14
Photogate Timer
012-06379B
®
l
Change the mass of the glider by adding weights and repeat steps 6 through 8. Do this for at
least five different masses, recording the mass (
m
) for each set of measurements. (If you have
time, you may also want to try changing the height of the block used to tilt the track.)
Data and Calculations
Table 5.1 Data and Calculations
m
t
1
t
2
v
1
v
2
a
a
avg
F
g
d =
D =
θ
=
h =
L =
c
Calculate
θθθθθ
, the angle of incline for the air track, using the equation
θθθθθ
= tan
-1
(h/d).
d
For each set of time measurements, divide
L
by
t
1
and
t
2
to determine
v
1
and
v
2
, the velocities
of the glider as it passed through the two photogates.
e
For each set of time measurements, calculate
a,
the acceleration of the glider, using the equa-
tion
v
2
2
- v
1
2
= 2a(x
2
-x
1
) = 2aD
.
f
For each value of mass that you used, take the average of your calculated accelerations to
determine
a
avg
.
g
For each of your average accelerations, calculate the force acting on the glider along its line of
motion (
F = ma
avg
).
h
For each measured value of
F
, use the equation
F = F
g
sin
θθθθθ
to determine
F
g
.
i
Construct a graph of
F
g
versus
m,
with
m
as the independent variable (x-axis).
Analysis
Does your graph show a linear relationship between
F
g
and
m
? Does the graph go through the
origin? Is the gravitational force acting on the mass proportional to the mass? If so, the gravi-
tational force can be expressed by the equation
F
g
= mg,
where
g
is a constant. If this is the
case, measure the slope of your graph to determine the value of
g
.
g
=
Questions
c
In this experiment, it was assumed that the acceleration of the glider was constant. Was this a
reasonable assumption to make? How would you test this?
d
The equation
v
2
2
- v
1
2
= 2a(x
2
-x
1
)
was used to calculate the acceleration. Under what condi-
tions is this equation valid? Are those conditions met in this experiment? (You should be able
to find a derivation for this equation in your textbook.)
e
Could you use the relationsip
F
g
= mg
to determine the force acting between the Earth and the
Moon? Explain.
