...they are easy concepts...hence my point, but thanks for you concern.

 

 

I still find it amusing that there are actually people that are willing to put such energy in fighting over the fact I described the difference between speed and velocity as slight.

 

And again, if you are someone that classifies the difference between speed and velocity as a "BIG descrepancy" (direct quote from someone previously) I would really love to see you describe the difference between more complex and unrelated concepts from later courses.

 

Again, I think it really comes down to some people having a need to always put in their semantec two cents, it is after all the internet where everyone is an expert!

[swansont]

I have a very good grasp of vectors and scalars...they are easy concepts...hence my point, but thanks for you concern.

 

My experience as a physics instructor puts you in the minority in thinking they are easy concepts.

 

 

I still find it amusing that there are actually people that are willing to put such energy in fighting over the fact I described the difference between speed and velocity as slight.

 

And again, if you are someone that classifies the difference between speed and velocity as a "BIG descrepancy" (direct quote from someone previously) I would really love to see you describe the difference between more complex and unrelated concepts from later courses.

 

Again, I think it really comes down to some people having a need to always put in their semantec two cents, it is after all the internet where everyone is an expert!

 

Everone thinks they are an expert.

 

One source of problems with internet discussions occurs when people assert opinion as fact, and subjective experience as if it were objective truth.

[theCPE]

My experience as a physics instructor puts you in the minority in thinking they are easy concepts.

Are you a highschool instructor?

 

I really can't fathom vectors or scalars being considered anything but easy concepts, unless of course you are talking about the opinions of average high school students or average freshmen undergrad taking physics as an elective.

 

 

 

 

One source of problems with internet discussions occurs when people assert opinion as fact, and subjective experience as if it were objective truth.

Yes, your opinion is that vectors are a complex concept and speed and velocity are vastly different concepts.

 

My opinion is that vectors are a basic idea that if you can't grasp easily you should probably not be in the science or math field, and speed and velocity are very similiar concepts that can be mastered and understood at the same time.

 

You say I am in the minority from your experience as an instructor. I say you are in the minority, as I have yet to come across another engineer in grad school or in industry that struggled with vectors or scalars. Now, if you are also polling individuals that have no use for knowing about vectors and scalars like say bank tellers etc, then I am sure the majority of people in the world feel vectors are complex. Of people in the science and engineering fields however, I doubt that is the case.

 

Neither of these view points is an objective truth, they are of course subjective opinions.

 

But hey, everyone has an opinion.

[swansont]

Are you a highschool instructor?

 

I really can't fathom vectors or scalars being considered anything but easy concepts, unless of course you are talking about the opinions of average high school students or average freshmen undergrad taking physics as an elective.

 

No, but it was at a similar level (navy, enlisted personnel, most right out of high school). The majority of people who take physics (or post here) are probably not physics majors, and the majority of students in many places do not take physics at all.

 

Within the sphere of physics, vectors are simple concepts, only because of a whole bunch of stuff that's harder.

 

 

Yes, your opinion is that vectors are a complex concept and speed and velocity are vastly different concepts.

 

My opinion is that vectors are a basic idea that if you can't grasp easily you should probably not be in the science or math field, and speed and velocity are very similiar concepts that can be mastered and understood at the same time.

 

You say I am in the minority from your experience as an instructor. I say you are in the minority, as I have yet to come across another engineer in grad school or in industry that struggled with vectors or scalars. Now, if you are also polling individuals that have no use for knowing about vectors and scalars like say bank tellers etc, then I am sure the majority of people in the world feel vectors are complex. Of people in the science and engineering fields however, I doubt that is the case.

 

Neither of these view points is an objective truth, they are of course subjective opinions.

 

But hey, everyone has an opinion.

 

As you note, your sampling was limited to engineers in grad school and industry, which is not representative.

 

 

If the OP had been in the context of something more advanced than the first part of first-semester physics, then your statement probably would not have been noticed, since the responce would have been along the lines of "How did you get this far if you don't know the simple difference between a scalar and a vector?"

[theCPE]

Anyone seriously considering physics, science, or some technical field of study I don't think can consider vectors complex if they expect success. I figured anyone with the iniative to seek aditional help on the topic was serious and thus why I referred to speed and velocity as very similar concepts.

 

And again, it was an opinion, just like yours that they are very different.

 

I was shocked at the eagerness for some to contradict and fight such a harmless comment.

[hotcommodity]

I can understand scalars and vectors being simple concepts if you're simply considering a value and a direction, respectively. But its been my experience that they require more thought when you start considering projections, bases, norms, etc. I wouldnt think that anyone here is trying to pick a fight, but as a physics major I've noted the importance of precision, which is what I believe swansont was getting at.

[Bignose]

Well, CPE, I think that you started this with your comment "to prove their superiority". At least for me, that's why I felt the need to reply again.

 

Because, there is a fundamental difference between speed and velocity, and if you don't have any problems distinguishing them that is great. But, the average physics student does, and emphasizing that difference and making sure the difference is clear right from the start builds a strong foundation upon which to build the rest of the physics knowledge.

 

The language of physics is meant to be exact. If you say "speed" then you mean one thing that is different than saying "velocity." These words are defined exactly so that their meaning is clear every time you use them. This is the preciseness that hotcommodity is talking about.

 

It has nothing to do with ego, or "proving one's superiority". It has everything to do with being clear and using the words as intended and not blurring their definitions for someone who is not as familiar with their uses as you or I.

 

It is fine that it is your opinion that "speed" and "velocity" aren't different, and it is fine that many of the rest of us think that they are significantly different. And many of us probably are not going to budge in our opinions that they are significantly different. I don't think we, and I know myself, that we aren't "eager" for a fight, it is just that we are trying to be as clear as possible. Insane_alien's example was great about a particle zipping around a circle quickly. It shows very clearly the difference between speed and velocity, and many of us think that that is a very important distinction to make. If that is "eagerness" for a fight, we then I guess that's that. But, I (and I think the rest) are just trying to make sure that any beginners or new students to physics makes sure that they understand the very fundamental difference between speed and velocity. That's all.

[theCPE]

It is fine that it is your opinion that "speed" and "velocity" aren't different,

Wooooh wooh wooh. I never said speed and velocity aren't different, so don't say I did. I have from my first post said they are different but similiar concepts that are simple to understand.

 

Try to at least be honest and truthful when you paraphrase people.

 

 

I don't think we, and I know myself, that we aren't "eager" for a fight, it is just that we are trying to be as clear as possible.

I don't think people are eager to fight, but instead eager to provide their symantec two cents just to see text they wrote on the page:)

 

But, I (and I think the rest) are just trying to make sure that any beginners or new students to physics makes sure that they understand the very fundamental difference between speed and velocity. That's all.

 

As am I. Hence why I told the guy that speed and velocity are different, albiet slightly, because they are related concepts and that he should try google for some good resources.....

 

Since then actually it appears you have spent the entiriety of your energy on arguing about my opinion on how large the difference between the two instead of helping the poster who had questions pertaining to speed and velocity, so how are you making sure beginners understand fundamental concepts by arguing with me and misquoting me about my opinion on how simple and slightly different speed and velocity are?