Speed of a falling raindrop.

durandal01

http://usatoday30.usatoday.com/news/science/wonderquest/2001-12-19-rain-drops.htm

Quote:
"A: It depends on the size and weight of the raindrop how fast it falls: the heavier, the faster."

Is this statement bollocks or am I missing something here?

riffmongous

durandal01 wrote: »

http://usatoday30.usatoday.com/news/science/wonderquest/2001-12-19-rain-drops.htm

Quote:
"A: It depends on the size and weight of the raindrop how fast it falls: the heavier, the faster."

Is this statement bollocks or am I missing something here?

Hm, it looks bollocks alright but it does seem to apply to precipitation. My guess would be that it is not falling faster because it is heavier but a heavier drop is less likely to be affected by updrafts of wind and will appear to be falling faster

FWVT

Why is it bollocks? The explanation given is totally correct. The only time they would fall at the same speed would be in a vacuum.

kona

What the hell does a falling raindrop have to Do with either aviation or aircraft?

Lucena

Maybe because rain can affect how planes fly? Extra weight during a heavy downpour?

The rain in Spain falls mainly on the planes.:P

gdawg87

I always thought things fall at the same speed due to gravity controlling the item. A car falling at the same speed as a bottle of Club orange. But seeing as the car is bigger it would have more air resistance than the bottle, then the club orange would probably hit the ground 1st... I've got it! Try dropping a club orange along with a slightly smaller bottle of coke!

Johnny K

If everything fell at the same speed in air guys jumping out of planes with parachutes would be in a bit of a pickle! Because they fall through a substance called air the large surface area v the mass of the object has effects on the speed something falls. However heavier things do not fall faster just because they are heavier.

EoghanIRL

gdawg87 wrote: »

I always thought things fall at the same speed due to gravity controlling the item. A car falling at the same speed as a bottle of Club orange. But seeing as the car is bigger it would have more air resistance than the bottle, then the club orange would probably hit the ground 1st... I've got it! Try dropping a club orange along with a slightly smaller bottle of coke!

Theoretically yes . On the moon a hammer and a feather dropped at the same time hit the surface of true moon at the same time.

In reality no , weight = mass * force of gravity at x.

A car and a bottle of club orange have different masses and will have different velocities when falling . They won't hit the ground at the same time when dropped from a large space with air resistance present .

I learned that the acceleration of an object is directly proportional to force and inversely proportional to mass. Increasing force tends to increase acceleration while increasing mass tends to decrease acceleration. Thus, the greater force on more massive objects is offset by the inverse influence of greater mass. Subsequently, all objects free fall at the same rate of acceleration, regardless of their mass.

kona

Lucena wrote: »

Maybe because rain can affect how planes fly? Extra weight during a heavy downpour?

Serious ?

mackjark

Well heavier skydivers fall faster. That's why tandem guys have a drogue to slow them down. Even when the parachute opens the lighter you are the slower you fall. Sometimes small women in parachutes seem to float up there for ages.

On the rain point, water drops can go up a well as down particularly in CBs.

On of the weirdest things you'll see in the air is rain just below an aircraft while you remain above it in the clear. It looks like millions of tiny little darts shooting past. When you fly enough you get to see some weird things.

IRLConor

If you're interested in stuff about raindrops this paper has some interesting findings: https://www.irphe.fr/~fragmix/publis/VB2009.pdf

It shows why the maximum diameter of a raindrop is approximately 6mm, among other things.

riffmongous

kona wrote: »

What the hell does a falling raindrop have to Do with either aviation or aircraft?

Not exactly the same but part of the same topic would be the speed of hailstones, which could have an effect on planes

FWVT

EoghanIRL, you're wrong. Any two objects dropped from the same height, h, will accelerate at precisely the same acceleration, g (9.81 m/s/s), until they reach their terminal velocity. The only factor influencing this terminal velocity is wind resistance, which in turn is influenced by the shape of the objects.

Two items of exactly the same mass but different shapes will have different terminal velocities. Likewise, two with different masses could still reach the same terminal velocity if their shapes were different enough, and indeed the lighter object could in fact hit the ground first if it was much more aerodynamic.

This discussion is related to aviation as drag is THE limiting factor when it comes to aircraft performance, and applies to aircraft the same way as it does to raindrops, skydivers, seagull-poop, etc.

Popoutman

FWVT wrote: »

EoghanIRL, you're wrong. Any two objects dropped from the same height, h, will accelerate at precisely the same acceleration, g (9.81 m/s/s), until they reach their terminal velocity. The only factor influencing this terminal velocity is wind resistance, which in turn is influenced by the shape of the objects.

To be pedantic, the retarding force due to the air resistance is present from all non-zero velocities relative to the local airflow, so in effect something that is larger and more dense than another object will be slowed down less by the air resistance - meaning that in an atmosphere the hammer will accelerate faster than the feather towards the ground. The 9.81 value is the maximum acceleration possible in the absence of friction, and this value will also vary depending on local gravity, altitude etc. It does not mean that all objects will accelerate at 9.81 m/s^2. Terminal velocity is reached asymptotically.

FWVT

That's exactly what I said. The hammer will accelerate faster because the force acting on its mass (i.e. its weight) is strong enough to overcome the opposing drag force. In the case of the feather the weight is much less and therefore drag is much more comparable, immediately arresting its fall once released.

If both had the same mass then their weights would be identical, so it would just be a question of how the drag forces compared, as I explained above.

Victor

Won't different sized drops have different shapes as air resistance fights surface tension?

Jimmy444

EoghanIRL wrote: »

Theoretically yes . On the moon a hammer and a feather dropped at the same time hit the surface of true moon at the same time.

You can see it here

Popoutman

FWVT: You stated this:
"Any two objects dropped from the same height, h, will accelerate at precisely the same acceleration, g (9.81 m/s/s), until they reach their terminal velocity. The only factor influencing this terminal velocity is wind resistance"

This was implying that all objects have the same acceleration until terminal velocity is reached - but this isn't the case. The retarding force due to drag means that higher-drag objects (for the same mass/density) will accelerate more slowly from the instant of release, and reaching a lower terminal velocity.

What you said regarding the same acceleration would be true for a vacuum but in that particular case there would no longer be a terminal velocity until impact.