**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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