Momentum Assignment PDF

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Essay I wrote about seatbelts relating to momentum for Grade 12 Academic/University Physics. We had to write an essay about a modern device that involved momentum and explain how it worked. ...

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The Effects of Seatbelts Involving Momentum and Force

SPH4U1-1 Mr. April 1, 2019

2 Seatbelts and Car Accidents The seatbelt is a passive vehicle safety feature made to decrease the severity of injuries people receive during a car crash (Seatbelts, n.d). Seatbelts hold a person’s body in place during a car accident (Caliber Collision, n.d). They are able to stretch slightly if they experience a large force, such as the force created in a car crash (Seat belts are life savers, n.d). When someone is sitting in a vehicle, they and their vehicle are two separate objects moving in the same direction, at the same speed, through space. For example, if someone is in a car driving at a velocity of 70 MPH, that means that both the car and their body are two separate objects moving at a velocity of 70 MPH through space. When a vehicle hits another object, it will stop, however, the person inside the vehicle will continue to move forward at the velocity they were travelling at before the car crashed, due to inertia, with a considerable momentum, until another object stops them. (Glenn, 2017) Newton’s first law of motion states that an object in motion or at rest will stay in motion or at rest, with a constant velocity, until an external net force acts on it (NEWTON, CARS AND CAR SAFETY, n.d). Thus, a car accident will not stop the forward momentum of one’s body, which could result in a person flying forward until they collide with a part of the car which would then change their momentum to zero and stop them, such as the windshield, if they are not restrained by a seatbelt (Caliber Collision, n.d). If the momentum of a person in a car crash changes this rapidly in a short period of time, they would experience an enormous force from the crash exerted onto their body which would likely kill them. If the momentum can be changed over a longer period of time by using a restraining device such as a seatbelt, less force would be applied to the person in the car, resulting in less damage to their body.

3 This can be shown using the equations for both momentum (Δp) and impulse: Δp = FΔt As time increases, the force will decrease.

How a Seatbelt Works Seatbelts are made to stretch slightly when a car decelerates quickly, which increases the time in which a person’s momentum is changed during a car crash, thus, decreasing the force exerted onto their body. The stretch in a seatbelt allows for a person to come to a stop over a shorter distance, allowing their momentum to be reduced gradually, meaning that the seatbelt would exert less of a force on the person than the windshield would if the person flew into it, due to not wearing a seatbelt. The restraining force of the seatbelt acting over a longer period of time is able to reduce the amount of force needed to change the momentum of a person during a car crash. (Seat belts are life savers, n.d) This stretch in the seat belt lengthens the time that the person wearing it is able to decelerate during a car crash, which greatly reduces the impact force of the crash on a person (Shiu-sing, n.d). A seatbelt allows one to have a stopping or deceleration distance that is four to five times greater than if a person was not wearing a seatbelt, during a car crash (Glenn, 2017). By using a seatbelt, a person is no longer a separate object from the car anymore and instead, the forces caused by a car crashing are spread through the seatbelt, meaning that the person’s momentum is absorbed by the car instead of the windshield. A seatbelt’s straps also spread over a large area of the body which spreads out the impact force absorbed by the body from the car crash to more durable parts of the body, which prevents the force from doing as much damage (Glenn, 2017). During a car crash while a person is wearing a three-point “Y” seatbelt, the seatbelt disperses the momentum into the person’s chest, shoulders,

4 and pelvis. This means that people are much less likely to die or get seriously injured in a car accident, if they are wearing a seatbelt. This reduced change of critical injury can ultimately reduce the potential healthcare costs of a person involved in a car crash. Seat belts can also lower one’s car insurance premiums and wearing a seatbelt can ensure that one is not at risk for receiving a seat belt ticket. Seatbelts have been proven to be extremely effective in reducing the amount of fatal injuries caused by car crashes. Someone sitting in the front seat of a car that gets in an accident and who is wearing a seatbelt, has a decreased risk of suffering a fatal injury by 45% and has a decreased risk of a moderate to critical injury by 50% (Caliber Collision, n.d).

Car Crashes with and without a Seatbelt (Non-stretching seatbelt, n.d).

Problems Associated with Other Seatbelt Designs Not all vehicles contain a three-point “Y” seatbelt. Many old designs of cars and current designs of planes use the lap belt style of seatbelt. A lap belt is a seatbelt that consists of one strap covering the pelvic area of a person. The problem with lap belts is that they only disperse a person’s body’s momentum into their pelvic area, causing a greater force to be acting on pelvis which can cause spinal damage or paralysis. The sash belt, a seatbelt consisting of a strap covering one’s abdomen, has also been used in older car models. However, the sash belt proved

5 to be ineffective in the case of a car crash because people could slide forward under the belt. It was determined that the sash belt and lap belt worked best when combined, which is why the majority of car manufacturers now produce cars that only use this seatbelt combination, the three-point “Y” seatbelt (Caliber Collision, n.d)

The Lap Belt Seatbelt (Coalition, n.d).

Recommendations of Future Uses and Innovations Recently, car manufacturers such as Ford have started creating and using inflatable seat belts. How an inflatable seatbelt works is when the vehicle senses a crash, the seatbelt fills with cold, compressed air and expands sideways. This sideways expansion allows for more body area coverage, increasing the area of the body that the stopping force acts on to five times larger than normal seatbelts do. This would ensure that the impact of the force is more widely dispersed, meaning that the person using the seatbelt would face less bodily damage in the event of a car crash. (Glenn, 2017) Hopefully in the future, these types of seatbelts will be manufactured globally and be installed in all cars, ensuring even more safety to those who wear them in the event of a car crash.

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Ford’s Inflatable Seatbelt (Patterson, 2019).

7 References Coalition, T. S. (n.d.). Buckling Up. Retrieved from http://www.800bucklup.org/bucklingup/teens-and-adults.asp Caliber Collision. (n.d.). Retrieved from https://calibercollision.com/hub-of-help/how-does-aseatbelt-protect-you-in-a-car-accident Glenn, A. (2017, April 18). The Physics Behind Seat Belt Safety. Retrieved from https://blog.esurance.com/seat-belt-safety Krisch, J. (2018, June 07). Unfortunately, Your Arm is Not a Seatbelt. Retrieved from https://www.fatherly.com/health-science/seatbelt-car-crash-arms/ NEWTON, CARS AND CAR SAFETY. (n.d.). Retrieved from https://newtoncarsandtheconceptofsafety.weebly.com/seat-belts.html Non-Stretching Seatbelt. (n.d.). Retrieved from http://hyperphysics.phyastr.gsu.edu/hbase/seatb.html Patterson, A. (2019, February 23). Inflatable Seat Belts and Car Seats. Retrieved from https://csftl.org/inflatable-seat-belts-car-seats/ Seatbelts. (n.d.). Retrieved from http://brainonboard.ca/safety_features/passive_safety_features_seatbelts.php#q1 Seat belts are life savers! (n.d.). Retrieved from https://www.cyberphysics.co.uk/topics/forces/seatBelt.html Shiu-sing, T. (n.d.). Retrieved from http://www.hkphy.org/contextual/mechanics/mom/impul05_e.html...