[MUSIC PLAYING] Good morning, everyone. Welcome
to your fluid mechanics experiment number three, measuring the drag force of a golf
ball and a smooth ball. In order to do this experiment, you need the wind tunnel. You
also need two balls– one, the smooth ball and, two, the real golf ball with a lot of
dimples. And also, in order to measure the force, you need the balance. The balance will
give you the directional reading of the force. I want to stress a very important thing for
this type of balance. That is, you need to lock the balance all the time when you handle
it. This is how you lock and unlock the balance. We have a screw over here. If you turn this
counterclockwise, this will release the balance. The balance will be able to measure the force.
Now, if you are turning clockwise all the way to the end, this will lock the balance. Now, remember the balance is a very sensitive
device. It will be able to measure the force accurate to 0.01 Newtons. So it is very sensitive.
And also, in the meantime, it’s very easy to be damaging. That’s why you need to lock
this device all the time when you handle it. So right now it is locked. So in order to measure the drag force of a
golf ball or a smooth ball, we need to mount the ball to the balance. Now, it’s going to
be your decision. Either you’re going to do the measurement for the smooth ball first
then golf ball second. Or you want to do this golf ball first, then you do the measurement
for smooth ball. It’s going to be your decision. I’m trying to measure the drag force of a
real golf ball first. So carefully slide this golf ball. You need to unlock this a little
bit. And, also, I want you to notice there’s a little pin over here. When you slide this
one in, you probably need to slide it in with a different angle, like this way. Then turning
around, you will be able to slide all the way down to the slot over here. Now you need
to lock in the golf ball. And the balance is also locked. Next step, we need to insert the golf ball
and the balance into the wind tunnel. Carefully insert the golf ball into the wind tunnel.
And also remember you need to align those two markers to make sure that the golf ball
is facing the direction of the airflow. Tighten the hatch. Then we need to also connect the balance to
the computer. The connection is here. There’s only one way you can connect this to the computer.
Lock the device. Now, the golf ball and also the balance are
ready to use. We can now power on the wind tunnel. And come over here to the computer.
Click on the software icon. And pick up Exercise E– that is the drag force graph and streamlined
bodies. Click on Load. You will see a pop-up window like this. Remember
to change the temperature from 18 degrees to 25 degrees, which is the room temperature
here. And also, as you can see, the watch dog enabled is illuminated, which means the
communication between the software and the computer and the wind tunnel are good. So
everything is ready to use. So before we start the measurement of the
drag force, we need to zero the software and also zero the physical balance quite a few
times. To zero the software, you just click on– there’s at Zero button over here. Click
on this multiple times. That’s it. So now the software has been zeroed. You also need to zero the balance. How do
we zero the balance? You just need to release the screw over here gradually, slowly. And
then tighten it. Do this multiple times. I usually do this to two to three times. Tighten
it, then gradually, slowly release this. So the physical balance now is zeroed. And the software is also zeroed. Now we can
start to measure the drag force. And we can say that is the software– as we said everything
is already ready to use. So we can give a fan potential equal to 20%. And you see the
wind tunnel right now start running. And we’ll also see that the software gives
us a reading about the drag force– you can read 0.04 Newton, which is good. And also
the velocity equals 7.6 meters per second. Those are the two data points you need to
record, the drag force and the velocity. So this is 20% percent. Remember, you have to wait for 60 seconds
to let its air flow become stable. Then collect your data. This is 20% now when this step
is finished. You can increase to 30% potential. Remember, wait for 60 seconds, air flow becomes
stable. And you need to record the drag force and also the air velocity from the software. This is 30%. Then increase this to 40%. [WIND FLOWING] Record the drag force and also the velocity.
In this case, the drag force is about 0.11 Newtons. And the velocity is about 13.5 meters
per second. So this is at 40%. Now you repeat the whole process for 50%,
60%, 70%, all the way to 100%. This is 100%. [LOUD HUMMING OF WIND] [WIND QUIETING] Remember, for 100% you also have to wait for
60 seconds to let the air flow become stable. Then you start recording your data of the
drag force and the velocity measurement from the software. OK? Now the second step you’re going to do is
try to repeat the measurement for the golf ball drag force one more time. So later we’re
going to take the average of those two sets of data for data analysis. So now we have
to wait for the fan– right now I can see the fan is still running– to be completely
stopped. When the fan is completely stopped, we need to zero the software, zero the balance–
as we said, multiple times– then start the measurement again. Just repeat the procedure
we just did. The fan is stopped. So now we can start zeroing
one more time. We zero the software. Click on this zero button quite a few times. And,
just as before, you need to tighten and then release those two or three times. Remember
to do this gradually and slowly. So I’m tightening. Lock the device. Now release gradually. So now the balance and the golf ball and also
the software are ready for– now, as you can see, you have to zero this one more time.
I see the number and not zero. So every time you notice it is not zero, you have to click
on the button quite a few times. So now the software and the balance– everything
is ready for the second measurement, one more time. So we just repeat the procedure as we,
you know, did before. So this is for the golf ball drag force measurement. Then, you need to change the golf ball to
a smooth spot to be able to compare the drag force between those two different balls–
smooth ball and the golf ball. Now we need to change the ball. Remember, now you are handling with the balance.
You need to lock the balance first. So I’m going to lock the balance. This is a very
important step. If you do not lock the balance, the balance could be easily damaged. So now
the balance is locked. Carefully remove the ball and the balance
from the wind tunnel. Release, turn around the golf ball. Replace it with the smooth
ball. Slide in like this way. Turn around. Then you will be able to slide this one all
the way to the slot. This is tight, and this is also locked. Carefully insert the smooth ball and the balance
into the wind tunnel. Then repeat the whole procedure as we just did for the golf ball.
Remember to zero the balance. Zero the software. Try different wind speeds, from 20%, 30%,
to 40%, with an increment of 10% all the way to 100%. Then repeat the whole process for
a second set of data. So that’s going to be your experiment for
fluid mechanics number three.