Collisions

[object Object],The force from the seatbelt safely decelerates the driver, but the child in the back seat follows Newton's Law of Inertia and continues moving in the absence of a net force. The 60mph "kid" not only breaks its own neck but also the neck of the driver.

[object Object],It should be pointed out that the rotating dial makes 1 rotation in 1/10th of a second. It was used to measure small intervals of time on the film (pre-digital clock)

[object Object],They were at rest originally, and in the absence of a net force (from the seat belt) they remained at rest while the car they were in was accelerated by the net force from the car that hit them. Newton's first law can be a killer! In this clip, the station wagon literally gets accelerated out from under the "kids" sitting in the back.

[object Object],The only way it slows the occupants more gradually is if they are attached to the car. Otherwise, the car may come to rest more slowly but the people come to rest immediately upon striking the already stopped interior of the car. Stopping in a small amount of time means the force must be very large. This video clip shows some very dramatic scenes of car crash tests with test dummies who are not wearing seat belts. Specifically look for cars crumpling and people stopping in very small amounts of time.

[object Object],This keeps the force required to stop them smaller. (see impulse) It also prevents the person from contacting any of the glass windows in the car or continuing on to be stopped abruptly by the road, tree, or another automobile. The video clip above shows the role of the seatbelt during an accident.

Momentum Conservation Principle ,[object Object],[object Object],[object Object],[object Object]

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Vector Representation of Conservation of Momentum

Practice! ,[object Object],[object Object]

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Collisions

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Collisions