What sort of can would roll the fastest?

2
0

Summary:

What sort of canned food would roll the fastest (assuming the ramp remained constant and the can couldn't be altered)?

Main Question or Discussion Point

Hello, I'm new here so apologies if this is in the wrong place! I was wondering, hypothetically, what sort of canned food would roll the fastest (assuming the ramp remained constant and the can couldn't be altered)?

I've been looking this up and I know a solid can would roll faster than an empty one. So does that mean a can with more solid, denser food, like Spam, would roll faster than one with thin soup? But I found this lab about a Soup Can Race that says a soup of chicken broth should beat other, thicker soups. I also saw this YouTube video about viscosity which says soups with things inside, like noodles, would roll slower because of friction caused by all the material swirling around.

I don't really have a good understand of moment of inertia and how the movement of substance inside the can affects the can's rolling speed. Any help would be appreciated!
 

Answers and Replies

tnich
Homework Helper
1,048
336
Generally, the less turbulent motion within the can, the faster it will roll. So a can full of cranberry sauce should roll faster than a can full of chicken broth, and the chicken broth should move faster than a can of chicken noodle soup. Things moving inside the can do rub against each other and against the can itself, converting energy into heat. So the kinetic energy of the can, and hence its speed, is reduced. The same goes for liquid swirling in the can, though it probably will not convert as much kinetic energy to heat.
 
2
0
Generally, the less turbulent motion within the can, the faster it will roll. So a can full of cranberry sauce should roll faster than a can full of chicken broth, and the chicken broth should move faster than a can of chicken noodle soup. Things moving inside the can do rub against each other and against the can itself, converting energy into heat. So the kinetic energy of the can, and hence its speed, is reduced. The same goes for liquid swirling in the can, though it probably will not convert as much kinetic energy to heat.
Oh wow, interesting! Thank you, that explains it very clearly. Does the mass factor into the can's speed? I'm assuming cans with solid material, like beans, usually have more mass, but they'd be slower because the material rubs against each other?
 
tnich
Homework Helper
1,048
336
Oh wow, interesting! Thank you, that explains it very clearly. Does the mass factor into the can's speed? I'm assuming cans with solid material, like beans, usually have more mass, but they'd be slower because the material rubs against each other?
If you use similar cans and fill them with different materials, the moment of inertia of the can itself will be the same. Assuming it has a uniform density, the moment of inertia of the food inside is proportional to its weight. If you put the two together, a denser substance inside the can will result in a higher acceleration going down the ramp, though the effect would be very slight. That is because the denser its center, the less an object resists rotation. Think of a figure skater rotating faster as she pulls her arms in toward her body.
 
Mister T
Science Advisor
Gold Member
2,384
691
Another way of looking at it is that when you have a can filled with a solid, all of the can's contents start to rotate as soon as the can starts to roll. But if you have a can filled with a liquid, all of the can's contents do not start to rotate as soon as the can starts to roll.
 
tnich
Homework Helper
1,048
336
Another way of looking at it is that when you have a can filled with a solid, all of the can's contents start to rotate as soon as the can starts to roll. But if you have a can filled with a liquid, all of the can's contents do not start to rotate as soon as the can starts to roll.
That's an interesting point. So if less mass is rolling, the moment of inertia is smaller, and the can of liquid picks up speed more quickly, at least to start. I think that effect would be very brief, though.
 
DEvens
Education Advisor
Gold Member
1,118
369
Another way of looking at it is that when you have a can filled with a solid, all of the can's contents start to rotate as soon as the can starts to roll. But if you have a can filled with a liquid, all of the can's contents do not start to rotate as soon as the can starts to roll.
Which is part of why it's difficult to spin a fresh still-in-the-shell-not-cooked egg, but if it's hard boiled and still in the shell, it spins like anything.

So which would roll fastest, a raw egg or a hard boiled egg? I'm guessing the raw one. Might be some egg rolling going on at my place tonight.
 
Mister T
Science Advisor
Gold Member
2,384
691
That's an interesting point. So if less mass is rolling, the moment of inertia is smaller, and the can of liquid picks up speed more quickly, at least to start. I think that effect would be very brief, though.
If you set a cup of liquid on a rotating platform that's speeding up, does the rotation rate of the liquid at the core ever reach the rotation rate of the cup?
 
33,579
9,315
A low viscosity fluid will start rotating slower, keeping the can faster.

I tried to get a can of superfluid helium in the supermarket but they didn't understand me. You probably want to add some insulation or perform the experiment in a vacuum, otherwise you get condensation (water ice or nitrogen/oxygen).
 
jbriggs444
Science Advisor
Homework Helper
7,866
2,773
If you set a cup of liquid on a rotating platform that's speeding up, does the rotation rate of the liquid at the core ever reach the rotation rate of the cup?
I have in mind a testbed on a long slope. Like a hypothetical 12 mile highway down from the top of Pikes Peak.

An empty can built of thick metal and an equally massive can built of thin metal filled with congealed grease should reach near-identical terminal velocities. The grease can should hit the bottom a bit early due to its head start from its lower moment of inertia.

A third can with the same mass and dimensions filled with chicken broth (and head space) should reach a slightly lower terminal velocity due to the fluid friction and dissipation of energy into turbulence and internal heat. Despite an even larger head start, it should come in dead last due to the reduced terminal velocity.

Without the head space, the broth should wind up spinning at full speed and I'd expect it come in first.
 
jim mcnamara
Mentor
3,660
1,908
https://arxiv.org/abs/1408.6654 discusses a liquid filled cylinder rolling down and inclined plane.
The authors make claims about viscosity which do not, to me, seem to agree with what has been mentioned.
Caveat - Fluid dynamics is not my area at all. However, this a great thread, IMO.
 
33,579
9,315
They study the long-term acceleration. Things can get a long head start even if the long-term acceleration is the same.

If we run this in the atmosphere then the object will attain a finite speed and more mass wins over very long distances, independent of the interior (as long as it doesn't keep dissipating energy).
 

Related Threads for: What sort of can would roll the fastest?

Replies
13
Views
2K
Replies
1
Views
2K
Replies
1
Views
436
Replies
5
Views
723
Replies
0
Views
2K
Replies
22
Views
16K
  • Last Post
Replies
5
Views
2K
  • Last Post
Replies
5
Views
7K
Top