Team Names: __________________________________________ period _____
Lab: Projectile Motion (Marble Drop) (15 points)
You have probably watched a ball roll off a table and strike the floor. Could you predict where it
will land? In this study, you will roll a ball down a ramp and determine the ball’s velocity with a
Photogate. You will use this information and your knowledge of physics to predict where the ball
will land when it hits the floor.
Materials
LabPro interface
Palm handheld
Data Pro program
Vernier Photogate
masking tape
marble
plumb bob
ramp
ring stand & clamp
meter stick
Procedure
1. Set up a low ramp made of angle molding on a table so that a ball can roll down the ramp,
across a short section of table, and off the table edge as shown above.
2. Position the Photogate so the ball rolls completely through the gate while rolling on the
horizontal table surface (but not on the ramp). Center the detection line of the gate on the
middle of the ball. Plug the Photogate into the DIG/SONIC 1 port of the LabPro interface. To
prevent accidental movement of the Photogate, use tape to secure the ringstand in place.
Connect the handheld to the LabPro using the interface cable. Firmly press in the cable ends.
3. Mark a starting position on the ramp so that you can repeatedly roll the ball from the same
place. Roll the ball down the ramp through the Photogate and off the table. Catch the ball as
soon as it leaves the table. Make sure that the ball does not strike the side of the Photogate.
Move the Photogate if necessary.
4. Measure the diameter of the ball as carefully as possible. The accuracy of the rest of the
experiment depends on this single measurement. You must know the diameter, s, in order to
calculate the velocity of the ball as it passes through the gate. You will divide this diameter
by the time interval t measured by the interface to get the ball’s velocity (v = s/t). To
successfully predict the impact point, you must have an accurate diameter measurement.
Record the diameter in your data table.
5. Turn on the handheld. To start Data Pro, tap the Data Pro icon on the Applications screen.
Choose New from the Data Pro menu or tap
to reset the program.
6. Set up the handheld and interface for the Photogate.
a. On the Main screen, tap
.
b. If the handheld displays TIME(S) in DIG/SON 1, proceed directly to Step 7. If it does not,
continue with this step to set up your sensor manually.
c. Tap
to select the DIG/SONIC 1 port.
d. Select PHOTOGATE from the list of sensors.
7. Set up the handheld and interface for Gate mode.
a. On the Setup screen, tap
.
b. Select GATE from the list.
c. Tap
to return to the Main screen.
8. Observe the reading on the Main screen. Block the Photogate with your hand; note that the
Photogate is shown as blocked (--X--) on the screen. Remove your hand and the display
should change to unblocked (--0--).
9. Adjust the Photogate elevation so the light beam hits the middle of the ball.
10.
Data Pro will measure the length of time the photogate is blocked. You can see how this
works by blocking the gate briefly with your hand.
a. On the Main screen, tap
.
b. Block the gate with your hand for about one second, and then remove your hand from the
gate.
11. Note that the screen now shows a time interval in seconds. This is the length of time that the
gate was blocked. Stop data collection by tapping
. Prepare the program to collect
another set of data by tapping
on the Graph screen.
12. Roll the ball from the mark on the ramp, through the Photogate, and catch the ball
immediately after it leaves the table. Record each time interval in the data table. Repeat Steps
10 and 11 until you get ten times that are close to each other. (Omit any wild times.) Tap
when you are done.
13. Record the average time it takes the marble to go through the Photogate.
14. Carefully measure the distance from the tabletop to the floor and record it as the table
height h in the data table. Use a plumb bob to locate the point on the floor just beneath the
point where the ball will leave the table. Mark this point with tape; it will serve as your floor
origin.
15. Knowing the vertical drop distance and acceleration,
record the time the ball will be air born.
h = 0.5gt2. Using this time and the average velocity
calculate the horizontal distance the ball will travel.
16. With tape mark the origin, the calculated impact
point and the actual impact point on the floor. Get
your instructor to observe an actual marble drop and
initial your lab. Show a calculation for your percent
error.
Trial
1
Time (s)
Ball diameter (d)
Average velocity (V = d/Ť)
plumb
bob
floor origin
Figure 2
m
m/s
2
Table height (h)
m
3
Time ball is air born t = (2h/g)^0.5
s
4
horizontal distance marble should travel (x=tV)
m
5
actual distance ball traveled
m
6
instructor initials:
7
Show a calculation for percent error:
8
9
10
average (Ť)