Date: Sun, 17 Oct 2010 12:24:53

Author: Daniel Kaplan

Subject: Demo to show that horizontal velocity unaffected by vertical acceleration in projectile

Post:

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I am looking for suggestions about how to refine this demo. It is a studen=
t-run demo in small groups. The demo needs to last no more than ~ 4 minutes=
. (See below about why 4 min.)

I tried to create a hands-on demo that would allow students to realize that=
the accelerated motion in one direction will not change the constant veloc=
ity motion in the other.

I set up a board with a spring scale that I used as a shooter. With the bo=
ard flat on the table, the students first shoot a small billiard ball throu=
gh two photogates at either end of the board and determine an average time =
for motion across the board. They can easily do 5 runs in ~1.5 minutes. T=
hen they prop up one side of the board and determine where the ball will ro=
ll off the edge of the board. It is about 15 cm down from the top edge of =
the board. They then reposition the second photogate and make 5 of these r=
uns. I was hoping to get the same average time from when the board is flat=
.

Many of the groups got fairly good data, but often the average time for the=
curved path was greater than when the board was flat. I would appreciate =
any suggestions. Has anyone done a similar demo with good results?

------------------------
(Why such short time to do this:)
This was part of an "exploratorium" (I got this idea years ago from a book =
by George
Amann). This is what I call a special lab that I use to start new units. S=
tudents are in groups of 3-5 students. It consists of 5 hands-on demos. E=
very 5 minutes a bell rings and the students move from station to station, =
read instructions, declare their predictions, and then do a quick measureme=
nt. For example, one of the stations for this unit was the dropper-launche=
r. Much more fun to have the students run the demos themselves in small gr=
oups. So the self-run demos must run about 4 minutes. We discuss this the=
next day in class and then I return to it when the class lessons get to th=
e appropriate points.


Daniel Kaplan
Physics Teacher
Matawan Regional High School, Aberdeen NJ


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I am lo=
oking for suggestions about how to refine this demo. It is a student-=
run demo in small groups. The demo needs to last no more than ~ 4 minutes. =
(See below about why 4 min.)
=

I tried to create a hands=
-on demo that would allow students to realize that the accelerate=
d motion in one direction will not change the constant veloc=
ity motion in the other.

I set up a board with a s=
pring scale that I used as a shooter. With the board flat on the=
table, the students first shoot a small billiard ball through two photogat=
es at either end of the board and determine an average
time for motion across the board. They can easily do 5 runs in ~1.5 =
minutes. Then they prop up one side of the board and determine where =
the ball will roll off the edge of the board. It is about 15 cm =
down from the top edge of the board. They then reposition
the second photogate and make 5 of these runs. I was hoping to get t=
he same average time from when the board is flat.

Many of the groups got fa=
irly good data, but often the average time for the curved path was gre=
ater than when the board was flat. I would appreciate any suggestions=
. Has anyone done a similar demo with good results?

------------------------<=
/font>

(Why su=
ch short time to do this:)
This wa=
s part of an "exploratorium" (I got this idea years ago from=
a book by George

Amann). This is what I call a special lab that I use to start new unit=
s. Students are in groups of 3-5 students. It consists of =
5 hands-on demos. Every 5 minutes a bell rings and the students =
move from station to station, read instructions, declare their
predictions, and then do a quick measurement. For example, one =
of the stations for this unit was the dropper-launcher. Much mor=
e fun to have the students run the demos themselves in small groups.&n=
bsp; So the self-run demos must run about 4 minutes. We discuss
this the next day in class and then I return to it when the class lessons =
get to the appropriate points.



Daniel Kaplan
Physics Teacher
Matawan Regional High School, Aberdee=
n NJ





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