2. A student writes: "A basketball falls faster than a ping-pong ball because the basketball has less drag". Given that the drag force increases with an object's area, how would you correct their statement? Well, since the drag force is depending on the object's area So, it will be more In case of basketball than a ping - Pong ball SA , the ping - pong ball will fall Pastex 3. For what combination of an object's physical properties and speed through the air may we "neglect air resistance", as often assumed in science textbooks, and treat the object as falling under the influence of gravity alone? Well , we can neglect air resistance if the object across the sectional Surface area small or If the speed of object Is low 4a set of at least 4 nested aerodynamic decelerators (which resemble basket-style coffee filters), and a half coffee filter filter to ride as a "passenger" for some trials Kodak Zi8 video camera, set to 720P/60FPS Laptop computer (provided) use of an electronic scale to measure the masses of the objects we drop. 1-meter ruler for measuring drop distance. 3. Procedure From a stack of filters, count at least 5 filters but leave them nested together. Using the electronic scale, determine as accurately as possible the mass of a coffee filter, and describe how you did this in your lab notebook. To sample the dropped masses at a finer interval, take one of the filters and use a ruler to fold and rip it in half. This will be a "passenger" of approximate for some trials. To minimize changes in shape due to wear-and-tear, first drop a single filter for, then 1 filter + 1/2. Then place this filter inside a second "fresh" filter and drop both together, first without and then with the 1/2 filter, and so on (see Table 1). Perform a few "practice" trials to be confident with the method.. Lab partners should take turns at dropping filters, and recording times. For each trial: 1. Record the mass in grams of the object to be dropped (filters with or without paperclip), and calculate its weight Fg in Newtons. (Remember that on Earth: Weight in Newtons = Mass in kilograms times 9.8 m/s ). 2. Set the video camera to 720P/60FPS. Drop the filters next to the 1-meter stick held vertically, starting about 50cm above it. Make sure that you will be able to see the top and bottom of the meter stick in the video. 3. Transfer the video clip onto the Desktop of the PC, and open it with Quicktime Player. Change the time reading to "Frame" at the bottom left of the Quicktime display. 4. Record the start and end frame numbers for the coffee filters' motion past the ends of the meter stick, then use these to calculate (i) the fall time and (2) the terminal speed. 4. Analysis The aerodynamic drag law (Equation 1) predicts a simple relation (Equation 2) between terminal speed and weight for falling objects of the same shape. We can now test this relation. 1. Calculate the square of the terminal speed Of2. 2. Plot air drag force (=mg at terminal speed) vs. Or on the horizontal axis. 3. Use a full page of graph paper for this plot, and include the origin (0,0). 4. Draw the "best fit" straight line from (0,0) that passes closest to your data points. 5. Calculate the slope of this line as "rise divided by run", using the units on each axis.You may enter values directly into this table, or copy it neatly for a larger version. Sample calculations of terminal speeds and averages can be shown in your lab notebook. Drop height 1 filter 1.5 filters 2 filters 2.5 filters 3 filters 3.5 filters 4 filters H = 1.50 m. Mass m (gram) 1.32 1-98 2-64 3. 25 13.96 4. 62 5-2 Weight Fo= mg (milli-N) 12-9 19.40 25. 87 31-85 38.80 45-28 50 - 96 Start frame # 306 3 6 6 329 358 419 18 46 End frame # 410 438 398 419 10 3 70 96 Fall time to (s) 1.73 1 . 2 1.15 1- 02 0 . 9 0-87 0 . 83 time UT = It ( m/s) 10. 87 1.25 1.47 1.67 1-72 1.81 1. 30 (m:/ sz ) 10- 76 1. 56 1-69 2- 16 2- 79 2. 96 3- 28 From your graph of Fg (vertical axis) vs. Ur (horizontal axis), Best fit slope b = 1/2 CDPA kg/m. => drag coefficient of a coffee filter CD = Questions: 1. Referring to Equations 1 & 2, when a skydiver of mass 80kg falls at his terminal speed: a. What is his weight Fg = mg, in Newtons? b. What is the (i) net force acting on him, in Newtons, and (ii) his acceleration?. (i) Net Force. (ii) Acc c. Therefore, what must be the force of air resistance Fo acting on him, in Newtons? 3