Understanding Acceleration From Different Frames of Reference

[Sean1218]

This is what my teacher told me, but I still don't really see how it works.

Say a person is in a car traveling at constant velocity, and it crashes into a tree, from an inertial frame of reference (the road), the person in the car continues traveling at the constant velocity of the car until he hits the dashboard. However, from the non-inertial frame of reference of the car, the person is at rest, and suddenly starts accelerating until he hits the velocity of the car, at which point he continues moving at that constant velocity (or until he hits the dashboard).

and you can even calculate this acceleration if you know how long it takes since you have v1 (from rest), and v2 (velocity that the car had). What I don't get is that if from the frame of reference of the car, if he's accelerating for a brief moment, and you can actually calculate it, how could someone on the road not see this acceleration?

or is it not a smooth acceleration? like, is it he's at rest, then as soon as the car hits the tree, he's at constant velocity? and that's why he's saying he's accelerating? but in this case there's no time between the two to calculate...

So, if you have two people staring at this guy in the car crashing into the tree, one is in the car, and one is on the road, the guy on the road will see the guy in the car continue moving at constant velocity as the car hits the tree, while the guy in the car will see the other guy in the car accelerating from rest to the constant velocity of the car (or until he hits the dashboard)?

Could anyone help clear this up for me?

 

[kuruman]

This is what my teacher told me, but I still don't really see how it works.

Say a person is in a car traveling at constant velocity, and it crashes into a tree, from an inertial frame of reference (the road), the person in the car continues traveling at the constant velocity of the car until he hits the dashboard. However, from the non-inertial frame of reference of the car, the person is at rest, and suddenly starts accelerating until he hits the velocity of the car, at which point he continues moving at that constant velocity (or until he hits the dashboard).

and you can even calculate this acceleration if you know how long it takes since you have v1 (from rest), and v2 (velocity that the car had). What I don't get is that if from the frame of reference of the car, if he's accelerating for a brief moment, and you can actually calculate it, how could someone on the road not see this acceleration?

Someone on the road will see the car's acceleration, but not the driver's acceleration. The driver will be seen as moving at the velocity of the car until he hits the dashboard.

or is it not a smooth acceleration?

I am not sure what you mean by smooth.

like, is it he's at rest, then as soon as the car hits the tree, he's at constant velocity?

He is at rest or at constant velocity with respect to what?

So, if you have two people staring at this guy in the car crashing into the tree, one is in the car, and one is on the road, the guy on the road will see the guy in the car continue moving at constant velocity as the car hits the tree, while the guy in the car will see the other guy in the car accelerating from rest to the constant velocity of the car (or until he hits the dashboard)?

Could anyone help clear this up for me?

The passenger in the car will be at rest with respect to the driver, and will suffer the same fate as the driver. That's for sure, unless one has his seat belt fastened and the other has not.