LAB REPORT Tub Experiment Victor Blum, 8C, April, 30 2019 Research Question Does the pullback length of a rubber band (I.V, cm: 15, 25, 35, 45, 55) affect the distance (DV, cm) of a propelled tub? Context / Background By measuring the distance the tub travels when propelled by the release of the rubber band, this experiment enables a better understanding of the relation between the stretch of the band and the distance the tub travels. Newton’s Second Law states that an object will stay in motion until an outside force acts on it. Thus, as the tub travels across the floor, it is expected that it should decelerate. The forces which operate on the tub are the force which is transferred from the rubber band, the drag from the air and friction from the ground; the resultant force determines the distance the tub travels. It is clear from Hooke’s law, when a force is applied on an object, an equal force pointing in the opposite direction is stored throughout the rubberband and will release itself when the outside force is removed by going back to its original shape. This force stored inside the rubber band is called Potential energy and when it is released, the potential energy becomes Kinetic energy as the stretched elastic band compresses. It seems clear, therefore, that the pullback of a rubber band will have an impact on the amount of force transferred to the tub and as a result, how far it travels. Hypothesis If the stretch of the pullback is increased (cm: 15, 25, 35, 45, 55), then the tub will travel a longer distance (cm), because the acceleration of the band to get back to its original force also increases therefore enlarging the amount of potential energy transferred to the tub. Variables Table 1: Variables Variables Independent Variable Distance the rubberband is pulled backed Range How it can be controlled (Centimeters) - 15 25 - 35 - 45 - 55 (10 centimeter difference between each pullback length) To investigate what happens when the stretching distance is changed uniformly: 15, 25, 35, 45, 55 - every 10 cm of change LAB REPORT Tub Experiment Victor Blum, 8C, April, 30 2019 Dependent Variable Controlled Variables Distance the tub has travelled (measured in Centimeters) after the launch. N/A The distance the tub travelled or covered after its launch. depends on the distance the rubberband is pulled back. N/A The surface is the floor of the classroom which is the same throughout the replications. This surface is obstacle free. - Surface - Size of Tub To ensure that the data collected is reliable, the same tub will be used for all 15 trials. - Mass of Tub (g) No additional weights were added to the tub in any trial, the tub’s mass remained the same throughout at approximately 20g - Chair Used Throughout the different trials, the chair used is the same so the result is not affected by the chair - Height of Rubber band (cm) In all of the trials, the rubber band was attached to the chair at the same height off the floor. This meant that when the rubber band was pulled back on a plane, the angle of its release and contact with the tub would not alter between replications. Were the rubber band to make contact with the tub at a different point in each replication then the action of friction and drag would be slightly different in each replication lessening the data’s reliability. - Number of Rubber bands used The same type, the same brand, the same size and the same quality of the rubberband to ensure the result is reliable. - Temperat ure and Since the experiment was done at the same time, under the same environment and under the same LAB REPORT Tub Experiment Victor Blum, 8C, April, 30 2019 Surroundi ng room temperature. Moreover, it was ensured that no windows were open to cause any external disturbance while the experiment was conducted. Materials Table 2: List of materials required Material Number Use Photo Chair with four stable legs. 1 To hold the rubber bands and act like a slingshot. Fig.1 Tub 1 Object propelled by the rubber band Fig. 2 Meter Stick 2 To measure the pullback distance of the rubberband and to get more accurate results of the launch distance. Fig. 3 Tape Measurer 1 Aligned against the wall to measure the distance the tub travelled. Fig. 4 LAB REPORT Tub Experiment Victor Blum, 8C, April, 30 2019 Rubber bands 2 Used as a slingshot to propel the tub Fig. 5 Method 1. Get a chair with four sturdy legs and place it on the floor. 2. Get 2 rubber bands and tie them together. 3. Place the rubber bands on the 2 front legs of the chair. 4. Extend the tape measurer along the wall to calculate the distance the tub will travel. 5. Place a meter stick behind the two front legs of the chair to measure the rubber band pull back. Ensuring that is starts at zero to avoid any errors when stretching the rubber band. 6. Use the second meter stick during the experiment to calculate the exact distance the tub will travel by placing it behind the tube and aligning it with the tape measurer. 7. Now, pull the rubber band back to the length of exactly 15 cm (measuring with the ruler) and place tub release. 8. Record the distance the tub has travelled by using the measuring stick to get more accurate results. 9. Repeat the experiment three times with the same stretching distance of 15cm each and record the distance the tub has travelled every time using the measuring stick ensuring a reliable and unbiased results. 10. Now with the pull back distance of 25cm, repeat step 7, 8, and 9 and continue to record the distance by changing the pull back distance of the rubber band to 35, 45, 55cm respectively and record the distances well for every three trials of each distance changed. 11. Calculate the average distance travelled for each pullback distance ( 115, 25, 35, 45, 55cm respectively) and create a table with the findings. Table 3: Data Processing Pullback Length (cm) Distance Travelled (cm) Average LAB REPORT Tub Experiment Victor Blum, 8C, April, 30 2019 Trial 1 Trial 2 Trial 3 distance travelled (cm) 15 193 199 201 198 25 343 310 297 317 35 516 462 470 483 45 727 717 640 695 55 1040 798 780 873 Figure 6: Rubberband pullback vs. distance travelled Analysis of the graph As evident from table three, with every change in the pullback length of the rubberband, the average distance traveled by the tub increase. When the rubber band is pulled back 15 centimeters, the average distance traveled is 198 centimeters. When same rubber band is stretched to 25 centimeters (A distance of 10 centimeter difference), then the average distance traveled is 317, which is a 109 centimeter difference for a 10 centimeter change. At a 35 centimeter pullback, the average distance traveled is 483 centimeters. Which is nearly 166 centimeter from the previous one. If I continue to look at the pattern, in the next step, when the distance the rubberband is pulled back is 45 cm, the average distance is 695 centimeter which LAB REPORT Tub Experiment Victor Blum, 8C, April, 30 2019 is showing a pattern of 212 centimeter increase from the previous one. Finally the stretching of 55 centimeters, the average distance travelled is 873 showing an increase of a 178 Trend In this experiment, there were multiple pattern. One being the further you pull back the rubberband, the further the tub would travel. But, there was one that took me some time before noticing it. After the experiment, using Hooke’s law of elasticity, I noticed that everytime we did the experiment, the rubber band elasticity would decrease Table 4: The trend Pull back length of rubber band in cm Average distance travelled by tub in cm Difference is average distance travelled by tub in-between intervals in cm Percentage increase or decrease 15 198 198-0 = 198 100% 25 317 317-198 = 119 317 − 198 ( × 100) 198 = 60.1% 35 483 483-317 = 166 ( 317 × 100) = 52.4%% 45 695 695-483 = 212 695 − 483 ( × 100) 483 = 43.9% 55 873 873-695 = 178 873 − 695 ( × 100) 695 = 25.6% 483−317 Scientific Reasoning Rubber bands can be stretched and return to original shape when the stretch is released. In the experiment, as the rubber band is pulled back, a transfer of energy occurs from the human hand exerting the force (the stretch) to the rubber band. The amount of energy that is transferred by the human hand is called the work done by that force. The common equation for calculating the work done by the force, is ‘W = F.d’, where W is the work done, F the force applied on a distance ‘d’. This equation demonstrates that the further the pull back, the more energy is transferred to the rubber band. Hooke’s law, F = -kx established that the strain force is proportional to the distance of the stretch within the elastic limit of the rubber band used. These two equations are related and both show that when the pullback length is increased, so is the strain force. As energy is transferred to the rubber band, potential energy is built up and stored in the rubber band. Potential energy reflects a potential to do work, in that case the energy associated with the stretched position of the rubber band. As the rubber band is released, it gets LAB REPORT Tub Experiment Victor Blum, 8C, April, 30 2019 back to its original shape (restoration force) pushing the tub forward and inducing an acceleration. The potential energy starts transforming into kinetic energy ( law of energy conservation). The kinetic energy is the energy of motion, associated with the object's motion. For a given stretch, the potential energy is at its maximum when the kinetic energy is equal to zero (elastic band stretched position). As the rubber band is released, the potential energy is gradually converted into Kinetic energy. The tub will eventually stop due to the frictional force caused by the floor. The formula for Potential energy is PE = ½ kx² where ‘k’ is the spring constant and ‘x’ the length of the stretch. The formula for kinetic energy is ‘KE = ½ mv², where m is the mass of the tub and v its acceleration. They demonstrate that the longer the stretch of the band is, the greater the energy is transferred and therefore the greater travel distance is achieved by the propelled tub. Validity of Hypothesis My hypothesis is validated because the further I pull back, the more the distance is covered by the tub (Table 3 and Graph 1). But I did three trials for each pull back distance, a total of 15 pull backs in all my experiment. I further noticed that although the tub is covering more distance, the pattern of distance travelled, with every 10 centimeter increase inthe pull back is not constant. Table 4 shows how from the first trial (15 cm pull back) all the way to the last trial (55 cm pullback) the difference in the average distance by tub in between interval (15, 25, 35, 45, 55) is not uniform. Although there is a change is the distance travelled by the tub, but the percentage is in fact decreasing at 15 cm, it was at a 100 %, but when the pull back distance wasa changed to 25 (10 cm more), the difference in distances is 119 and the percentage change is 60.1. With the change again, to 25 cm, the change is 52.4%. For 45 cm, the change is 43.9 % and finally, for 55cm, the change is 25.6%, and if i continue to stretch my pullback distance, the distance covered by the tub may not increase since the elasticity of the rubber band is reduced Validity of Method I took every precaution during my experiment, from making sure that the chair was sturdy and all four legs intact. Also ensuring that the ground was flat and that there were no obstacles in the way. When measuring the pull back distance or calculating the distance travelled by the tub. Making sure the tub was not tampered. The rubber bands were identical. When I was conducting my experiment, I made sure there were not external disturbances that would affect the chair or the floor. Improving the Investigation and/or Further Inquiry If I was to do this experiment again, I would change the rubber bands for every new pullback distance so I can have much more reliable results. As for this investigation, is did not change it and used it 15 times and that might prove a slight change to the result would have gotten if I had used a new set of rubber bands for each trial. For the rest I made sure my experiment and the procedure all went well. Precautions: LAB REPORT Tub Experiment Victor Blum, 8C, April, 30 2019 - Don’t shoot people with the rubber bands Ensure that passage is clear before shooting the tub LAB REPORT Tub Experiment Victor Blum, 8C, April, 30 2019 Works Cited The Editors of Encyclopaedia Britannica. "Hooke's law." Britannica, www.britannica.com/science/Hookes-law. Accessed 29 Apr. 2019. "Physics of a Slingshot." Youtube, uploaded by Mark Von Bokern, 25 Nov. 2017, www.youtube.com/watch?v=8zQknQlNfDU. Accessed 29 Apr. 2019. "The Physics of Slingshots 2 | Smarter Every Day 57." Youtube, uploaded by Smarter Every Day, 19 July 2012, www.youtube.com/watch?v=1v4TEX2erog. Accessed 29 Apr. 2019. "Potential energy stored in a spring." Khan Academy, uploaded by Sal Khan, www.khanacademy.org/science/ap-physics-1/ap-work-and-energy/spring-potentialenergy-and-hookes-law-ap/v/potential-energy-stored-in-a-spring. Accessed 29 Apr. 2019. "Potential energy stored in a spring." Khan Academy, uploaded by Sal Khan, www.khanacademy.org/science/ap-physics-1/ap-work-and-energy/spring-potentialenergy-and-hookes-law-ap/v/intro-to-springs-and-hooke-s-law. Accessed 29 Apr. 2019. LAB REPORT Tub Experiment Victor Blum, 8C, April, 30 2019 "slingshot physics." Youtube, uploaded by Keith Grissom, 2 May 2013, www.youtube.com/watch?v=Qv0mSkeVCAI. Accessed 29 Apr. 2019. "What is Hooke's Law?" Khan Academy, www.khanacademy.org/science/physics/workand-energy/hookes-law/a/what-is-hookes-law. Accessed 29 Apr. 2019.
