I do this lesson as an observation with the students gathered around the table. We talk about surface tension and most kids have a general idea of what it is.
I fill up a glass with water, but not all the way to the top. I ask the kids "Can this paper clip float on top of the water?" Kids usually say no. I add a little drama and try really hard to get the paper clip to float on top of the water and act really disappointed when it drops to the bottom each time. Then I "remember" how to do it the right way.
I slowly add more water to the glass and the kids watch as the water rises over the top but does not run down the side of the glass. It forms a dome. We talk about surface tension again.
I then take a paper clip (the smaller ones work really well) and hold it horizontally. I place one edge on the lip of the glass and slowly slide the paper clip onto the dome of water. I give it a slight tap and the paper clip slides across the top of the dome to the other side. The kids think its such a neat trick. We then make observations of how the paperclip is slightly indented into the surface of the water and that the surface tension is holding it up.
I then add another paperclip and we make more observations. Sometimes the paper clips bump into each other and float around the top. We keep going until I can no longer place anymore on top. I think we had 15 floating at once as our highest count.
After we discuss this demo and wrap it up, I show the kids how to use a pipette and have them practice using it so they are ready for our surface tension lab the next class. Using a pipette is a fine motor skill and takes practice so all the water doesn't gush out at once or come out in uneven large drops. I show them how to hold it with their thumb and first two fingers on the bulb end and to keep the pipette on a slight angle. You don't want to hold it perfectly horizontal because you want the water to be near the opening and reduce air bubbles. Holding it vertically doesn't give you as much control. You want to hold the pipette steadily and have good control.
One other key point is not to the have the tip of the pipette touch anything or submerge into the water. When they do the real lab, I remind them that the pipette tip should not touch the penny or any drops of water on the surface of the penny. I bring up that whenever I watch crime shows and they show some kind of testing liquid from a dropper touching the item they are testing it drives me nutty because they just contaminated the bottle they were using and its not using proper "CSI" techniques. =)
The kids then practice with different amounts of pressure and experiment on how to get a good even flow of drops of water, and to practice counting them. The kids really get into it and we see how many drops of water they can get in a row.
Using Publisher, I made a tri-fold brochure for this demonstration, here is the pdf.
I fill up a glass with water, but not all the way to the top. I ask the kids "Can this paper clip float on top of the water?" Kids usually say no. I add a little drama and try really hard to get the paper clip to float on top of the water and act really disappointed when it drops to the bottom each time. Then I "remember" how to do it the right way.
I slowly add more water to the glass and the kids watch as the water rises over the top but does not run down the side of the glass. It forms a dome. We talk about surface tension again.
I then take a paper clip (the smaller ones work really well) and hold it horizontally. I place one edge on the lip of the glass and slowly slide the paper clip onto the dome of water. I give it a slight tap and the paper clip slides across the top of the dome to the other side. The kids think its such a neat trick. We then make observations of how the paperclip is slightly indented into the surface of the water and that the surface tension is holding it up.
I then add another paperclip and we make more observations. Sometimes the paper clips bump into each other and float around the top. We keep going until I can no longer place anymore on top. I think we had 15 floating at once as our highest count.
After we discuss this demo and wrap it up, I show the kids how to use a pipette and have them practice using it so they are ready for our surface tension lab the next class. Using a pipette is a fine motor skill and takes practice so all the water doesn't gush out at once or come out in uneven large drops. I show them how to hold it with their thumb and first two fingers on the bulb end and to keep the pipette on a slight angle. You don't want to hold it perfectly horizontal because you want the water to be near the opening and reduce air bubbles. Holding it vertically doesn't give you as much control. You want to hold the pipette steadily and have good control.
One other key point is not to the have the tip of the pipette touch anything or submerge into the water. When they do the real lab, I remind them that the pipette tip should not touch the penny or any drops of water on the surface of the penny. I bring up that whenever I watch crime shows and they show some kind of testing liquid from a dropper touching the item they are testing it drives me nutty because they just contaminated the bottle they were using and its not using proper "CSI" techniques. =)
The kids then practice with different amounts of pressure and experiment on how to get a good even flow of drops of water, and to practice counting them. The kids really get into it and we see how many drops of water they can get in a row.
Using Publisher, I made a tri-fold brochure for this demonstration, here is the pdf.
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