Sticks, stones, soap, and speeding spheres

Physcial science summer 2013 began on a Monday with an overview of the syllabus. Due to potential add/drop churn, only the syllabus was covered and the course briefly introduced.

Tuesday morning the pre-assessment was given along with the SLO pre-survey. This left the measurement and the metric system yet to be covered. Tuesday afternoon I ran a variation of sticks, seconds, and stones.

I asked the students to use their hands to show me "one meter".

I recorded the results on the board, seen on the left above. I later had the students count off seconds. The actual time span was 60 seconds, their counts are on the board to the right the meter estimates.

I used the Tanita to measure mass in kilograms and had the students work out their body mass index. I wrapped up with a brief demonstration of a balance beam to determine small unknown masses.

Wednesday morning I focused on introducing mass, volume, and density. This allowed the afternoon laboratory to focus solely on the soap. In the morning I calculated the density of various cubes, although aluminum and brass had been borrowed and were missing. I was able to do steel, wood, and lead. I also showed that the wood, with a density less than one, floated.

Tina Sue measures a slab of soap.

Tina Sue and Mackleen

Rose Ann and Risenta cut their soap

Data on Kamleen's computer

Thursday morning I introduction space divided by time, speed, and velocity. I then went out and again used the solar panel walkway. After the first gap, the support pillars are very close to five meters apart. There is a slight downhill, so I was able to maintain a fairly constant speed by not swizzling and just rolling.

time (s) distance (cm)
0 0
2.42 5
5.56 10
8.45 15
11.52 20
14.5 25
17.51 30

I generated the times while riding.

The result was remarkably linear.

In the afternoon I piloted using the bowling techniques of last spring at the solar panel walkway. I also gave each student a stop watch and had them start when the ball passed Michael, stop when the ball passed them. This really did not work. All of the old problems of this system resurfaced. Timers were not starting at a common time, some forgot to stop their watch, and data was scattershot as a result. Then too, the x-axes were different. Add in that keeping the ball traveling straight was difficult, getting the ball to go 30 meters required that the slowest ball was a really fast ball, timing errors for fast balls, and large losses in speed along the route. Overall the system of simply timing the first five seconds and measuring to the seconds mark is far superior. This allows for very slow rolling. The gym porch is also a very ideal surface as we learned last term.

Shane bowls, Michael drops his fist when the ball passes the zero mark.

Photo of Dana taken by Rafael.

Michael tries his hand at bowling.

Tracy timing at 30 meters.

The ball often went off course.

Michael dropping his arms. The ball has actually passed already. Add in the timer reaction times and the fastest ball had only two marginally useable time values out of six. This approach was always a failure and still is. Set the time, then measure the distances - where was the ball at one, two three, four, five, and six seconds. The ramp is not as important as I thought. A good bowler can repeat speeds close enough that those marking where the ball was at time t can locate those positions very accurately. Then measure the distances. This also keeps the independent variable independent.
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