Did you complete the reading assignment?
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KEY CONCEPTS:
1) The Venturi Effect is
a specialized from of Bernoulli's Principle.
2) Lift is a force that is a result of
pressure differences from fluid flow and Newton's laws.
The Venturi Effect states that the pressure and velocity of a fluid are
inversely related to each other. Since this concept was covered with
Bernoulli's Principle in the last reading quiz we will not look any more
into the Venturi Effect during this reading quiz, but feel free to go back
to reading quiz 21 or the key for reading quiz 21 if you are struggling to
understand this concept.
Lift is a force related to Bernoulli's Principle and the Venturi Effect.
Lift is caused by a difference in pressure in a fluid on different sides of
an object. This difference in pressure applies a force on an object in a
direction perpendicular to the direction of fluid flow. This principle has
been adapted to technologies like wings on a plane; where the object moving
through a relatively stationary fluid acts the same as a stationary object
in a fluid that is flowing.
Go to this nifty NASA applet:
http://www.grc.nasa.gov/WWW/K-12/airplane/foil2.html. There are a ton of
options that you can change on this simulation, but we will only look at a
few of them. Make sure to leave the flow setting on ideal flow. You can
change the units from 'English Units' to 'Metric' if you'd like, but I
prefer keeping it on 'English' units because I have a better understanding
of pounds that Newtons. Directly above the animation part of the applet you
have the option to change the view and display. Change the view to 'Side
3-D' and the display to 'Moving'. Notice on the right hand side there is a
plot of the pressure of the airfoil for the pressure under the wing (yellow)
and above the wing (fuchsia). Above this plot shows the magnitude of the
lift force. The three settings you will change on the airfoil will be the
angle of inclination, the camber, and the thickness. The angle of
inclination is the angle that the front end of the wing is with respect to
the horizontal, the camber deals with the shape of the concavity of the
wing, and the thickness is the percentage of how thick the wing is compared
to how wide the wing is. Don't worry too much about the units for camber or
thickness; focus on the effects they have on airflow and lift.
Play with the 3 airfoil settings mentioned above while watching the pressure
graph, lift force, and airflow animation.
Under what conditions will the lift force be in a downward direction rather
than an upward direction?
When the lift force is positive, which part of the wing has a greater
pressure?
Top of wing
Bottom of wing
Pressure is the same at all parts
When the lift force is positive, which part of the wing has a faster
airflow?
Top of wing
Bottom of wing
Airflow is the same at all parts
As the angle of inclination is increases (for positive lift), what happens
to the lift force?
Lift force increases
Lift force decreases
Lift force does not change
As the camber increases (for positive lift), what happens to the lift force?
Lift force increases
Lift force decreases
Lift force does not change
As the thickness increases (for positive lift), what happens to the lift
force?
Lift force increases
Lift force decreases
Lift force does not change
Which of the three factors influences lift force the least?
Angle of inclination
Camber
Thickness
It would be really cool if humans could fly without the aid of technology.
Lets see if Usain Bolt, the current World Record holder in the 100 m and 200
m dashes can fly. Change the airfoil shape (found just under the animation
part of the applet) to 'Ellipse' to make is shaped more like an arm. Also
set the camber to about -10% and the thickness to about 25% so that we are
getting the closest representation to an actual arm that we can. Also change
the angle of inclination to 20% which would mean that as he runs he would
need to hold his arms straight out to the side with his palms raised up to a
20° angle above the horizontal. Change the model under 'Student Mode' to
'Stall Model' to give a more accurate model of how air will actually act
around the arms. Now change the input type on the right side of the screen
(in blue) to 'Flight Test'. Bolt is estimated to have max out at about 27.2
mph at his top speed and weighs 190 pounds. If he can match this top speed
while holding his arms straight out at a 20° angle of inclination could he fly on an average Earth
day at sea level?
Yes
No
Provo's altitude is about 4500 feet above sea level. If I weigh 175 pounds, how
fast would I need to run on an average Earth day to fly?
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