# Nonexistent force

1. Dec 7, 2005

### Robokapp

I don't know if this was already adressed, but I saw in my book the term of Non-existent force and until today I didn't get what it is referring to...why it's non-existent.

Assuming you're in a car with linear motion, constant velocity...zero acceleration. You hit your break as hard as you can. You will be pushed forward and collide with the steering weel.

Question: Where do you get the force that leads to you moving in report to the steering weel if you were at equilibrium with the rest of the car and the brake affects the car, not you?

The 5-step process and Newton's 3 laws make no mention of this. The more i'm trying to apply them the more i feel like an idiot.

Any help? Some info...whatever?

2. Dec 7, 2005

### Fermat

Centrifugal force is a called both a ficticious force and a non-existant force.
When travelling in a circle, there is a centriptal force on your body directed towards the centre of rotation. Centripetal force is an actual, real force.

Centrifugal force is suppposed to be numerically equal to centripetal force but acting in the exact opposite direction, radially outwards. Not so. There is no force pusing you out, that is an inertial effect!

Centrifugal force is still used though, in astrophysics or something like that - it makes it easier to visualise things perhaps - I'm not sure exactly.

When travelling in a circle, your body will naturally want to travel in a straight line. If a centripetal force pushed you radially inwards, then the inertia of your body, which will make it want to travel in a straight line, will "push" outwards. That is the inertial effect. The inertia of your body trying to resist an accelerating force.

When the car crashes, you are not pushed forwards, rather it is the car that is being pushed backwards. The inertia of your body wants it to continue in a straight line - forwards - and so "pushes" against the car steering wheel as it very quickly slows down (decelerates).