3 ms·

So sum the forces: For Car A: - Force of Car B accelerating Car A opposite to direction of travel - Force of Car B opposing force of Car A trying to accelera

by dools 2y ago

So sum the forces: For Car A: - Force of Car B accelerating Car A opposite to direction of travel - Force of Car B opposing force of Car A trying to accelerate Car B And vice versa for Car B. EDIT: Like if you hit a wall, the wall feels the force of your car. The force that crushes the car is the force opposing that, which is the wall acting on the car. EDIT2 (because I can't reply): the force acting on the driver will be the sum of the force of Car B acting on Car A opposing the force of Car A acting on Car B plus the force of Car B acting on Car A. There are 2 forces in each direction of travel that are exerted by the cars. The force felt by the driver is the sum of these 2 forces, exerted by the dashboard on the driver's face. If the car hits a brick wall, the only force opposing the direction of travel of the car is the force of the wall acting on the car, which opposes the force of the car acting on the wall. As such the force felt by the driver of the dashboard acting on their face is halved. EDIT3 (still because I can’t reply): the dynamics of the materials is not the issue. Yes bricks behave differently than cars, but that’s not the basis of the author’s argument.

chmod775 2y ago
In a perfectly elastic collision between rigid bodies, any impact forces acting on the cars would have to also be transferred to the driver in both instances, but cars are neither perfectly elastic, nor do they behave like rigid bodies in a collision. > EDIT2 (because I can't reply): the force acting on the driver will be the sum of the force of Car B acting on Car A opposing the force of Car A acting on Car B plus the force of Car B acting on Car A. There are 2 forces in each direction of travel that are exerted by the cars. The force felt by the driver is the sum of these 2 forces, exerted by the dashboard on the driver's face. If the car hits a brick wall, the only force opposing the direction of travel of the car is the force of the wall acting on the car, which opposes the force of the car acting on the wall. As such the force felt by the driver of the dashboard acting on their face is halved. If this was how it worked, crumple zones would do nothing. Next you're going to model the airbag as a rigid body too? Ouch.
antod 2y ago
> The force felt by the driver is the sum of these 2 forces Correct me if I'm wrong, but I think you've added non existent extra forces. In the car/car situation, there are still only two forces - each the reaction of the other depending on which cars point of view you're taking. There aren't two separate forces to sum. Each car experiences a decelerating force - the reaction of which is the decelerating force for the other car and the reaction of that is the original deceleration force of the original car.
- dools 2y ago
  If a car crashes into a wall, the wall feels the force of the car and the car feels the force of the wall. If the wall doesn’t move then the force acting on the car is the same as the force of the car on the wall. If the wall is also moving towards the car then the force felt by the car is the sum of the reaction force it would have felt if the wall were stationary plus the force due to the wall trying to accelerate the car in the opposite direction. In the author’s example is says that 2 cars crashing into each other is the equivalent of two cars crashing into a wall, and it’s false.

by dools 2y ago

chmod775 2y ago

In a perfectly elastic collision between rigid bodies, any impact forces acting on the cars would have to also be transferred to the driver in both instances, but cars are neither perfectly elastic, nor do they behave like rigid bodies in a collision. > EDIT2 (because I can't reply): the force acting on the driver will be the sum of the force of Car B acting on Car A opposing the force of Car A acting on Car B plus the force of Car B acting on Car A. There are 2 forces in each direction of travel that are exerted by the cars. The force felt by the driver is the sum of these 2 forces, exerted by the dashboard on the driver's face. If the car hits a brick wall, the only force opposing the direction of travel of the car is the force of the wall acting on the car, which opposes the force of the car acting on the wall. As such the force felt by the driver of the dashboard acting on their face is halved. If this was how it worked, crumple zones would do nothing. Next you're going to model the airbag as a rigid body too? Ouch.

antod 2y ago

> The force felt by the driver is the sum of these 2 forces Correct me if I'm wrong, but I think you've added non existent extra forces. In the car/car situation, there are still only two forces - each the reaction of the other depending on which cars point of view you're taking. There aren't two separate forces to sum. Each car experiences a decelerating force - the reaction of which is the decelerating force for the other car and the reaction of that is the original deceleration force of the original car.

dools 2y ago
If a car crashes into a wall, the wall feels the force of the car and the car feels the force of the wall. If the wall doesn’t move then the force acting on the car is the same as the force of the car on the wall. If the wall is also moving towards the car then the force felt by the car is the sum of the reaction force it would have felt if the wall were stationary plus the force due to the wall trying to accelerate the car in the opposite direction. In the author’s example is says that 2 cars crashing into each other is the equivalent of two cars crashing into a wall, and it’s false.