PHY 2425 - Engineering Physics I
Leader:
_________________________ Recorder:
__________________________
Skeptic:
_________________________ Encourager:
________________________
Materials
Laptop
LabPro (Top drawer)
Motion Detector (Top drawer)
Cart with Friction pad and
wireless force sensor
Bluetooth dongle
Pulley
Gram mass set (bottom drawer)
Mass Hanger (bottom drawer)
String
Introduction
In a previous lab activity you explored
the conditions for equilibrium to result for force vectors on a force
table. Namely you saw that the forces
had to add to zero. This is one aspect
of
Procedure and
Questions
1. Set-up the Track
If not already attached, attach the
wireless force sensor to the cart. Place
a stop near the end of the track opposite the rubber bumper. Position the side of the track with the stop
at the end of the table. Attach the
pulley to the track so that it hangs over the end of the table. Lift up the motion detector and set the switch
to the cart position. Place the motion
detector on the track near the bumper and adjust the sensor so that it faces
toward the pulley. Attach the motion
sensor to the DIG/SONIC 1 input on the LabPro.
Connect the LabPro to the computer and make sure that it has power. If not already done so, plug the Bluetooth
dongle into a USB port on the computer.
Double click on the LoggerPro icon 
to start LoggerPro.
2. Connect to the Wireless Force Sensor
Turn on the Wireless force probe. In LoggerPro click on the Experiment menu,
the click on Connect Interface, then click on Wireless and then click on Scan
for Wireless Devices. LoggerPro will
think for a minute or two and then give you a message box saying it couldn’t
find any devices. Click on Yes to scan
again and after a little bit, LoggerPro should give a list of the wireless
sensors it found. Make sure that the box
is checked that matches the name on your sensor, and no other. If you don’t get the list of available
sensors at this point contact your instructor.
Click on the Position label on the Position vs. Time graph and choose
Force from the list that appears.
In the following be sure to make any predictions
before carrying out the procedures.
Prediction questions are labeled with a P.
Adjust the screw on the cart
so that the friction pad makes contact with the track. Give the cart an initial push and check that
it noticeably slows. Place the cart on
the track so that the hook on the force sensor faces the pulley. Attach the string to force probe, drape it
over the pulley and suspend the mass hanger from it. Use the gram masses to adjust the mass on the
hanger so that the force exerted by the string just balances the friction. The cart should remain stationary but if you
give it a nudge it should move remain moving without noticeably speeding up or
slowing down.
Pull up the masses by the
string so that the string is slacked where it is attached to the force
probe. Click on the Zero… button, choose
the force sensor and then click OK. The
force sensor is now set up to read the force on the cart with force sensor by
the string. Carefully lower the masses
again so that the string is under tension.
Click on collect. Click on the Experiment menu and then click
on Store Latest Run (shortcut CTL+L) so that LoggerPro won’t delete your data
on the next run.
Q1) Is there a net force on the cart when it
remains at rest?
Q2) Is there a force exerted on the cart by the
string when it is stationary?
Q3) How does the force exerted by the string
compare to the force of friction exerted on the cart? (Hint:
Consider your answer to Q1))
You will give a slight tug on
the string to get the cart moving and then allow it to move on its own.
P4) Will the force increase, remain the same, or
decrease when you tug on the cart to get it moving? Explain your prediction.
P5) Once you release the cart and it is moving on
its own, will the force exerted by the string be greater, the same, or less
than when the cart is stationary?
Explain your prediction.
Click on collect, tug on the
string to get it moving and observe the force and velocity graphs.
Q6) Was the velocity constant once the cart was
moving on its own?
Q7) Did the force change during the tug? In what way?
Q8) Did this agree with your prediction?
(P4) Explain.
Q9) Once the cart was moving was the force that
you measured noticeably different than when the cart was stationary?
Q10) Did this agree with your prediction? (P5) Explain.
This time you will pull a
little harder on the string so that the cart moves faster.
P11) Once the cart is moving on its own how will
the velocity curve change? Explain.
P12) Once the cart is moving on its own, how will
the force curve change. Explain.
Click on collect, give the
string a sharper tug so that the cart moves faster and observe the velocity and
force graphs.
Q13) Once the cart was moving on its own, was the
velocity constant? Explain.
Q14) Did this agree with your prediction?
(P11) Explain.
Q15) Once the cart was moving on its own, did the
force change noticeably from when the cart was at rest?
Q16) When the cart was at rest the net force on the
cart was 0. Once the cart was moving on
its own, was there a net force acting on the cart? Use your observed data to explain your
answer.
Adjust the screw so that the
friction pad still contacts the track, but there is noticeably less
friction. Readjust the mass on the
hanger so that force exerted by the string just balances the friction again.
P17) If the cart is rest, will the force exerted
on the cart by the string be the same, more, or less than what you measured
previously.
Click on collect and measure
the force when the cart is at rest.
Q18) Was your prediction P17) correct?
Q19) What is the net force acting on the cart when
it remains at rest?
You will give the string a
tug to get the cart moving.
P20) Once you release the cart and it is moving on
its own, will the force exerted by the string be greater, the same, or less
than when the cart is stationary?
Explain your prediction.
Click on Collect, carry out
the procedure and observe the graphs of force vs. time and velocity vs. time.
Q21) Was you prediction P20) correct? Explain.
Q22) Was the velocity constant once the cart was
moving on its own?
Q23) What was the net force on the cart once the
cart was moving on its own?
Adjust the screw so that the
friction pad is completely off the track.
There will still be some friction between the track and wheels and
between the axle and the cart, but it should be noticeably less. Readjust the mass on the hanger so that force
exerted by the string just balances the friction again.
P24) If the cart is rest, will the force exerted
on the cart by the string be the same, more, or less than what you measured
previously.
Click on collect and measure
the force when the cart is at rest.
Q25) Was your prediction P24) correct?
Q26) What is the net force acting on the cart when
it remains at rest?
You will give the string a
tug to get the cart moving.
P27) Once you release the cart and it is moving on
its own, will the force exerted by the string be greater, the same, or less
than when the cart is stationary?
Explain your prediction.
Click on Collect, carry out
the procedure and observe the graphs of force vs. time and velocity vs. time.
Q28) Was you prediction P26) correct? Explain.
Q29) Was the velocity constant once the cart was
moving on its own?
Q30) What was the net force on the cart once the cart
was moving on its own?
Summary Questions
S31) If you could completely eliminate the
friction on the cart, how much mass would you have to place on the hanger to
balance the friction?
S32) If you gave the frictionless cart a nudge to
get going, would it remain moving?
S33) Once it got going would the velocity be
constant?
S34) What would be the net force on the cart while
it was traveling at constant velocity?
Galileo first understood this
idea and
An
object at rest remains at rest and an object in uniform motion remains in
uniform motion unless a net force acts on it.