PRACTICUM: DYNAMICS
EQUIPMENT:
1. A level air track with pulley on one end
2. Glider with flag
3. Photogates used in gate and pulse mode
4. String
5. Film canister with hook on the lid
6. Balance
7. Bottle of lead shot (the type with tiny spheres)
PROBLEM POSED:
Before the practicum begins the teacher places a piece of paper inside a film canister. On the piece of paper is
an acceleration value between 1.0 and 2.5 m/s2. (If the practicum is done with lab groups rather than the whole
class, a different value is in each canister.) The glider with the flag is massed in front of the students and placed
on the air track. Students are informed that when the practicum is checked the air will be turned on under the
glider so that friction can be ignored. Students are then told to take the film canister and place the appropriate
amount of lead shot inside of it so the glider will have an acceleration equal to the value on the paper.
photogates
glider and flag
pulley
film canister with
hook on lid
air track
MEASUREMENTS NEEDED:
(210.0 g)
Mass of glider and flag
SAMPLE CALCULATIONS: (For this sample the acceleration value needed will be 1.8 m/s 2)
T = (mglider) a
(equation for glider)
-T + W canister = (mcanister)2a
W canister = (mcanister + mglider)a
(equation for canister)
(adding equations)
(mcanister)g = (mcanister + mglider)a
(mcanister)(9.8 N/kg) = [(.210kg) + (mcanister)]( 1.8 m/s2)
(plugging in numbers)
(mcanister)(8.0m/s2) = .210kg(1.8m/s2)
(mcanister) = .0472kg = 47.2g
ADDITIONAL COMMENTS:
When students have calculated the answer they place the empty canister on a balance and add lead shot until it
has the correct mass. They then bring the canister to the air track and hang it on the end of the string. The
photogate program is started, the glider is held stationary and the air is turned on. When the air is steady the
glider is released. The answer is checked by running the photogate program in gate and pulse mode with the
width of the flag entered in the program. This practicum generally yields answers within 2%. If the teacher
wants the answer even closer they can angle the track down slightly. The practicum can easily be done in a 45
minute class period. Depending on the ability of your students it can be run as one problem for the whole class
or given to smaller groups, with a different value for each group. The success of the group can be checked in
10 seconds if the photogates are used.
This practicum was developed by Rex Rice