Slow Roller Physics Project Help

[luvrsofsunydale]

**URGENT** "Slow Roller" Physics Project Help

Hi,

I'm new in the forum and my project partner and I need some help/ideas regarding what will yield us the best project in class.

The object is to create a "slow roller", AKA a device that will roll down the length of 1 meter at a 13 degree incline at the slowest speed. The rules and resrictions on matirials and such can be found here:

http://www.mcps.k12.md.us/schools/woottonhs/academics/science/finalfront/slowroll2005.html

My teacher told us that when testing the very good slow rollers in past years the judges have had to stop timing after 5 minutes because the roller had barely moved down the meter stick at all. <--------THIS IS MY GOAL!

Now let me just say I am not asking for someone to GIVE me the answer to making the slowest roller, THAT WOULD BE CHEATING! lol. I am simply asking for some ideas to set is in the right direction because we are quite stumped right now as to how to go about making ours the SLOWEST slow roller.

Please respond as soon as possible so I can get started on this.

THank you much,

Lis Ferri <---- wow he is cute

PS: I'm in Honors Physics and in 12th grade.

 

[andrevdh]

I'am thinking something along the line of the can which rolls uphill by itself. It uses elastic energy to achieve this. The elastic is wound up before you put the can on the uphill (well you asked very politely that we must be vague).

 

[luvrsofsunydale]

thanks! you can be a LITTLE less vague

thanks a lot. we are not aloud to use cans but mayde we could make something out of wood or cardboard that would work like the can. so are you saying the elastics are wound up inside the can and when you let them go they spin the oppisite direction and it propells the can up to ramp instead of down?

any more ideas and suggestions are VERY appreciated!

~Lis

 

[Danger]

Perhaps a clamping force applied to sides of the stick would be helpful.

 

[andrevdh]

Yes luvrsofsunydale, you are thinking along the right lines. The elastic has a mass hanging from it. When the tube is rolled the elastic is wound up (due to the inertia of the mass).

 

[Andre]

Must it be round? Maybe Think of the highest possible moment of inertia (which resists change in spinning the most) and the smallest possible diameter for the roller itself.

 

[Andre]

To amplify that, there was a physical quiz question: you have two cilinders with the same dimensions. Both have the same weight too. however, one is solid wood, the other hollow but made of steel. Which one will be at the end of the slope first? And the correct answer was not "both simulateously".

 

[andrevdh]

Sorry, my suggestion does not comply to the rule "Every part of the device must have the same rotational motion" since the mass hanging from the elastic will not share the rotational motion.

 

[Danger]

Well, that part about 'the same rotational motion' messed up my idea of counter-rotating masses. Back to clamping force for me. I was thinking of something like this:

I========I

where the '=' signs indicate a tube. The 'I's would be disks held together by an elastic passing through the tube, which would hug the sides of the ruler (not shown).

By the bye, how bloody many Andres are there around here, anyhow?

 

[andrevdh]

Another idea, use air friction to slow the rolling motion down. Mount balsa wings on the ends of the axle. The wings should be V-shaped with the wider side outwards. Cut the central portion of the wings out and glue gauzy material in the cutouts. When the material moves through the air it creates lots of little air streams with resulting eddies and therefore large resistance to motion. Even better would be if one could build a sort of drum structure with the material stuck radially between the two discs, this would force the air to move through the material and not around it.

Danger, your idea is'nt allowed either since it needs to roll down for at least 80 centimeters

 

[Danger]

Sorry, I should have specified that the tension on the elastic be set so that the resistance of the disks is just very slightly less than the gravity force. (Like riding the brakes on a coasting car just enough to let it creep down a hill.) Good idea about the vanes.

 

[andrevdh]

Another approach is to design the device such that the it's centre of mass shifts as it rolls (how to achieve this is the real problem - curved cutouts in which dowels can move about?) so that the horizontal offset
$$\Delta x$$
of the com is always just in front of the contact point thereby simultating the effect as if the roller is on a less steeper incline (it is the torque of the weight of the object that causes it to roll down the incline). If you do decide to go the vanes/wings way you need to inquire about the condition of draughts when the competition is done, since a tail wind will actually drive it down the incline.

 

[andrevdh]

Keep the axle that rests on the ruler as thin as possible (a toothpick) since the distance covered along the ruler is the circumference of the axle for each rotation of the structuure. Danger's idea can be implemented by glueing material to the insides of the discs that rotate past the ruler. This material then rubs against the sides of the ruler as the discs rotate past it.

 

[luvrsofsunydale]

thank you all so much!

Thanks all soo much!

My project partner decided it would be "unethical" to look on here before we made a rough draft ourselves. Really he just hates the idea of not being able to figure something out on his own :tongue: ! LOL! Well yesterday we showed the teacher our rough draft, now we have to make it BETTER. So i decided to look and see the responses here. We basically came up with the same thing most of you did, small axle big side circumfrences, wings/fans etc. We've got it down to about 26-28 seconds consistantly. I will take a picture and give better explination of what we actaully have made so far later, but as far as improvments go I think we may try to incorparate the idea of the drum brake type thing. and make an even smaller axle than we have now with bigger wings. I kinda love :!) the idea about gauzey stuff on the wings but I am trying to ponder how to do that with only the given matirial. woulde finely shreded cardboard or tissue paper sufice or is it not worth it?

Keep those ideas comming, its all very helpful!

Thanks again,
Luvrs