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CRASH TEST DUMMY
------ I nteractive Physics Simulation - ------
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How can you best protect yourself in an automobile accident?
The goal in any collision is to bring you from high speed to low speed as safely as possible. It takes a lot of force to slow you down. Let's reduce the force by deploying an airbag. Collision safety systems try to extend the amount of time it takes to slow you down to stop. The area bounded by a force vs. time graph is equal to the impulse applied to you. The impulse, in turn, represents the change in momentum you experience. To accomplish the same goal, you can apply a big force for a short time, or small force for a long time.
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Velocity of car - T his slider determines the velocity of the car before it collides with the wall. The velocity is negative because the direction is leftward. The change in velocity, therefore, is positive.
Type of restraint - This slider determines the type of restraint available to the dummy. This, in turn, determines the length of time over which the force is applied to the dummy. By increasing the time, you'll see that the force applied is less - this is safer for the passenger.
Mass of dummy - T his slider determines the amount of inertia the dummy has in the collision. A higher mass will require more force to bring it to a stop.
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Momentum Bar Graph - T his kind of graph is known as a momentum bar graph. The height of a given bar is determined by the velocity of the dummy. Negative velocities are leftward, positive velocities are rightward. The width of a given bar is determined by the mass. Since momentum is the product of mass and velocity, the AREA of the bar tells us about the momentum of the system. Three bars are provided: BEFORE the collision, AFTER the collision, and the CHANGE DUE TO the collision.
Force vs. Time - T his is an idealized plot of the force experienced by the dummy as it comes to a stop. The force is applied to it by the restraint (seat belt, air bag) or, if there is no restraint, by the steering wheel or front window. Different restraints act to lengthen the time of the collision, reducing the overall force. Your task will be to find a relationship between the area of this graph and the change in momentum of the dummy, which you can see in the left-hand graph.
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Set up a situation where the impulse delivered is 1800 N-s and the maximum force felt by the dummy is 25000 N. ( Adjust the sliders to achieve the conditions described.)
For a 30 m/s collision with a 70 kg dummy, what type of restraint will cause the impulse to the dummy to be experienced over the greatest amount of time? (Set the velocity slider to -30 m/s and the mass of the dummy to 70 kg. For which restraint will the dummy feel a force over the longest amount of time?)
Under what conditions is the maximum force experienced by the crash-test dummy highest? (Adjust the sliders so that the force experienced by the crash-test dummy is as high as possible.)
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Challenge ME!
The momentum of the system is equal to the mass times the velocity. What is the largest initial momentum that simulation allows and what is the smallest?
What type of collision produces the highest peak force? What about the smallest peak force?
The area of the graph on the right is known as the impulse delivered to the dummy. Estimate this area, does it change when the type of restraint is changed? Why or why not?
How does the area of the graph on the right (the impulse) compare to the change in momentum experienced by the dummy?
Need Help?
Check out the Crash Test Dummy Walkthrough video at: h ttps://youtu.be/gfoy0DF9RQY
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What is the best strategy to win an “egg-toss” competition? It is usually a good idea to avoid applying big forces to an egg. So, the best strategy is to increase the amount of time you spend slowing the egg down. One great way to do this is to allow the egg to slowly come to a stop by reaching your hand out and swinging backward as the egg comes to a stop.
You are running towards second base, how can you avoid overrunning the base? Your goal is to stop on the base. The problem is, if you are running quickly, and you try to stop quickly, you need to apply a great force with your feet, and you might slip. If, instead, you slide into base, you experience a smaller force over a longer period.
Why were the hammer and nail invented ? When you strike a nail with a hammer, the hammer head has a lot of momentum before the collision. A large, brief upward force on the hammer, applied by the nail, brings the hammer to a stop. The third-law pair force acts downward on the nail and is equally large and brief. This huge force allows the nail to split the wood and sink in.
Why does a car “peel-out”? In order to accelerate very quickly from a stop, your tires need to apply a very strong force to the road. This force might exceed the “slipping threshold” that depends on the roughness of your tires and the road surface. If, instead, you accelerate over a longer period of time, less force is required, and you are less likely to exceed the slipping threshold.
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Physics Concepts | C lick on the link below to learn more.
Impulse - h ttp://www.ck12.org/physics/Impulse/
Momentum - http://www.ck12.org/physics/Momentum/
Momentum and Impulse - h ttp://www.ck12.org/physics/Momentum-and-Impulse/
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