Key Homework For Lab 4 Force And Motion

Unformatted text preview: ID Numm Lab TA Name AM— PRE-LAB PREPARATION SHEET FOR LAB 4: FORCE AND MOTION (Due at the beginning of Lab 4) % Directions: Read over Lab 4 and then answer the following questions about the procedures. 1. LVhat is the purpose of tl'fi‘rubber bands in Act'vity 1-1? \0 CcmOMQ w ' W {To * {m (.03 CR \WA‘VH \NM‘QS. 2. What is the difference between a linear and a proportional relationship? { A “flea. I'g‘kfln‘wfn v dl§(\\\3($ (K CLHNL't‘Dh UJhCl“ L‘ \r(\€r"’2 7“ i [50 I; ACLUUNXB kl kK'. mK‘b' A “"fi"»(‘t|.r‘l ‘9‘ .i_tv‘_h¢l- rPH‘IE h 0 K (3...” r \ km \th I. . mm "‘an u" :u‘ “u L ~u-uafl If $00- ' ' I a“ ' a )7 . I' r' t {r 3- ‘Y‘fh?_‘5\'\f““‘”f??.fi‘§°a“ fi°§f§ictfl°fing Mo Oxtmtvk km ‘ :1 m . “\ 4“ ‘ ' 4 ‘ 3m 1 Wet mtthjnm. 4. Sketch your Prediction 2-2 below. '\\ '\ "_‘ g E 2 0 8 4: Time 57 LAB 4: FORCE AND MOTION LU a}? FMM' ‘11 W. .mz'... .n.. J “Mia. $.44}; ; 1—" "' ’ Nam“ ID Number i Date _h:l—'1.ULT,\31 _ Lab Partner Lab 00-L Lab TA Name LAB 4: FORCE AND MOTION A vulgar A‘th‘rlwni am practice what he has lwn taught or semi done, but if he is in an error he knows no! hair lo find it out and mrrm‘ it, and if you put him out of his road, he is at a stand; :vln‘n‘as he that {5 able to reason nimny and judiciously about figurinfnrce and motion, is mfiw a! rest til he gets over every rub. —lsaac Newton OBJECTIVES 0 To develop a method for measuring forces reliably. 0 To learn how to use a force probe to measure force. 0 To explore how the motion of an object is related to the forces applied to it. 0 To find a mathematical relationship between the force applied to an object and its acceleration. OVERVIEW In the previous labs, you have used a motion detector to display position-time, velocity—time, and acceleration-time graphs of different motions of various ob- jects. You were not concerned about how you got the objects to move, i.e., what forces (pushes or pulls) acted on the objects. From your own experiences, you know that force and motion are related in some way. To start your bicycle mov- ing, you must apply a force to the pedal. To start up your car, you must step on the accelerator to get the engine to apply a force to the road through the tires. But exactly how is force related to the quantities you used in the previous lab to describe motion—position, velocity, and acceleration? In this lab you will pay attention to forces and how they affect motion. You will first develop an idea of a force as a push or a pull. You will learn how to measure forces. By applying forces to a cart and observing the nature of its resulting motion graphically with a motion detector, you will come to understand the effects of forces on motion. LAB 4: FORCE AND MOTION \9 \‘b 59 INVESTIGATION I: MEASURING FORCES ——___._—______________ In this investigation you will explore the concept of a constant force and the com- blnation of forces in one dimension. You can use these concepts to learn how to measure forces with a force probe. You will need the following materials: 0 computer-based laboratory system 0 force probe ° five identical rubber bands 0 meter stick 0 supplemental notes for Capstone software Activity 1-1: How Large Is a Pull? If you pull on a rubber band attached at one end, you know it will stretch. The more you pull, the more it stretches Try it. 1. Attach one end of the rubber band to something on the table that can't move. Also attach the meter stick to the table. Now stretch the rubber band so it is sev- eral centimeters longer than its relaxed length. Does it always seem to exert the same pull on you each time it is stretched to the same length? (Most people agree that this is obvious.) 2. Write down the length you have chosen in the space below. This will be your standard length for future measurements. Standard length of rubber Rubberband(s) band = _\§_cm ' 3. Attach one end of each of two identical rubber bands to some- thing that can’t move and stretch them together side-by- side to the standard length. Standard length Question 1-1: How does the combined force of two rubber bands compare to what you felt when only one rubber band was used? Th mt bin-cur \o w“ WWMW‘C‘ “it ‘5" men CHOW“ 4. Repeat this comparison of how strong the forces feel with three, four, and five rubber bands stretched together to the same standard length. Question 1—2: Suppose you stretched a rubber band to your standard length by pulling on it. Now you want to create a force six times as large. How could you create such a force? ~ 0 \pt. SN \{MOU lists-13 FH’H‘I 5 0% REALTIME PHYSICS: MECHANICS dQUEStltén 1-3: Suppose you applied a force with a stretched rubber band one {33" an several days later you wanted to feel the same force or apply it to some- t mg. How could you assure that the forces were the same? Explain. “54.. “M Some io‘rkK‘ \de Vctcfl’l‘ l’K V‘H\\ 0001“, his 8am Em, Question 1-4: _Do side-by-side rubber bands provide a convenient way of accu- rately reproducmg forces of many different sizes? Explain. \lt‘) ti. Mt Tam G‘i‘mm 45.1111 him film. 5mm thatch l\\u\ \‘M wow Miami fumes 0mmin or. how mung WWW \ \)(\u(\l use use, You have seen that pulling more rubber bands to the same length requires a larger pull. To be more precise about the pulls and pushes you are applying, you need a devrce to measure forces accurately. The electronic force probe is designed to do this. Activity 1-2: MeaSuring Forces with a Force Probe In this activity you will explore the capability of an electronic force probe as a force measuring device. 1. Plug the force probe into the computer interface. Display force vs. time axes by opening the experiment file called Lab4.cap from the class notes folder; and navigate to the tab named Measuring Force. When you use the force probe, go ahead and leave it attached to the dynam- ics cart (if it is already attached to it). Comment: Since forces are detected by the computer system as changes in an electronic signal, it is important to have the computer “read” the signal when the force probe has no force pushing or pulling on it. This process is called "zeroing." Also, the electronic signal from the force probe can change slightly from time to time as the temperature changes. This is especially true with a Hall effect force probe. Therefore, if it is possible to zero your force probe, it is a good idea to do so with nothing attached to the probe before making each measurement. 2. Zero the force probe with nothing pulling on it by pushing the "Tare" button on the side; always remember to do this right before you use the force probe. 3. Attach one end of a rubber band to something that can’t move, as before, and the other end to the force probe hook. Pull horizontally on the rubber band with the force probe until the band is stretched to the same standard length used in Activity 1-1, and begin graphing while holding the rubber band steady for the whole graph. ’1 Record a typical force probe reading: 3 'b Check the supplemental notes for this activity. LAB 4: FORCE AND MOTION 61 4- Although you could continue to take data with multiple rubber bands in the same way you did with just one, the easiest way to take these data is to nav- igate to the tab named Rubber Bands. Read the supplemental notes for this activity for instructions on using the keep function and previewing data. Keep (by pressing the "KEEP" button) the force values with 0, 1, 2, 3, 4, and 5 rubber bands pulled by the force probe to your standard length. Stop graphing when you are done. Comment: We are interested in the nature of the mathematical relationship between the reading of the force probe and force (in rubber band units). This can be determined from the graph by drawing a smooth curve that fits the plotted data points. Some definitions of possible mathematical relation- ships are shown below. In these examples, y might be the force probe reading and x the number of rubber bands. y Intercept x (0.0) y is a function of x, which in- y is a linear function of x, which y is proportional to x. This is a spe- creases as x increases. increases as x increases according cial case of a linear relationship to the mathematical relationship where y = mx, and b, the y inter- y = mx + b, where b is a constant cept, is zero. called the y intercept. These graphs show the differences between these three types of mathematical relationship. y can increase as x increases, and the relationship doesn’t have to be linear or proportional. Proportionality refers only to the special linear relationship where the y intercept is zero, as shown in the example graph on the right. 5. Using the supplemental notes as a guide, try matching a curve to your data. You may want to try several different types of curves to see which one “fits” best. KY bwf ’6 Oh C1\ 62 REALTIME PHYSICS: MECHANICS W-i .._ -‘ ‘ Quesnon 1'5: Based 0“ YOUI graph, What force probe reading corresponds to the pull of one rubber band wh t t h d t 7 . yo dew - e t '8? en 5 re c e 0 your standard length. How drd \ 3.55:) \k was "one. Porto. retardant) New we done: cm WWW \mct hmmwmfl Locum} at ‘llM mes QDY one “NOW \OOV‘Cl and mmth 9“ CorfiSQOYWOWc) (obrmmfrt . W‘fi PWC‘ 'llfl U \tuWe. Comment: You can use your measurements to define a quantitative force scale. You might call it the "rubber band scale," or give it yours or your part- ner's name. Whenever the force probe has the reading corresponding to the pull of one rubber band stretched the standard length, the force is equivalent to one "rubber band," or one "Mary" or one “Sam.” Any larger force can be measured as some number of these units. Your graph relates two different ways of measuring force, one with stan- dard stretches of different numbers of rubber bands (rubber band units) and the other with a force probe. Such a graph is called a calibration curve and is used to compare measurements of quantities made with two different mea- suring instruments. You could use it to convert forces measured in force probe units to rubber band units, and vice versa. Physicists have defined a standard unit of force called the newton, abbre- viated N. For the rest of your work on forces and the motions they cause, it will be more convenient to have the force probe read directly in newtons. Then the forces you measure can be compared to forces anyone else measures. Most spring scales have already been calibrated in newtons. All you need to do is to calibrate the force probe to read forces in newtons by using the spring scale to input standard force measurements. LAB 4: roncr AND MOTION 63 L . ______ Wm— ,__ _ l INVESTIGATION 2: MOTION AND FORCE _________________________—._- Now you can use the force probe to apply known forces to an object. You can also use the motion detector, as in the previous two labs, to examine the motion of the Object. In this way you will be able to explore the relationship between motion and force. You will need the following materials: ° computer‘based laboratory system ' force probe ° rotary motion sensor to detect the motion (make sure the string is going around the LARGEST of the rotary motion sensor pulleys) 0 cart with very little friction ' masses to increase cart's mass to about 1 kg 0 smooth track or other level surface 2-3 m long ' low-friction pulley, lightweight string, table clamp, variety of hanging masses 0 supplemental notes for Capstone software Activity 2—1: Pushing and Pulling a Cart In this activity you will move a low friction cart by pushing and pulling it with your hand. You will measure the force, velocity, and acceleration. Then you will be able to look for mathematical relationships between the applied force and the velocity and acceleration, to see whether either is (are) related to the force. 1. Set up the cart with force probe attached on a smooth level surface as shown below. Just use the cart and force sensor with no additional mass on the cart. Instead of the motion detector shown in the figure you will be using the ro- tary motion sensor. Attach the string to the cart, route it over the largest of the rotary motion sensor pulleys, and hang a 50 gram mass from it (the 50 gram weight hanger with no additional masses is perfect for this). Motion Detector Coho. / %WW/WW//WZ Prediction 2-1: Suppose you grasp the force probe hook and move the cart for- ward and backward in front of the motion detector. Do you think that either the velocity or the acceleration graph will look like the force graph? Is either of these motion quantities related to force? (That is to say, if you apply a changing force to the cart, will the velocity or acceleration change in the same way as the force?) Explain. “C I“, w“ \uot. \sv/L M W W“ l" “3 - intake. ‘3 W (wm‘i' (Mug and Lie -’_r_ REALTIME PHYSICS: MECHANICS mum-“'-c- “.3'3“ gl‘. in I I I I i] "I “1". —' 2' T0 test your PredictiOnS, naVigate to the tab named Motion and Force. This wall set up velocity, force, and acceleration axes with a convenient time scale of 5 s, as shown below. +1 Velocity (m/s) 0 Acceleration (nu/32) Time (s) 3. Zero the force probe. Grasp the force probe hook and begin graphing. Pull the cart quickly away from the pulley and stop it quickly. Then push it quickly back toward the pulley and again stop it quickly. Try to get sudden starts and stops, and to pull and push the force probe hook along a straight line paral- lel to the track. 4. Carefully sketch your graphs on the axes above. You may need to re—scale the axes to show all of your data. Question 2-1: Does either graph—velocity or acceleration—resemble the force graph? Which one? Explain how you reached this conclusion. M r. ,. v “ Afffillml’lm VEAQHWWS 1 (21.3“ ,. L f. \mm are; Poms wank co, \JXUL \lQ\5 (x o - 4y )U\.n\l\ P);le y” .JJ". ' . I {-k I ) LAB 4: FORCE AND MOTION 65 Question 2-2: Based on your observations, does it appear that there is a mathc; ematical relationship between either applied force and velocrty. appllEd force an acceleration, both, or neither? Explain. "lime \3 a immrmhml {WHO'W‘O “WW OQWTH‘NQ' Ohd aucumflon. mmm Pomp was hqt a((gl1m+mu r ‘ r max)“ (35(qu 4m; we“ "fffik. Ham 4 “0.8- \Mi 6N} .\~U‘~ W bf To; «We (Nam ‘mwm mr.‘ INN-"i Actuvuty 2-2: Speeding Up Again flwmmr .n gt Maui .mvn 5cm:- tf m it“ “HM-o DHQv-x deuawx You have seen in the previous activity that force and acce eratlon seem to be re- lated. But just what is the relationship between force and acceleration? Prediction 2-2: Suppose that you have a cart with very little friction and you pull this cart with a constant force as shown below on the force—time graph. Sketch 0n the axes below your predictions of the velocity-time and acceleration—time graphs of the cart's motion. PREDICTION Acceleration Time REALTIME PHYSICS: MECHANICS In“. 2.1.1 rm; “A an a 423:.“ M e ~W‘W ' ’v’ '* Describe in words the predicted shape of the velocity vs. time and acceleration vs. time graphs that you sketched. if) i f tuft - “Ming \D\\\ «new oi 0 mm it {mstant ancllmtttvc. Atttttwthm at 1. Test your predictions. Set up the ramp, pulley, cart, string, and force probe as shown below. The cart should be the same mass as before (about 1 kg). At least 1.5 m to floor Be sure that the cart's friction is minimum. (If the cart has a friction pad, it should be raised so it doesn’t contact the ramp.) 2. Prepare to graph velocity, acceleration, and force. Navigate to the tab named Speeding Up Again to display the velocity, acceleration, and force axes that follow. 3. It is important to choose the amount of the falling mass so the cart doesn’t move too fast to observe the motion. Experiment with different hanging masses until you can get the cart to move across the ramp in about 2—3 s af- ter the mass is released. (Note: For this and the next parts, use the 5 gram weight hanger. Don’t use a combined total mass greater than 55 grams. The smallest reasonable mass to use is about 15 grams.) 553 4. Zero the force probe with the string hanging loosely so that no force is ap- plied to the probe. Zero it again before each graph. 5. Begin graphing. Be sure that the cable from the force probe doesn’t drag or pull the cart. 6. Consult the supplemental notes for instructions on how to save your data for later analysis. If necessary, adjust the axes to display the graphs more clearly. Sketch the actual velocity, acceleration, and force graphs on the axes that fol- low. Draw smooth graphs; don’t worry about small bumps. Record the hanging mass that you decided to use: LAB 4: FORCE AND MOTION 67 _—‘—h '1' —I‘—_ .‘-b‘(‘ FINAL RESULTS +2- Velooity (m/s) 0 l M Acceleration (nu/52) l + M O M a...“ u._.___ A _ 4 o .6 " 1.2 1.8 2.4 3.0 Questions 2-3: er the cart is moving, is the force that is applied to the cart by the string c ' stant, increasing, or decreasing? Explain based on your graph. The (We: is (005’me 12+ \3 o stone homeow- ' Lt m oath» Question 2 : How does the acceleration graph vary in time? Does this agree with ‘ your prediction? Does a constant applied force produce a constant acceleration? Attctcrahon i5 (onslant ate, lama (hump. aNm enzyme; “pup swat 'Fldlthm. ‘1“) 0. (0055mm Gr’PltK‘i prch product; marlin“ WIUU‘; Question 2-5: How does the velocity graph vary in time? Does this agree with your prediction? What kind of change in velocity corresponds to a constant ap- - 7 plied force. “(b— 0{ WWW...) "Kama “moqrm mfi’n WV {harlfo W. m (n l" l \ 0* 0 COM“ 0!“ Ink “WA ant, ifih‘ ail-{bra} ' L Activity 2-3: Acceleration From Different Forces In the previous activity you examined the motion of a cart With a constant force applied to it. But what is the relationship between acceleration and force? If you apply a larger force to the same cart (while the mass of the cart is not changed) how will the acceleration change? In this activity you will try to answer these questions by applying different forces to the cart, and measuring the corre- sponding accelerations. REALTIME PHYSICS: MECHANICS It you accelerate the same have three data p can then find the the mass of the cart with two other different forces, you will then mnts——enough data to plot a graph of acceleration \'5. force. You mathematical relationship between acceleration and force (with cart kept constant). Prediction 2-3: Suppose you pulled the cart with a force about twice before. Wh at would happen to the acceleration of the cart? Explain. 4}“ an (\(flmt‘i “mid \K “5’ V9 “‘5 (0" “K 05 it! *0“ he unfit W0": h\{\ §\hu. Y7mh| |£ Ann‘th ‘hfi 1((f'hotfllh' dth to“ Marni“ GTQ Ofiqdrk (floAQA. 1. Test your prc iction. Kee on the screen. as large as in I‘ .2 ‘9” 1 J p the graphs from Activity 2-2 persistently displayed 2. Accelerate the cart with a larger force than before. To produce a larger force, hang a mass about two times as large as in the previous activity. Record the hanging mass: 625 3. probe with nothing enriched to the hook right before graphing. 4. Sketch your graphs as well as the graphs from Activity 2-2 on the axes below. You can relabel the numerical value 5 on the vertical aXes if necessary to get a more reasonable range. FINAL RESULTS +2 Velocity (tn/s) Acceleration (I'D/82) Graph force, velocity, and acceleration as before. Don't jor‘ec'! to zero Hu'firm’ ! 69 LAB 4: FORCE AND MOTION 70 Table 2-3 _ Average force (N) Average acceleration (mlsz) Activity 2.3 , S a . r 5- Using the supplemental notes as a guide, find the average acceleration of the cart and the average force applied to the cart. Question 2-6: How did the force applied to the cart compare to that with the smaller force in Activity 2-2? ,“ I ,x- wa' ‘-\‘0\ox‘.nmltlt\ tND Him w r0”: lent riot “mil yaccubic ‘.ui' (lid Mimexaztlvt two “It”! “1* Wildfi- Question 2-7: How id the acceleration of the cart compare to that caused by the smaller force in Activity 2-2? Did [this agree with your rediction? Explaint 1+ was (invarinutf'xi two hilt“ 0U) “lira.- hJ, rot Mavis... 4. ’i' ' ' .2 (drum-'1 dway between the other two forces 6. Accelerate the cart with a force roughly mi dway between those used before. you applied. Use a hanging mass about mi Record the mass: 1 5 ‘3 '7. Graph velodty, acceleration, 8. Find the mean acceleration and force, bottom row of Table 2-3. and force. Sketch the graphs on the previous axes. as before, and record the values in the Carry out the following Extension to get more data for the acceleration vs. force graph you will make in the next activity. Extension 2—4: More Acceleration vs. Force Data Gather data for average acceleration and plied to the same cart. Put your data in Reasonable total hanging masses to u redo ones that you have already done in Activity 2-2 or 2-3). the remaining three rows in Table 2-3. Activity 2-5: Relationship Between Acceleration and Force In this activity you will find the mathematical relationship between acceleration and force. 1. Navigate to the tab named Acceleration vs. Force, and enter your data from Table 2-3 in the table that appears in the tab. You may wish to adjust the graph axes, after all of the data are entered. REALTIME PHYSICS: MECHANICS ' “h '. Jflfl and, 2' Try fitting a curve '0 Your graph and. once you are satisfied, print the data. Refer to the supplemental notes for printing instructions Question 2-8: Does there appear to be a simple mathematical relationship be— tween the acceleration of a cart (with fixed mass and negligible friction) and the force applied to the cart (measured by the force probe mounted on the cart)? write down the equation you found and describe the mathematical relationship in words. \les.+he ttmhmghm i3 yrboomtcml. ‘l-‘X Question 2-9: If you increased the force applied to the cart by a factor of 10, how would you expect the acmleratiou to change? How would you expect the accel~ eration—time graph of the cart's motion to change? Explain based on your graphs We “MU Mitt. anfluflow {-0 Change matador bl +60 . Arrangith HM Wm WWW 5houo Cm Magma \t'\ H$ \f (oo‘td‘naifJ taxi l0. Question 2-10: if you increased the force applied to the cart by a factor of 10, how would you expect the velocitywtime graph of the cart's motion to change? Explain based on your graphs. m 9on ol Wquoul’Lj lame (Xiaph WWW mails Io cm \16 WUOA new, 5W0 Fm" our o‘mphC, flu nlflqnl'ludjd ngt \l‘ Greased what/1 Q (Suqfir Ft)ch ML“ (ipplitd, Comment: The mathematical relationship that you have been examining be- tween the acceleration of the cart and the applied force is known as Newton ’5 second law. In words, when there is only one force acting on an object, the force is equal to the mass of the object times its acceleration. LAB 4: FORCE AND MOTION 71 e with the lab, PLEASE tidy up your station. IMPORTANT: After you are don ed back in their holder. In particular, please put any weights you us Al 10 minutes before the end 0f your lab period, you should are working on and skip to the "Post-lab questions for Lab 4" next page. Do the questions there. When you are done, staple all pages of your report together, including the post-lab, (staplers can be found on the TA's table). and give it to your TA. ml“ "' ‘ POST-LAB QUESTIONS FOR LAB 4: FORCE AND MOTION Questions 1—3 refer to an object that can move in either direction along a hori- zontal mile (the + position axis). Assume that friction is so small that it can be ne— glected. bketch the shape of the graph of the force applied to the object that would produce the motion described. 1. The object moves away from the origin with a constant velocity. 2. The object moves toward the origin with a constant velocity. 3. The object moves away from the origin with a steadily increasing velocity (a constant acceleration). Questions 4 and 5 refer to an ob- ject that can move along a horizontal line (the + position axis). Assume that friction is so small that it can be ignored. The object’s velocity—time graph is shown on the right. LAB 4: FORCE AND MOTION Time 73 4. Sketch the shapes of the acceleration-time and forcehtime graphs on the axes below. Acceleration Force Time (s) 5. Suppose that the force applied to the object were twice as large. Sketch with dashed lines on the same axes above the force, acceleration, and velocity. 6. An object can move along a horizontal line (the + position axis). Assume that friction is so small that it can be ignored. The object's velocity—time graph is shown below. Acceleration 74 REAIJ'IME PHYSICS: MECHANICS A Set2 ‘ 0 Set Average . Average ‘kcekrafion 1 Force Lmur I (Wsz) nu ‘- b 7-0 3 -o 3 rr - no 2 o o ' ' 4; b n n no : oo . ‘0 S i :0 5 v- 109:: -0‘ ' ~04 7 J -o 2 ’ o 2 fi‘ '0 1 -0 1 it ‘ E [:3 = ‘ .9 ' s ‘5 7*. a I 2 i l V; 3 i = < ‘- I: J 1' . ; g ‘ ‘ < i. A | I ‘ ‘ ‘w ‘ ‘ \ 1 I -o 5 4): »o 3 -o 2 .o 1 o o i u ‘ 4 Average Force (NI 1 _ f 7_, _J WWV______.__ _____.777 7 7 77 _. 7 7 7 . . . .._.. ...
View Full Document

Да вроде бы, - смущенно проговорил Беккер. - Это не так важно, - горделиво заявил Клушар.  - Мою колонку перепечатывают в Соединенных Штатах, у меня отличный английский. - Мне говорили, - улыбнулся Беккер. Он присел на край койки.

0 Replies to “Key Homework For Lab 4 Force And Motion”

Lascia un Commento

L'indirizzo email non verrà pubblicato. I campi obbligatori sono contrassegnati *