# Candle in a lift

1. Dec 9, 2006

### joker_900

How would a lift accelerating upwards affect the shape of the flame of a candle in it? My instinct says it would flatten it, but I'm not sure how to explain why. Any help?

2. Dec 9, 2006

### Danger

Consider that the flame is lighter than air. How would a helium balloon react under the same circumstances?

3. Dec 9, 2006

### joker_900

Hmm well in a normal situation the balloon rises because the upthrust (due to pressure difference) is greater than its weight and so pushes it to a less dense region. So when the lift accelerates upwards, i guess the normal air, being more massive, has greater inertia so tends to be denser at the bottom? Therefore pushing the balloon upwards even more?

So would the flame get taller then?

4. Dec 9, 2006

### chandubaba

In my opinion (if air does not extinguish the candle)the flame of the candle MIGHT get flattened but it will ignite more than at constant velocity or at rest, because of inertia.The flame would tend to move downwards because of inertia which means more of the chemical substance of the candle would get melted so more fuel for ignition.

5. Dec 9, 2006

### tehno

Supposing the elevator is closed box,the pressure of air will change (if the elevator is accelerating).
Under these circumstances it is sufficient to consider the change in candle flame just as caused by change of an atmospheric pressure.

6. Dec 9, 2006

### marlon

Indeed, that's a very good hint.

Another classic is this : consider a Helium balloon on a rope. As you are sitting in a car, you hold the rope (to be clear : the balloon rises and finds a position at the ceiling of the car and the car accelerates foreward. What will happen to the balloon ? Does it remain fixed in its position, does it move foreward (same direction as the acceleration), does it move backward etc etc ???

marlon

7. Dec 11, 2006

### student85

Hmmm
What happens to the flame in the candle then??

Does it flatten, being the explanation that its inertia wants to keep it from accelerating?
How does it relate to the balloon scenario???

8. Dec 12, 2006

### enricfemi

In my personal sense,if the lift is airproof,the flame will not easily been seem to flat.if you found it flat,it doesnot matter with accelerate,it does matter with the v of air

9. Dec 12, 2006

### Q_Goest

I like Danger's hint too.

The best visualization I've heard is to imagine the air as a fluid that 'sloshes around'. As the lift accelerates upwards, the air sloshes to the bottom, making the flame taller and thinner. As the lift accelerates downwards, the air sloshes to the top, making the flame shorter and flatter.