PHYSIC 1401 Austin Community College Uniform Circular Motion General Physics HW An investigation of a rotating mass on a string attached to a stationary ma

PHYSIC 1401 Austin Community College Uniform Circular Motion General Physics HW An investigation of a rotating mass on a string attached to a stationary mass through a tube.https://www.youtube.com/watch?v=ZLM7PaxStS8&feature=youtu.beplease watch the video because you will need to record “time” as it’s on the experiment on the video Name______________________
Date_____________
PHYS 1401 General Physics I
Uniform Circular Motion
Equipment
Circular motion apparatus
Digital Scale
Stop watches (pink timers)
Mass set
Meter Stick
Theory
An object of mass m in uniform circular motion at constant speed v undergoes
centripetal (center-seeking) acceleration because the direction of the velocity of the mass
is changing at every instant along the path of the motion. The net centripetal force acting
on the mass according to Newton’s 2nd law provides the acceleration,
with the magnitude of the acceleration given by
where r is the radius of the circular motion of the object. Thus, the expression for
centripetal force is
The velocity for circular motion is calculated by dividing the circumference of the circle
by the period:
and the period is found by dividing the total time taken by the number of revolutions
completed.
Procedure
You should measure the mass of the casting weight and enter its value in S.I. units in
the correct location in the table. You should then add a 50 gram mass to the mass hanger
and place the entire mass hanger on the digital scale to obtain its mass. Record the mass
of the hanging mass in S.I. units in the correct location in the table. Carefully, while
holding the plexiglass tube vertically, hold the string with the mass hanger as it comes out
of the bottom of the tube. Begin to swing the casting weight in a circular motion above
your head from the top of the tube. As you pick up speed, let go of the lower (mass
hanger) string. Adjust your speed until the red bead on the string is consistently in the
center of the region between the two o-rings on the glass tube. Additionally, you want
the circular motion of the casting weight to be as level as possible and do not touch the
string or have it come in contact with you in any way.
Once you have the motion of the casting weight fairly regular, each member of the
group should time ten revolutions of the casting weight and record the group’s average
time in the correct location in the table. To do this you should begin your counting of the
revolutions with 0, 1, 2, … 10, so that you end up timing ten complete revolutions and
not just nine. This is the most sensitive measurement that you will make in the entire lab
so repeat it three times (rewind the video and time 2 more times). This ensures that you
have a consistent experimental process down. Take the median time of the grouping
recalling that the median time is the middle time when they are placed in ascending or
descending order.
Now carefully stop the casting weight by pulling on the hanging mass. Measure the
radius of circular motion by applying enough force to remove the slack from the line.
Place the red bead in between the two o-rings and measure from the center of the tube to
the fattest part of the casting weight (the break point). Record the radius in S.I. units on
the table provided. You must subtract 9mm from this radius because the center of mass of
the casting weight is 9mm inside of the break-point position. All mass acts at the center
of mass. Use this radius for your calculations. This completes the experimental procedure
for the lab. You must now complete the lab calculations and write up on the worksheet.
Uniform Circular Motion Worksheet & Data Tables
Experimental Data (remember to convert to S.I. units for calculations)
Mass of the casting weight
Mass of the hanging mass
Time for 10 revolutions
Median time for 10 revolutions
Radius minus (-9mm)
which is center of mass
to the center of the tube.
Measured radius of the circular
motion. Breakpoint to the center
of the tube.
Calculated results for the casting weight (see the THEORY section for the formulas):
Calculated Results
Period (T) of revolution for the weight
Velocity (v) of the weight
Centripetal acceleration (ac) of the weight
Net centripetal force (Fc) on the weight
(a)
What supplies this force, or what kind of force is responsible for the centripetal
acceleration? (Note: you may have to do the diagram first to answer this question)
Provide a free-body diagram of the situation (Indicate both the diagram for the hanging
mass and the revolving casting weight):
Calculated results for the hanging mass (see the free-body diagram for clues):
Calculate the tension in the string: ______________________________ (b)
Compare our theoretical result for the centripetal force (a), the free-body diagram, with
the measured dynamical value for the force (b). Since these are technically both
measured we shall calculate the percent difference as follows:
which is to say that it is the absolute value of the difference of the two values divided by
the average of the values times 100. This is solely because both values in the comparison
are measured.
Percent difference in net centripetal forces: _________________________
Describe at least three major sources of error.

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