We tried out a new science experiment today from our favorite science guy - Steve Spangler (www.stevespanglerscience.com). He's also the one who has a whole lesson for kids using the super-fun jelly marbles! Today, though, we learned a little more about surface tension when we made a "gravity defying handkerchief" hold the water in an upside down glass.
First, we put a handkerchief over the top of a glass (it has to be a glass with a round rim) and tucked it down in the center. Then, we poured some water into the glass through the handkerchief. Some of the kids were amazed that the water went through the handkerchief, so we talked about how there are tiny holes between the threads of the handkerchief that let the water go through into the glass.
First, we put a handkerchief over the top of a glass (it has to be a glass with a round rim) and tucked it down in the center. Then, we poured some water into the glass through the handkerchief. Some of the kids were amazed that the water went through the handkerchief, so we talked about how there are tiny holes between the threads of the handkerchief that let the water go through into the glass.
The next step was to slowly pull the handkerchief down to tightly cover the top of the glass. Then, I put my hand over the top of the glass, while tipping it upside down with the other.
Once it is inverted, you can remove your bottom hand, and the water will stay in the glass!
Straight from Steve Spangler himself, here is "how it works":
"Most people predict that the water will leak through the holes in the handkerchief because the water leaked through the holes as it was poured into the glass. The holes in the handkerchief literally disappeared when the cloth was stretched tightly across the mouth of the glass. This action allowed the water molecules to bond to other water molecules, creating what is called surface tension. The water stays in the glass even though there are tiny holes in the handkerchief because the molecules of water are joined together to form a thin membrane between each opening in the cloth. Be careful not to tip the glass too much because you'll break the surface tension and surprise everyone with a gush of
water!"
Now, the words I used with the preschool set were a little more like this:
"When we pulled the handkerchief tight and turned it upside down, the water held itself together on the other side of the handkerchief. That's called 'surface tension,' just like when we talked about how bubbles can hold together."
Of course, having a room full of curious kiddos, we had to test out the last part, too...what happens if you break that surface tension? So, they each got to take their turn poking at the bottom of the overturned glass to see if they could break the surface tension. They got a little bonus lesson on force when we saw that some could poke hard and fast enough to make the water leak out, and some couldn't.
"Most people predict that the water will leak through the holes in the handkerchief because the water leaked through the holes as it was poured into the glass. The holes in the handkerchief literally disappeared when the cloth was stretched tightly across the mouth of the glass. This action allowed the water molecules to bond to other water molecules, creating what is called surface tension. The water stays in the glass even though there are tiny holes in the handkerchief because the molecules of water are joined together to form a thin membrane between each opening in the cloth. Be careful not to tip the glass too much because you'll break the surface tension and surprise everyone with a gush of
water!"
Now, the words I used with the preschool set were a little more like this:
"When we pulled the handkerchief tight and turned it upside down, the water held itself together on the other side of the handkerchief. That's called 'surface tension,' just like when we talked about how bubbles can hold together."
Of course, having a room full of curious kiddos, we had to test out the last part, too...what happens if you break that surface tension? So, they each got to take their turn poking at the bottom of the overturned glass to see if they could break the surface tension. They got a little bonus lesson on force when we saw that some could poke hard and fast enough to make the water leak out, and some couldn't.
I'm pretty sure that was their favorite part. :)
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