# Fictitious force and accelerating airplane

1. Dec 3, 2007

### hotcommodity

[SOLVED] Fictitious force and accelerating airplane

1. The problem statement, all variables and given/known data

The question asks me to draw a free body diagram for a person standing in an accelerating airplane, and to indicate the fictitious force and any real forces acting on them. The airplane accelerates at 2.22 m/s^2.

3. The attempt at a solution

If the airplane accelerates to the right, I know that the fictitious force (ma) will point horizontally to the left. I know that two other forces will be acting, the normal and weight forces, and that one of them ought to act at an angle. We've been taught that the normal force always acts perpendicularly to a surface, and that the weight force always acts straight downward, so I'm not sure with one will act at an angle and why.

Any help is appreciated.

2. Dec 3, 2007

### PhanthomJay

you forgot the friction force. Without friction, the person won't be standing very long. Unless she's holding on to the overhead luggage racks.

3. Dec 3, 2007

### hotcommodity

You're right I was just thinking that, haha. Any idea on which force acts at an angle tho'?

4. Dec 3, 2007

### PhanthomJay

If the plane is accelerating on a horizontal runway, nothing acts at an angle; if its accelerating at an angle while in flight, as you noted, the weight of the person acts down, the normal force acts at an angle (perpendicular to the floor), friction acts parallel to the floor.

5. Dec 3, 2007

### hotcommodity

So this particular example is not analogous to a mass hanging from a string within the airplane, in which case the tension would act at an angle? The problem goes on to ask what angle a plant would grow at if the plane accelerated long enough....I'm not sure why the problem would give me a value that I couldn't apply...

6. Dec 3, 2007

### PhanthomJay

Oh , that's different. In the first case, assuming accelerating level flight, friction applies
the person's acceleration; in the rope case, it is the horizontal component of the tension that provides the acceleration. Draw a FBD of the plant to identify the angle. (Assume the plant's roots supply the tension force, as if it were supported on a string). Assume level flight, please.

7. Dec 3, 2007

### hotcommodity

Ok, thanks for you help :)