Water and M&Ms in Microgravity

[FalTorPan]

Earlier this week I attended a lecture conducted by STS-123 astronaut Gregory Johnson. One of the stories he recounted concerned the astronauts playing with their food. As you would expect, a mass of water in microgravity tends to assume a spherical form. During one of their meals, one of the astronauts decided to throw an M&M at a "water ball" of approximately two centimeters in diameter. An expectation was that it might separate into multiple, smaller spheres. In their "experiment" the astronauts found that the water ball actually absorbed the M&M. Greg Johnson shared a photo of that water ball with three absorbed M&Ms. One appeared to be near the center of the ball, and the other two appeared to be just below the surface. None appeared to be "above" or "on" the surface of the ball.

Thoughts? Observations? Is this behavior what you might expect to see?

 

[All Seeing Eye]

I think it depends how hard you throw the M&M. If they don't throw it hard enough the water will slow the M&M down to a full stop and the M&M will be caught in the bubble. I mean there's no gravity to pull the M&M down through the water so it will just be carried in the bubble. I think if they throw it hard enough it would split the bubble like they expected.

 

[Bonzo the Fifth]

Yeah, if I'm not mistaken, the M&M would have to be thrown with enough force to overcome the water's surface tension, which I believe is the reason it becomes a sphere to begin with.

Think of it this way. If you have a bowl of water and just plink a M&M into it, it might splash a little, but effectively do nothing. Throw it harder, and you might displace a little water in the process... chuck it in at a significant fraction of the speed of light and you'll displace (likely vaporize) the water, and cause significant collateral damage.

Same thing in space, just without the bowl... unless sufficient force is applied, the water will naturally seek to remain integrated.

 

[Tobin_Dax]

The results sound reasonable for a slow enough throw. And I suspect that they couldn't throw the M&Ms too hard and still have the aim to hit and inch-wide "water ball."

Since the water is liquid, it would absorb the M&M unless it was just drifting slowly. If the M&M was moving fast enough, it would essentially be a "through and through" shot and that would probably break the water ball apart. A fast-moving M&M could impart enough energy into the water to disrupt some of its internal cohesion. A gently-thrown M&M would penetrate the water ball, but they'd both start moving in the same direction, and the friction in the water would be enough to slow and "absorb" the M&M into the water ball. This is like firing a bullet at a thick block of wood: the bullet would penetrate the block and push it, but the bullet would slow to a stop inside the wood.

Thanks for this story, FalTorPan. I'll have to remember this.

 

[JustAFriend]

It's called Surface Tension.

Didn't they do this in Skylab back in the '70s???

 

[All Seeing Eye]

I think it's basically just common sense, anybody with half a brain lobe would know why it gets caught in the bubble.

 

[Zachary Smith]

I think it's basically just common sense, anybody with half a brain lobe would know why it gets caught in the bubble.

Cause bubbles LUV to eat M&M's!!!! (Who can blame them?)

 

[Tan Ru]

Yeah, but it depends if the said M&M's were plain or peanut. In physics you must include all the factors.