This was a weekend of scientific experiement and observation (as well as other forms of procrastination) for me. On Saturday morning as I searched for a sugary snack to eat while I tried to get some homework done before going shopping for prom dresses, I found a can of "all natural" 7UP in my fridge. When I poured it in my glass, I found that streams of bubbles were coming from the same points on the bottom no matter what I did to the glass (no, I didn't turn it upside down). I then hypothesized that there were small irregularities in those spots, as I remeber from Chem that bubbles form on irregular spots, at least when water boils. So I found a glass that my dad had dinked up the bottom by stirring liquid with a spoon and poured the other half of the can in, and found a noticable column of bubbles coming from the center with all the dinks. I have support!!!!! And this was before I really even got into my homework at all. But I know, that's Chem. Here's the simple but funny Physics encounter of the weekend. As my mom and I got home today (Sunday) and were unloading the car of our few purchases and other stuff, my mom brought up the cups of water we had been drinking. To make things easier, my mom stacked two of the cups one inside the other. She then forgot that there were two cups and took hold of the top of the top cup. Normally they would stay together because the static friction force on the two surfaces of the cups was enough to hold up the bottom cup. However, in this case, we did not drink all the water. Therefore, the weight (mg down) of the bottom cup plus the weight of the water was enough to overcome the maximum static friction force dictated by the coefficient of static friction of the cups, creating a net force pointing down. Thus, the cup slipped off, hitting the wood floor of our house with acceleration -9/8 m/s^2 (or g), not leaving a dink but resulting in a large puddle of water on our nice wood floor that had to be wiped up before it hurt the finish. The water splashed out of the cup, obeying the law of conservation of momentum, at least at first, giving the many water droplets large velocities in the same general direction to account for the large velocity and mass of the dropped cup. Thus with these large velocities, the puddle was large as well, for many dropplets flew far away. But no harm done, plus I got to explain to my mom the Physics involved. I felt smart. :-)
1 comment:
The fact that a bubble starts at one point rather than another could be a physics problem too...
When you make a bubble, it has a spherical surface to it, and the surface has a high energy. If a bubble forms in the middle of the 7UP, a whole new sphere of surface as formed for even the most tiny bubble. You have a tiny little ball of gas with a relatively big surface area. On the other hand, it could form at the edge. Rather than make completely new surface when the bubble forms, the 'bubble-7UP' surface partly replaces the existing 'cup-7UP' surface. So you're producing less new high-energy surface, and this is easier. It works even better for a rough surface or a dimple, because you are getting rid of loads of the cup-7UP surface for every little bit you grow the bubble, so that's the best place for bubbles to form.
Once the bubble has formed, then it can grow and then ratio of surface to volume goes down until it happily drifts off into the 7UP and floats up to the surface.
I hope your mum responded well to your satisfaction that dropping the cups conserved momentum - my family would just tell me to help clear up instead!
Post a Comment