I Calculating the Mass of a Piston for a Spring-Based Launcher

[hmmm27]

I don't know why you'd build a contraption to throw a golf ball 10 feet when you can just walk over and drop it on the ground.

But, if you insist on a mechanical launch...

First you'd want to determine the best method of propulsion : direct spring, direct contact (it's a golf ball, just smack it with the piston), or a hybrid where the spring compresses air which launches the ball (commonly used in air rifles). Those you'd use principles of physics, maybe some rough calcs.

Or use common sense and use the spring to power a small catapult. That one - free of most of the friction that messes up the other ones - you could math away to your heart's content and build it. Once. No wasteage of lumber ; no having to go back to the store and buy a more or less powerful spring.

 

[InebriatedScientist]

In Physics we use established theories to predict and test the outcomes of experiments. In Engineering we use the collective knowledge of physical theory and empirical measurements to design and predict the outcomes of constructed devices or objects.

Information gathered by carefully controlled laboratory experiments, performed by many others, is what engineers use as the basis of the design of new creations. There's no "man on the street without any measuring tools" input there. Conflating the fact that the general populous has no readily available test equipment with scientists not knowing what they're doing so that science is useless is just argumentative nonsense.

THANK YOU.

So then, I would never know at what velocity a mid-size stone that someone threw of a cliff that you have never been to or have seen traveling. Or at what angle and where it will land?

Also, one more thing, if I did observer this, how would I find that angle? Could I use the person's hight?

 

[InebriatedScientist]

I don't know why you'd build a contraption to throw a golf ball 10 feet when you can just walk over and drop it on the ground.

But, if you insist on a mechanical launch...

First you'd want to determine the best method of propulsion : direct spring, direct contact (it's a golf ball, just smack it with the piston), or a hybrid where the spring compresses air which launches the ball (commonly used in air rifles). Those you'd use principles of physics, maybe some rough calcs.

Or use common sense and use the spring to power a small catapult. That one - free of most of the friction that messes up the other ones - you could math away to your heart's content and build it. Once. No wasteage of lumber ; no having to go back to the store and buy a more or less powerful spring.

Yes, all of this would make sense. But like you said it is just common sense. Obviously, if I wanted the ball to fly 30ft I would use a stronger compression spring. I would assume without math that the harder it compresses the further the ball is traveling.

 

[InebriatedScientist]

Oh for Heaven's sake!
" the project, I already made it. The ball flew about 20ft.."
OK. You've made a start. Now get a tape measure.
Repeat the experiment lots of times, keeping everything the same each time, and measuring "..about 20ft.." each time.
Take an average, now you actually know something - that with certain parameters your spring/cylinder will propel you ball X ft.
So the X ft is your starting point and you actually have a real (approximate) measure of something.
Now do it with your launcher pointing up at angles of 30/40/50/60/70 and measure x30, x40 etc.
You will have to work the physics backasswards from there with lots of assumptions
until you come out with figures that approximate the real life situation.

It isn't the best way to do physics, but its sort of a way of doing physics.
But you cannot avoid mathematics if you want a meaningful result.

Mac

Ok good, thank you. That is what I wanted people to tell me. So then YES we do assume stuff until we get it right. That means this is all trial and error. So then, why am I doing math instead of just trial and error with intuitive reasoning?

 

[berkeman]

I am not using caps to yell at you

Thank you. I appreciate that you have stopped using all caps.

When you play golf, do you also do that? do you pull out the rangefinder pull out your phone?

I acually use to play golf when I was younger. Too boring for me now. But back then and even now for professional golfers, you are allowed to use maps of the course that show distances. No cell phone apps allowed or needed.

Hey, PM me if you want to talk about this on a more personal level. Like I said above, I went through something similar early in undergrad, and found a really good way to get through it. Click on my avatar and click on Start a Conversation to start a PM thread with me.

 

[hmmm27]

Yes, all of this would make sense. But like you said it is just common sense. Obviously, if I wanted the ball to fly 30ft I would use a stronger compression spring. I would assume without math that the harder it compresses the further the ball is traveling.

The "neat" thing is that you could design it, then build it without having to resort to rebuilding it a bunch of times to get it right. Not terribly important with something that nobody told you to use math for in the first place, but consider that almost every step of this conversation - the keyboard, all the electrical signals, etc. involved not only just the principles of physics, but actually exercising the formulas.

Here's a thread you might want to weigh in on.

 

[gneill]

So then, I would never know at what velocity a mid-size stone that someone threw of a cliff that you have never been to or have seen traveling. Or at what angle and where it will land?

No, why do you think that you would? Without any empirical data you'd be at a loss except to perhaps predict the possible range of outcomes (based upon collected knowledge of the possible speed of launch of a "mid size" projectile by a human, and maybe a Google search result of the height of the given cliff). Physics doesn't magically produce results based on no data. Why would you expect it to?

You seem to be obsessed about the idea that the average occurrence is not precisely measured, so that physics can know nothing about average occurrences. That is not the case. Scenarios can be staged and the data obtained to whatever precision is desired. Yes, these are laboratory scenarios, but do you seriously expect nature to behave differently in and out of the lab?

Also, one more thing, if I did observer this, how would I find that angle? Could I use the person's hight?

What exactly did you observe, and what information were you able to reliably collect? The person's height might play a role, but you need a lot more information about the scenario to build a model that can be analyzed with precision. You might be able to infer some general estimates about the person's height based upon the observed results, but the uncertainty in the results will depend upon the error range of the given data. You can do much better in a lab setup where measurements can be accurately recorded.

Just because you cannot model a random incident without specific information does not mean that you cannot engineer a specific scenario, and build to spec with reliable data on materials and physics.

Just because a random scenario is not in a lab does not mean that you cannot analyze the given data in a scientifically appropriate way. The results will have an error range commensurate with the error range in the collected data.

 

[InebriatedScientist]

No, why do you think that you would? Without any empirical data you'd be at a loss except to perhaps predict the possible range of outcomes (based upon collected knowledge of the possible speed of launch of a "mid size" projectile by a human, and maybe a Google search result of the height of the given cliff). Physics doesn't magically produce results based on no data. Why would you expect it to?

You seem to be obsessed about the idea that the average occurrence is not precisely measured, so that physics can know nothing about average occurrences. That is not the case. Scenarios can be staged and the data obtained to whatever precision is desired. Yes, these are laboratory scenarios, but do you seriously expect nature to behave differently in and out of the lab?

What exactly did you observe, and what information were you able to reliably collect? The person's height might play a role, but you need a lot more information about the scenario to build a model that can be analyzed with precision. You might be able to infer some general estimates about the person's height based upon the observed results, but the uncertainty in the results will depend upon the error range of the given data. You can do much better in a lab setup where measurements can be accurately recorded.

Just because you cannot model a random incident without specific information does not mean that you cannot engineer a specific scenario, and build to spec with reliable data on materials and physics.

Just because a random scenario is not in a lab does not mean that you cannot analyze the given data in a scientifically appropriate way. The results will have an error range commensurate with the error range in the collected data.

What I was saying in regards what I observed was that a person was throwing a mid-size stone, now the way they threw it was from their hip. However, I don't exactly know at what angle. I was curious to know, If I asked the high of the person, and let us say they said they were 5.8ft Could I figure out the angle? Or is there still not enough data? I would assume that there was still not enough data.

Right. The reason I was hung up on it was that I imagined myself in the woods. Now I am trying to survive. I decided to engineer a bow. Now I am trapped on an island with the woods. I don't have a ruler or a way to measure anything. I would just assume and continue with it.

Anyway, I was just not sure if I should make the launcher to the best of my ability and then fine tune it with physics. Or use physics first to engineer it. The thing is, you don't need physics to engineer a bow or a projectile launcher. Just intuitive reasoning. I guess I thought that physics could be precise with everything. I thought that I could get good enough to be able to predict some things. Like let us say that someone is shooting with a slingshot at me, I thought that maybe I would able to estimate how far they could shoot it so I can avoid it.
So my other question is if there was a mid-size meteor going towards Earth how would you know exactly where it is going to hit? How would you calculate mass? PM me for this answer.

Ok, I am done speaking about this, I have gone WAY off topic. We can talk about this in some other thread.

 

[fresh_42]

Ok, I am done speaking about this, I have gone WAY off topic. We can talk about this in some other thread.

Time to close this. There have been way too many "you's" for a scientific discussion anyway.