APC Physics: State Fair REHEARSAL Lab
10/03/12

Cramming your measurements and results into a small space in your lab book will result in the
loss of 20% of your points; in this AND ALL FUTURE LABS, at least 1/3 of your lab book page
should be left blank for graders’ comments. And the blank space must not be all in one place
(e.g., at the bottom of the page)

Let me know what tools you need for measuring.

Document what you did and how you did it, along with measurements (some may require a
diagram) because in general specific procedures have not been given to you.
Do not refer to pictures/diagrams in lab handouts; your lab journal should stand alone if being
read by a grader. I do not need a long story, however. Be concise, but complete.

All times below INCLUDE traveling time to the next site.

Times allotted do NOT include time for calculations; calculations can be done later.

Make sure that the lab guide is taped in your book, and make sure you follow all expectations.
There is no excuse at this point for less-than-half-page diagrams, starting lines with numbers,
using formulas with numbers first rather than symbols, etc etc

Record ALL raw data, which means when using either accelerometer, you draw a picture of the
entire apparatus showing where the bob or central BB is, NOT just your interpretation of the data.

Communication and presentation of results, data taking, accuracy, significant figure consistency,
and good physics are all important in this lab
1) Determine the length of your NORMAL WALKING pace by walking the entire length of the Bryan 4th
floor.
10 - 15 MINUTES
2) Determine the distance from the Bryan front door to the edge of the curb on the north side of Club
Blvd.
BE OBSERVANT OF TRAFFIC!
10 - 15 MINUTES
3) Determine the height of one of the smokestacks by the method you read about last night on the
Horizontal and Vertical Distance Measurements handout. 15 MINUTES
Each of your 2 angle measurements should be done at least three times (and read by your lab partner,
not you!).
4) For the swings: (15 – 20 MINUTES)
a) The swinger reaches some maximum height above the ground (or some maximum angle with the
vertical). The non-swinger measures this maximum angle of the swing with respect to the vertical.
b) The swinger must measure the following in just 2 consecutive swinging periods, in order to minimize
the change in maximum angle of the swing:
(1) at the bottom of the swing (i.e., the equilibrium position), measure the
(a) vertical acceleration in the 1st swinging period.
(b) horizontal acceleration in the 2nd swinging period
(2) at the max displacement of the swing from equilibrium, can measure any useful acceleration
with either of your accelerometers
Make sure that you have thought about the proper orientation of both accelerometers (t the bottom of
the swing) before you start this experiment!
Try to minimize the movement of the accelerometers as much as possible by bracing them against the
rope/chain of the swing.
(c) the goal in this lab is to compare the two accelerations (vertical and horizontal) measured at the
bottom of the swing with those calculated from physics force diagrams and equations. You came (or will
come) very close to calculating the vertical acceleration in the recent (or forthcoming) AP swing problem,
because you calculated the speed at the bottom of the swing, which then leads directly to the vertical
acceleration, right?
LAB A8d: HORIZONTAL AND VERTICAL DISTANCE MEASUREMENTS
10/4/00
1) DISTANCES ALONG THE GROUND: PACING
Knowing the length of your stride will allow you to determine the circumference of a ride (from which the radius
can then be calculated) or aid in determining the vertical height of the ride.
a) Determine the length of your stride: At normal pace, walk the length of the Bryan fourth floor hallway. Count
the number of steps required to travel this distance, and then use the known distance (in meters) to determine
your average distance covered per step. Show all measurements and calculations.
b) For pre-state fair practice, determine the distance from Bryan front door to the north side of the street curb at
Club and 9th. Show work below, with units. Partners should compare answers. The directly measured distance
will later be given.
2) VERTICAL DISTANCE: TRIANGULATION
The horizontal accelerometer contains a straw (for sighting) and a protractor (for angle measurement) that can
be combined with a known horizontal distance (measured, for example, by pacing) to determine the height of tall
objects. This method can be used to determine ride height at the State Fair.
Suppose that the top T of a ride is at height h above level ground and that you are at point S in the diagram
shown below.
T
h
S
i
f
F
B
d
a) The first task is to measure the angular height, i, in degrees, of the top of the ride as seen from point S.
The picture below shows how an angle  can be determined by the straw-protractor combination. In sighting
some mark at an angular height  to the ground, note that the angle  is the difference between the position
of the middle BB and the  = 0 mark on the protractor.
Soda
Straw

Central
BB
Protractor

Sight the top of the ride through the straw and have your partner read the angle of inclination (to the horizontal)
of the straw; this is done by noting the angle on the protractor at which the middle BB rests. Call this angle i.
b) Now pace off a known distance d directly toward the object whose height is to be determined. You are now
at point F. (See the diagram on the previous page.) It is important that:
(1) the ground be relatively level between S and F
and
(2) the distance d be a large fraction of the total distance from the start S to the base B of the ride.
Again sight the same point on the top of the ride through the straw and have your partner read the straw’s new
angle of inclination. This angle, f, is marked on the diagram on the previous page.
c) The height h can then be calculated from
h = observer’s height + d * sin i * sin f / sin(f - i)
d) If you can walk to the base B of the height h being measured, f = 90 and sin f = 1, and the expression
above reduces to
h = observer’s height + d * tan i
e) For pre-state fair practice, determine the height of the Bryan 4th floor dorm windows (facing Club Blvd) above
the front Bryan lawn without walking directly to the base of the dorm. Measure to the top of the windows.
Make a large diagram that shows all measurements (in symbols); a table listing all symbol measurements should
also be provided; show all calculations neatly. Label all numbers with appropriate symbols ! How many sets of
measurements should you make?
As an alternative you could measure the height of one of the smokestack towers.
LAB A8 & A9: Instructions for Use of the Vertical Accelerometer
10/08/97
The vertical accelerometer consists of a plastic tube (to be held vertically) which contains a lead bob
hanging from a spring. A rubber band is attached to the bottom of the accelerometer that goes around
the user’s wrist (so that the accelerometer isn’t lost if the state fair ride does something unexpectedly
exciting). There is a series of 4 or more red tape marks that should be equally spaced along the length
of the tube.
Qualities of a good accelerometer:
a) the spring is uniformly stretched and not deformed (e.g., kinks, uneven stretching, etc.)
b) the lead bob hangs from the center of the spring hook at the bottom of the spring (without kinks, etc.)
c) some part of the lead bob must be hanging at the level second red tape mark from the top
The accelerometer can be used to measure vertical accelerations in both the up and down directions by
noting the position of the lead bob relative to the red marks. Always record the position of the bob
relative to the marks, not a numerical value of the acceleration or the apparent weight.
if the accelerometer is upright
1st red
if the accelerometer is upside down
acceleration
experienced
apparent
weight
acceleration
experienced
(in units of
earth “g” ‘s )
(in units of
true weight, mg)
(in units of )
(in units of
earth “g” ‘s ) true weight, mg)
if bob here: 1 g down
0
2nd red
0g
1
3rd red
1 g up
2
apparent
weight
4th red
2 g up
3
5th red
3 g up
4
Using of the Horizontal Accelerometer
10/05/11
The horizontal accelerometer consists of an inverted protractor whose rim is surrounded by transparent
plastic tubing inside of which 3 metal Bbs have been placed.
Straw
BBs are
pictured
ANGLE
for constant
velocity
situation
HORIZONTAL
ACCELERATION CARD
The accelerometer should be held so that the straw is pointing in the direction of the acceleration the
long angle side of the plastic tubing is on the side away from the acceleration direction. The above
direction is correct for holding the accelerometer IF the acceleration is to the right! If the accelerometer
is held as shown in the picture above, the rightward acceleration will result in the BB’s moving to the left
side of the accelerometer. If the acceleration is circular, the base of the protractor should be pointed
toward the center of the circle; the BB’s will be on the opposite side of the protractor.
The force diagram for the BB’s is shown
at the left.

N
mg = weight of
mg the BB’s
and
N = the normal force of the plastic
tubing bottom on the BB’s
The net force in the vertical direction is zero (since there is no acceleration in the vertical direction:
Newton’s second law); therefore,
Fnet,V = N cos  - mg = mav = 0
therefore,
N cos  = mg
The net force in the horizontal direction is equal to ma ( where a is the acceleration, which we previously
agreed was to the left). This follows from Newton’s second law.
Fnet, H = N sin  = ma
Dividing the previous two equations gives
a = g tan
Grading rubric
1) Determine the length of your pace by walking the entire length of the Bryan 4th floor.
10 points
2) Determine the distance from the Bryan front door to the edge of the curb on the north side of Club
Blvd.
15 points
3) Determine the height of one of the smokestacks by the method you read about last night on the
Horizontal and Vertical Distance Measurements handout
20 points
Each of your 2 angle measurements should be done at least three times
a) The swinger reaches some maximum height above the ground (or some maximum angle with the
vertical). The non-swinger measures this maximum angle of the swing with respect to the vertical.
5 points
b) The swinger must measure the following in just 2 consecutive swinging periods, in order to minimize
the change in maximum angle of the swing:
(
40 points, 20 for each vertical and horizontal
5 points accelerometer picture
5 points correct interpretation of accelerometer picture
5 points correct theoretical prediction
5 points for explanation of correct theoretical prediction
Conclusion
5 points
Ontime
5 points