Physics/science quesions for the DIS brains...

[Cindy B]

Ok, this is in regard to my sons science project.


He is making a model of a track. (Plastic). He is using different sizes, weights of marbles on said track, and tracking the time.

He is asking me about a "force" question... either a "g" Force or centrufigal force or even velocity question... but silly me, was inept in science.

Is there any formula out there, which would determine those things.


He just doesnt want to list which marble is the fastest, he wants to know why... why does the small marble go faster than the bigger, glass one. He wants to PROVE it.


It doesn't have to be a complex formula (this is a school science fair).. but something that he can multply/divide to get the answer.
He likes to know all the answers but I don't know how to answer him.


Thanks!

 

[Serena]

My dd could help, but she's asleep, I'm sorry.

 

[Saffron]

He just doesnt want to list which marble is the fastest, he wants to know why... why does the small marble go faster than the bigger, glass one. He wants to PROVE it.

Then let him! That's what this project is all about. It's a learning project. He should be able, through experimentation, find out why things work the way they do! That's true meaning. Don't give him the answers, see if he can figure them out on his own! Then he'll be able to explain it to others.

You know why you weren't very good in science, Cindy? Because someone gave you the formulas. Over the years, we forget those formulas and foget why, because those formulas were really meaningless to us. In working with your son, finding answers to why, finding ways to find those answers on his/your own, will create meaning and true learning.

And besides that, I forget the formulas. LOL!

 

[nativetxn]

If I am remembering my kinetics, the formula is F=ma
F=force
m=mass
a=acceleration

It's been over 20 years though, so I could be totally wrong

 

[daughter_of_amid_chaos]

I am failing physics at the moment BUT i do have some equations.

F=force
m=mass
a=acceleration
F=ma

v=velocity
R=radius
ac (centripetal acceleration)=v^2
R

I don't know if he needs momentum but:
P (momentum) = mv (mass x velocity)
If the force (f) = 0, then the Mass x Final Velocity will equal the Mass x Initial Velocity or Mvf = Mvo

Those are all the notes I have with me tonite.
I don't know if this will help.

 

[#1 Disney Fan]

Well I don't know how much I can help you, but I'll give a few tips anyway.

First of all, in reference to:

It doesn't have to be a complex formula (this is a school science fair)..

You're not going to have much of a choice. The formulas will be the formulas to solve the problem, and the complexity won't be something you can *really* control (for the most part... you can have some simplifications by making assumptions... for instance assuming that the track is frictionless).

Secondly, this is a lot more complex than it seems on the surface (I think at least, without diving too far into the formulas). You're not going to be able to solve it using just these formulas given here, for you're going to have to take into account the fact that it's on an inclined plane using trigonometric functions. (The force will have two components... and instead of being able to use F=mg, you would have F=mgsin(alpha) and F=mgsin(beta).) Here's a website that helps explain this. http://www.glenbrook.k12.il.us/gbssci/phys/Class/vectors/u3l3e.html

What grade is your son in? If this is elementary school, I might suggest a different project. High school... I'd suggest he talk to his physics teacher for help in deriving the formulas.

The hard part about this project is not rolling and timing the balls on the track he makes... it's going to be deriving and combining the formulas. *That's* the tricky part here and where most of the work lies... especially if this is for a younger grade.

Another hint... you're not going to be wanting to look for a formula to solve for F (force)... you're going to want to solve for T (time) that it takes. Yes, you'll probably use force in getting there, but the ultimate answer should be comparing the T's for the various marbles.

This isn't the same as your son's project... but here's a link to a site doing a science experiment on forces on an inclined plane. Different than your sons... but maybe the procedure that they followed will help him find some more direction.

I would also suggest doing some Google.com searches and reading through the physics sites... and then finding a physics text book or 2 or 3 and looking for references there as well.

This is as much as I can help you off the top of my head... I don't remember enough about the formulas to actually solve the problem... just maybe help steer him in the right direction a bit.

GOOD LUCK, and let us know how he's doing.

 

[Kirk]

Some food for thought!

If you drop two items from a bridge, say a one ton box full of feathers and the same kind of box with a ton of lead in it, which one hits the bottom first?

My point is there is something else going on here. Is the track flexing under the weight of the heavier marble? Does one of the marbles have a greater resistance to its movement? (Friction?) Are there corners in the track? If so, does the heavier marble rub the sides more as it goes through the track? Are the corners banked? What would happen if you use smaller marbles made of metal or larger ones made of plastic or wood? Once you figure out what is slowing one marble down, is there something you can do to speed it up? What about the material you used to make the track? Stiff of flexable? Smooth or rough? What difference would that make? Does changing the slope of the track make a difference in which is relatively faster? If you put an object at the bottom of the track which marble moves it the farthest? What if you use the other marble at the bottom, can you measure how far it's moved? Now change places and measure again. (Momentum is always conserved! M1 x V1 = M2 x V2) How reliable is the time measurement? Or are they racing side by side? What difference does that make?

IMHO you probably don't want to get to intense in formulas that cause many o' nightmare to most college freshmans. (You're supposed to be able to explain these projects.) Keep it simple! Ask the questions, form a hypothesis then test it. Show your results and explain why (or why not) they prove your hypothesis. Think about other experiments to answer anything left unexplained or to further support your conclusions. The key is NOT to try to do it at the last minute! If you have time your little one can find many people willing to listen to questions and hopefully point him in the right direction. Ask me anytime! I've judged many of these fairs up to the regional level.

Kirk (Ph.D. in Chemistry)

 

[Cindy B]

Thanks.. its a plastic track with curves. Its a kid type kit called marble maze game about several hundred pieces which can go in many pieces./configurations . His marbles are smaller larger in size, glass, plastic, etc.

He a type of kid that likes to know why... and what he can do to get an answer he wants.

This is the type of kid who proves equations
for fun... I've caught him in bed doing equations... writing I know this is true... and equations on boths sides... this is the type of kid I have in my house...

He wanted to design a roller coaster and talk about G force, so this was a compromise for him

I thought the formulas would help him, because he's a WHY kind of kid... why is this faster every time? How come the small marble is always the winner? Why does the glass one go on the sides...

He likes PROOF, and reasons... just because they do, isn't his style.

 

[browneyes]

Have you checked out askjeeves for kids? You might can get a hypothesis there that your ds will approve.