Tuesday, November 25, 2008

General Science: I can't believe it's butter!

This week the kids learned how to make butter. It's pretty simple, really...you take some heavy cream at room temperature, put it in a jar with a marble, and shake it up until it turns into butter. The kids made observations of the contents of the jar every 3 minutes, noting when the cream changed from liquid to solid. We discussed why this happens, and how it is COMPLETELY different from what we learned last week about phase changes. The reason the cream turns into butter is NOT because it is losing heat, but rather because the tiny fat bubbles that are suspended in the cream gradually stick together until the mixture separates into butter, a solid, and buttermilk, a liquid.

Finally, we added a little salt to the butter, spread some on a baguette, and had a yummy treat! Of course, eating the bread and butter was preceded by an interesting conversation about what the threshold amount of bread is requiring a bracha. Someone in the group suggested 56 grams. (Is this true and are there other considerations besides the mass? I don't know, and I'd appreciate more information from someone who does.) In any case, we measured a slice of bread on the triple beam balance and found it weighed about 10 grams less. Most kids preferred the baguette, and while we didn't take measurements, I would guess that they consumed at least 56 grams.

Three cheers for torah u'mada!

Physics: Good Vibrations

This week we started a new topic: SOUND. We talked about what a sound is and experimented with sounds produced by different materials. The kids made oboe-like straws, plucked rubber bands of different widths and lengths across shoe boxes, bounced wooden sticks off the sides of tables, and struck water-filled glass jars, noting in each case which changes affected the pitch. Finally, the kids used their observations to created their own instruments, and then we had a concert!

Wednesday, November 19, 2008

General Science: Vanishing ice cubes

This week we started talking about states of matter and observed and documented temperature changes in ice cubes as we heated them in a pot on the stove. At first the kids started off working in pairs, but ran into several problems. I gave each group 2-3 ice cubes and they went from solid to gas in under 3 minutes (the ice, not the kids), plus keeping track of the time and taking measurements was very difficult to do consistently with just 2 people. So while we were able to see that the temperature went up, we didn't learn much about what happened along the way. As a group we brainstormed how to redesign the experiment so that we could see whether the temperature goes up consistently or not. We decided to a)start with more ice, so that is would take longer to melt and b) work as one big group with each kid being responsible for 1 measurement. This worked great and after conducting the experiment, the kids graphed their data and noted some interesting, even surprising results. The temperature did go up, but not in a straight line. Along the way, there were periods of time where the temperature didn't change much at all. Even more surprising was one example of the temperature going down. Were these results because of mistakes we made, or do they reveal something cool about phases changes.....stay tuned!

Physics: Stopping on a dime

This week the kids used their physics skills to solve an engineering problem: What is a safe distance between an out-of-bounds line on a basket ball court and a wall or other obstruction? To figure this out the kids carried out several experiments. First they measured their reactions times: Kids worked in pairs and took turns trying to catch a falling meter stick. The point on the stick where the person caught it was used to calculate the subject's reaction time.* Then everyone in the group was timed running a 25 meter course in addition to measuring the distance each runner overshot the finish line.

After an involved discussion about the challenges of safe design in general, the kids decided that it makes the most sense to consider the slowest reaction time, the fastest speed, and the longest overshoot in order to come up with the safest estimate for the distance between the out-of-bounds line and other obstructions. Next week we will do the final calculations, i.e. multiplying the fastest speed by the slowest reaction time to get the distance a runner might travel while reacting and added it to the overshoot distance (the distance one travels while physically trying to stop - people don't usually stop on a dime, particularly not during a competitive sport like basketball.)

* I just gave the kids a chart of distance fallen vs time, but as you physics geeks out there know, you get this by solving for t = the square root of (2d/9.8). Basically if you know how far an object has fallen, and you know the acceleration of gravity ( 9.8 meters/seconds squared), you can figure out the travel time, which for our purposes indicated the reaction time. The reason we didn't just time it, is that reactions time are really short, difficult to measure, and these measurements would themselves be unfairly

Wednesday, November 12, 2008

General Science: The Right Stuff

This week the kids had to design a spacesuit that could withstand the intensely high temperatures one might find on Venus. Lacking the funding to actually travel to Venus and not wanting to violate the Helsinki Declaration (ethical principles for research on human subjects), we used shlukim instead of people, and boiling water instead of Venus. The kids decorated their icy subjects, and then dressed them in spacesuits they designed from a range of materials including aluminum foil, paper towels, and inflated ziploc bags. To make it a proper experiment, we first tested a control shluk, a subject not wearing a spacesuit. The subjects were then placed in boiling water for 1 minute. Afterward, the kids opened up each shluk and measured the volume of liquid to see which one melted the least. While many an alien/astronaut costume is made out of aluminum foil, the clear winner in this experiment was the inflated ziploc bag.

Physics: SPEED

This week the kids worked in teams calculating the speeds of different test subjects doing everything from running to ripsticking (can't I just say skateboarding?!). First the kids measured out a course, then they timed the subjects completing the course, and finally they calculated all the speeds. Afterward we reviewed the data and noticed some interesting results. Turns out a lot of kids hop faster than they ripstick. So when your kid tells you he/she MUST have a ripstick in order to get to school on time, you just tell them (with confidence) how you used to hop to school, uphill both ways, and it worked just fine!