An Experiment on Air Speed and Lift Force
An activity from the Burroughs Wellcome Student Research Program
Flight: From Butterflies to Boeing

Air Speed and Lift Force

When any object flies through the air, there are three basic forces that depend on the shape and air velocity of the object. These are weight, drag force (also called air resistance) and lift force.

What is the relationship between air velocity and Lift Force?
Based on what you know so far, predict the shape of the graph when air velocity is plotted with lift force for a sphere.

In this lab, you will measure the lift force on a sphere (beach ball) for various air velocities and determine the relationship between the two. You will use your manometer to measure velocity and a CBL Force Sensor to measure the lift force on a beach ball.

In both parts, be aware of how far the leaf blower is from the manometer and beach ball. You want this distance to be as constant as possible throughout the lab.

Part 1: Measuring Air Velocity

The leaf blowers are very strong. Make sure there are no loose objects in its path and that one lab member holds the manometer still.

1. Turn the leaf blower on its lowest setting and position the blower so it blows ACROSS the top of manometer. Adjust the angle of the blower until the largest displacement of water occurs. Record the change in height and speed.
   
   
2. Plug the blower into a Variac. The Variac allows you to adjust the voltage entering the blower and thus the speed of the air. Choose 5 different settings and record both the Variac setting and the air speed.

Part 2: Measuring Lift Force

The leaf blowers are very strong. Make sure there are no loose objects in its path and that one lab member holds the manometer still.

Using the Force Sensors with CBL

• Turn on the calculator and the CBL. They should already be connected to each other and the force sensor. Press the PRGM key on the calculator. Choose the program PHYSCI.
  
  
• You must first calibrate your force sensor so choose 1: SET UP PROBES Follow the instructions on the calculator. You have 1 student force probe in channel 1. Choose to PERFORM NEW calibration. You will calibrate your force sensor in Newtons. The two forces you will use are 0 N (no force) and the weight of weight of a 0.5 kg mass: W = mass x 9.8 m/s2 when the mass is in kilograms.
  
  
• You are now ready to collect data. Choose 2: COLLECT DATA
  
  If for some reason you quit the program or turn the calculator off, you will need to calibrate again!

Using the Force Sensors with CBL2/LabPro

• Turn on the calculator and the LabPro. They should already be connected to each other and the force sensor (in Channel 1). Press the APPS key on the calculator. Choose the DataMate program.
  
  
• You must first calibrate your force sensor so choose 1: SETUP. Make sure the curser is next to CH 1 and the force sensor is recognized by the LabPro. Press 2 to calibrate the sensor and 2 for CALIBRATE NOW. You will calibrate your force sensor in Newtons by following the instructions on the calculator. The two forces you will use are 0 N (no force) and the weight of a 0.5 kg mass: W = mass x 9.8 m/s2 when the mass is in kilograms.
  
  
• When you finsih, return to the main menu and press 2 to collect data.

 

1. Tie one end of the string to you beach ball and the other end to the hook on the force sensor.
   
   
2. Have one lab member hold the force sensor against the table so that the balloon pulls up on the rod.
   
   
3. Aim the leaf blower so it blows the ball straight up. Observe the force values given on the calculator. Try to get the force as constant as possible. Record the average force.
   
   
4. The force sensor measures the net or total force on the ball. This includes the lift force AND the weight of the ball. Determine the lift force provided by the blower and enter it in your data table.
   
   
   
   
5. Graph your data on Microsoft Excel.
   
   
   • In the first block (A1) type a title for your air velocity data and list them below in column A. Do the same for your lift force data in column B.
     
     
   • Highlight all of your data and nothing else. Click on the Chart Wizard button (a bar graph with a wand) and click again anywhere on the spreadsheet.
     
     
   • Click NEXT, choose a SCATTER graph, click NEXT, choose format #1, click FINISH
   • You can adjust the position and size of your graph by click and dragging on the border.
     
     
   • To title and label axes click INSERT at the top of the screen and choose TITLES.
     

What is the relationship between air speed and lift force?
Was your hypothesis correct?

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