7/30/2019 : IMPORTANT INSTRUCTOR NOTES

1/2

IMPORTANT INSTRUCTOR NOTES:

1. The experiments here are based on ones I have done. There are other experiments thatcan be done with the Pasco Projectile Launcher. If you have a favorite, send me a copy

and Ill see about incorporating it into this module.

2. The BASIC experiment here is really one in experimental design and empirical data

analysis. The way I do the experiment is to use one full lab period and a portion of a

second.a) In the first lab I break the lab up into teams (3-4 people per team) and give

each a launcher that has a base (see the module graphics). I show how to

load a ball and how to cock and fire the gun. I also show them how to

change and read the angle. After that, I simply say: Find out as much asyou can about your gun. There will be a contest next week where you will

have to hit a target, placed on the floor, where the distance from a fixed

mark (behind which you must place the gun) will be given. There will be

a fairly short time limit in which you must setup and fire. Bonus points (inthe class) will be awarded the winners. Collect as much (or little) data as

you want and then organize it for easy retrieval during the contest. Theythen take their launchers to areas in the building where they can fire the

guns (maximum range about 7 meters). They also have a metric tape

measure.b) I dont tell them how big the target will be or any other details.

c) The next week I run two contests. I make up a fairly large target with an

inner and outer scoring circle (about 20 and 40 cm in diameters). Each

team gets a different distance (5-7 meters). They have 90 seconds to setupand shoot AND all members of the team MUST stay behind the line from

which the distance is measured. Any team that hits within the larger circlegets some points, but the team hitting nearest the center gets the mainprize.

d) I then run a second contest. This time I place a chair very close and in

front of the firing line. This is to see if they tested the high-angletrajectories. The target is placed in the 1-3 meter range.

e) The first problem students encounter is that few teams really practiced

aiming the gun and misses right/left are common. They also tend to set

the angle and THEN cock the gun, failing to check whether the cockinghas changed the angle. It is often the case that some groups have not

studied the high-angle options at alltherefore the chair is often hit!

3. The Advanced experiment really came out of desire to get the students into a

variety of SPREADSHEET analyses. Ive not done the experiment with the

Pasco launchers, but did with our older Cenco units which had an continuouslyadjustable spring tension. In the Pasco case, the spring position will uniquely

determine the initial velocity. Students do have to take the geometry into

consideration since the launch height and ending height are different and the

ranges are measured from the front of the base. If you set the air resistance to

7/30/2019 : IMPORTANT INSTRUCTOR NOTES

2/2

MAXIMUM (see OPTIONS write up below) then this will be a major factor, but

at the MINIMAL level the effect is really small. However, this is the first place

where the students can use the spreadsheet. By developing a data set for adropped ball from different heights and a theoretical equation for a falling ball

with air resistance, they should easily determine that the dependence is on v (not

v2

) and can also get a reasonable value for the coefficient. A full analysis usingthe objects geometry is not necessary. The final analysis involves firing the

gun at different angles and spring positions both with the students equation

(calculated in a spreadsheet) and live using the actual gun. Using the spreadsheetprogram, graphs that overlay the experimental and theoretical range versus angle

data (one graph for each spring position) can be generated. We did get fairly

good agreement when we did the experiment although the theoretical equation

was reasonably complex and we ignored air resistance.

INSTRUCTOR OPTIONS:

There is a hidden screen that you can use as the instructor to set three options. To access

this screen, hit Ctrl-O at the screen that offers you the choices to check the video setup orstart the program. The OPTION screen that comes up lets you set:

1) Allow the students to view a trace of the trajectories when firingthe launcher in the BASIC experiment. This makes determining the range much

easier. This is NOT very realistic so you may want to set this option to NO although

I am packaging the module with the option set to YES.

2) The second option involves the spread in values that the studentwill get for the ranges. This is determined by setting an uncertainty range in the

initial velocity as determined by the spring position. There are three options

NONE, 1% (default), and 2%. When the uncertainty is set, it is really +/- 1% aroundthe nominal valueso the spread can be up to 2%. Likewise at a setting of 2%, the

spread can be as much as 4%. With NONE, the ranges should be reproducible to high

precision.3) The last option is to set the amount of air resistance. The settings

are NONE, MINIMAL (default), MODERATE, and MAXIMUM. The default

minimal setting produces a small effect that seems consistent with the actual

equipment. The two higher settings will make the ADVANCED experiment analysesa bit easier since the effects will be more pronounced. The NONE setting will

eliminate all air resistance effects and make deriving an equation for the motion much

easier.

The option set is kept in the file options.dta that must be in the main directory.