Crumple Zones - Physics

Name: Date: Student Exploration: Crumple Zones Directions: Follow the instructions to go through the simulation. Respond to the questions and prompts in the orange boxes. Vocabulary: acceleration, airbag, collision avoidance system, crash test dummy, crumple zone, force, kinetic energy, Newton’s laws of motion, safety cell, seat belt, work, work-energy theorem Prior Knowledge Questions (Do these BEFORE using the Gizmo.) Two burglars run down an alley at night, trying to escape the cops. Jack is carrying a rigid metal safe. Jill is carrying an armful of antique quilts. In the pitch dark, they both collide headlong into a concrete wall. 1. Who do you think will be hurt more in the collision, and why? jack because he has something heavy that’s not easily crushed 2. During a car crash, what features of the car might act like either Jack’s safe or Jill’s quilts? The quilts will act as an air bag and the safe would act like the metal cage of the car Gizmo Warm-up When cars were first invented, the safety of passengers was not a great concern. As vehicles grew larger and faster, accidents became more deadly. Safety features went from being a rare luxury to a legal requirement. In the Crumple Zones Gizmo, you will design cars that will help a crash test dummy survive a collision. 1. To begin, do not make any changes to the DESIGN tab of the Gizmo. Select the CRASH TEST tab, and click Play ( ). After the crash, click Slo-mo replay. What happens? The test dummy launches forward and the car gets crushed 2. Select the RESULTS tab to read about the results of the crash. Do you think a passenger would have survived this car crash? Explain. No because there was severe trauma to the head with the torso Get the Gizmo ready: Activity A: ● Click Reset ( ). ● On the DESIGN tab, check that Sedan is selected. Surviving a crash Introduction: Modern vehicles contain features designed to keep passengers safe in a crash. The crumple zone in the front of the car slows the car gradually and increases stopping time. The safety cell is a rigid cage that prevents passengers from being crushed. Inside, seat belts and airbags prevent the driver from hitting the windshield, steering wheel, or dashboard. Question: How does a crumple zone help protect a passenger? 1. Make a hypothesis: On the DESIGN tab, look at the parameters you can control. What settings do you think will make the safest car? Set up the Gizmo, and then fill in below. Crumple zone length: 120 Crumple zone rigidity: 100 Safety cell rigidity: Seat belt present? yes If present, seat belt stiffness: 54 Air bag present? yes If present, air bag rigidity: 50 4,000 2. Test: On the CRASH TEST tab, check that the Car 1 speed is 16 m/s, or about 35 miles per hour (mph). Click Play. After the crash, select the RESULTS tab. A. By what percentage did the crumple zone deform? 1.2 B. Did the dummy hit the steering wheel? no C. What was the maximum force on the dummy? 17.01N D. How likely was the dummy to survive? 95% Safety cell? 0.05 In this simulation, forces are measured in kilonewtons (kN). One kilonewton is equal to 1000 newtons, or the force of a 225-pound (102 kg) person standing on your chest. While many factors affect survival, only the maximum force and safety cell collapse are considered here. 3. Experiment: On the DESIGN tab, set the Crumple zone length to 100 cm and the Safety cell rigidity to 2000 kN. Set the Seat belt stiffness to 50 kN/m and turn off the Airbag. For each Crumple zone rigidity setting, run a 16 m/s crash test and enter the results below. Crumple zone rigidity 100 kN 200 kN 300 kN 400 kN Crumple zone deformation 1m 0.93m 0.62m 0.47m Dummy displacement 1.42m 1.21m 1.02m 0.93m Max. force on dummy 20.88kn 14.25kn 19.88kn 23.02kn Likelihood of survival 87% 100% 89% 82% 4. Evaluate: Look at the results of your experiment. What was the relationship between crumple zone rigidity, crumple zone deformation, and maximum force on the dummy? The rigidity and deformation helps reduce initial force for they dummy 5. Infer: For a 1.00 m (100 cm) crumple zone, how much deformation do you think is needed in order to keep the passenger the safest? 200 kn Explain your answer: the dummy gave a 100% survival rate 6. Explore: In the U.S., all cars are evaluated using a frontal 35 mph (~16 m/s) crash test. Using the variables on the DESIGN tab, try to design a car that produces the lowest possible force on the dummy and does not injure the dummy in a 16 m/s crash. If you like, record your data on the provided blank data tables on the next page. When you have finished, describe your car and your results below. Car parameters (CZ = crumple zone, SC = safety cell, SB = seat belt, AB = airbag) CZ length 120 CZ rigidity 100 SC rigidity 4000 SB stiffness 54 AB rigidity 50 SC deform. Dummy disp. Max. force Survival % Crash results CZ deform. 7. Test: Click Reset. On the CRASH TEST tab, change the Car 1 speed to 22 m/s (about 50 mph). Run a crash test at this speed, then look at the summary data. A. What did you find? everything increased but the crumple zone deformation. Along with a 0% survival rate. B. What is a possible disadvantage of designing a car for only one crash speed? some areas have higher speed limits than other ones Blank data tables for car experiments (make as many copies as you need) Key CZL = Crumple zone length (cm) CAR = Crumple zone rigidity (kN) SCR = Safety cell rigidity (kN) SBS = Seat belt stiffness (kN/m) ABR = Air bag rigidity (kN) CZ def = Crumple zone deformation (m) SC def = Safety cell deformation (m) Dum d = Dummy displacement (m) Max F = Maximum force on dummy (kN) Surv% = Likelihood of survival CZL 120 85 60 55 85 75 65 100 70 85 Car parameters CZR SCR SBS 100 4000 54 1300 2900 92 3600 1950 63 2700 2450 55 2200 3200 38 4000 4000 50 2800 2950 55 4000 3200 47 2700 2050 52 3500 2850 59 ABR 50 27 34 30 23 29 32 25 32 36 CZ def 1.2 .14 .05 .07 .09 .05 .07 .05 .07 .05 Crash results SC def Dum d Max F 0.05 1.52 17.01 .06 0.47 57.12 .1 0.44 58.46 .08 0.47 52.06 .06 0.55 39.2 .05 0.49 50.99 .06 0.47 54.32 .06 0.49 45.55 .09 0.47 52.58 .07 0.46 59.79 Surv% 95% 0% 0% 0% 32% 0% 0% 0% 0% 0% CZL 60 120 120 120 Car parameters CZR SCR SBS 2600 1650 75 4000 4000 100 3200 3200 55 2200 2750 50 ABR 26 50 30 27 CZ def .07 .05 .06 .09 Crash results SC def Dum d Max F .11 .43 52.79 .05 .4 83.41 .06 .47 52.82 .07 .5 47.31 Surv% 0% 0% 0% 0% Activity B: Get the Gizmo ready: Modern safety features ● Click Reset. ● On the DESIGN tab, check that Sedan is selected. Introduction: The idea of a crumple zone was conceived by Béla Barényi in 1952 and first used in the 1959 Mercedes W111. Seat belts were also first widely used in the late 1950s. More recently, airbags and collision avoidance systems (CAS) were introduced. Question: How do modern safety features and body types help keep passengers safe? 1. Experiment: Set the Crumple zone length to 90 cm, the Crumple zone rigidity to 1000 kN, and the Safety cell rigidity to 1000 kN. Turn off the seat belt and the airbag. These settings represent a 1950’s car with no crumple zone, seat belt, or airbag. A. On the CRASH TEST tab, set the Car 1 speed to 16 m/s. Click Play. What happened to the dummy? no chance of survival B. Turn on the seat belt and set the Seat belt stiffness to 100 kN/s. Run another crash. What What happened? no injury because of the seatbelt C. Set the Crumple zone rigidity to 250 kN and run another test. What happened? The survival rate was 95% dummy wasn’t injured D. How did the crumple zone and seat belt work together to keep the driver safe? less impact because the seatbelt helps keep the dummy in place instead of letting it fly straight out 2. Test: An airbag is designed to quickly inflate on impact, then deflate as the passenger hits the bag. Invented in the early 1970s, airbags did not become widespread until the 1990s. Using the crumple zone and safety cell settings above, experiment with the seat belt to find the lowest possible force on the dummy. Then, experiment with just the airbag. Finally, include both the seat belt and airbag. Report your findings below. Setup Seat belt only Airbag only Seat belt and airbag Seat belt stiffness 100 (No seatbelt) 100 Airbag rigidity (No airbag) 5 5 How did the seat belt and airbag work together to keep the driver safe? Max. force 16.55 KN 1000 KN 20.36 KN It helps keep the driver from flying out and having a less hard impact. 3. Experiment: Another modern safety innovation is the collision avoidance system, or CAS. A CAS will apply the brakes when it senses an imminent collision. The brakes can slow the car by about 8.8 m/s for each second they are engaged. Click Reset. On the CRASH TEST tab, select Enable collision avoidance system (CAS). Drag the car to the far right of the track at the bottom of the Gizmo, then click Play. What were the results of this test? 100% survival rate. the car didn't hit the wall. 4. Explore: Click Reset. In some cases, there will not be enough time for the car to completely stop before the crash occurs. However, the CAS can still be useful. On the CRASH TEST tab, set the Car 1 speed to 23 m/s (about 50 mph). Play a crash without the CAS, and then run another test with the CAS on. What did you find? it takes longer for the car to stop 5. Challenge: You work in the safety engineering department for a large auto manufacturer. Your job is to create the safest possible vehicle given each of the following design criteria. Using the Gizmo, try to create a vehicle that meets each description. ● ● ● Design the safest possible SUV with a crumple zone length of 85 cm, no CAS, and a speed of 20 m/s (45 mph). (Note: Injuries such as broken legs are not allowed.) CZL CZR SCR SBS ABR Max. F Surv% 85 cm 2700 2500 91 0 31.47 60% Design the safest possible subcompact (no injuries) with a crumple zone length of 80 cm, no CAS, and a speed of 18 m/s (40 mph). CZL CZR SCR SBS ABR Max. F Surv% 80 cm 750 2050 76 0 30.84% 62% Design a sedan with a crumple zone length of 110 cm that can give passengers a greater than 50% chance of surviving a 27 m/s (60 mph) crash and give passengers a greater than 80% chance of surviving a 16 m/s (36 mph) crash. (Note: Crumple zone length in both experiments is 110 cm.) Speed CZR SCR SBS ABR 27 m/s 16 m/s 500 550 100 0 Max. F Surv% 21.65 65% 21.65 85%