gravity by freefall

ublinia2

For g by freefall - ie experiment to measure the acceleration due to gravity by timing the time it takes for a ball baring to fall a certain distance. What effect does:

1. a change in atmospheric pressure in the experiments environment
2. a change in temperature in the environment

have on the experiment , the fall of the ball and the value of gravity obtained from the experiment?

Delphi91

ublinia2 wrote:

For g by freefall - ie experiment to measure the acceleration due to gravity by timing the time it takes for a ball baring to fall a certain distance. What effect does:

1. a change in atmospheric pressure in the experiments environment
2. a change in temperature in the environment

have on the experiment , the fall of the ball and the value of gravity obtained from the experiment?

None.

Think of the equation that you use for the experiment:

s = ut + 1/2gt^2

None of the variables you've mentioned are included in the equation.

Mike

Son Goku

ublinia2 wrote:

For g by freefall - ie experiment to measure the acceleration due to gravity by timing the time it takes for a ball baring to fall a certain distance. What effect does:

1. a change in atmospheric pressure in the experiments environment
2. a change in temperature in the environment

have on the experiment , the fall of the ball and the value of gravity obtained from the experiment?

Very, very little.

In fact the main effect air pressure has on free fall has nothing to do with the pressure itself but an effect from the Bernoulli equation where greater air pressure will give a slight spin to the object.

However, overall the effects are almost negligible.

dudara

I suspect that variables such as pressure and temperature would only come into play if the ball-bearing was falling over an appreciable height, such as a couple of hundred metres or more. In that case, air resistance and terminal velcity would be playing a part anyway.

So for normal lab situations, they wouldn't matter, and you stick to s = u*t + (1/2)*a*t^2

ublinia2

Son Goku wrote:

Very, very little.

In fact the main effect air pressure has on free fall has nothing to do with the pressure itself but an effect from the Bernoulli equation where greater air pressure will give a slight spin to the object.

However, overall the effects are almost negligible.

Can you refresh me on the Bernoulli equation ?The fact that the ball is spinning wouldnt really have any effect on the ball.

At what pressure would the laboratory conditions need to be at for an effect to take place ?

Say the ball fell over a very large distance ( in theory )( and just ignoring terminal velocity etc ) - how would a diffference in pressure impact on this now?

~can I find a percentage difference between two values for g , say one which i measure in the lab and pressure is 100 Pa and I do the same experiment again with the pressure at 150 Pa , what would be my percentage error or difference from one reading to the next ? ie how would I begin to show this difference mathimatically?

ublinia2

If the temperature of the lab increases, at what point could it have an impact on the speed the ball falls ?

i.e. say in theory , i set up the experiment at 0 degrees celcius ( in theory and in lab conditions ) and get a value for g and time of ball fall.

Then I set up the exact same the conditions again with say temperature at 300c ( in theory ) , how would I calculate the percentage difference in the two now ?


The value might be so small over the distance that I have in the lab , but say the distance was very large ( and ignoring terminal velocity of the ball ), what impact would the above changes in temperatures have on the results?

ghostchant

ublinia2 wrote:

Can you refresh me on the Bernoulli equation ?The fact that the ball is spinning wouldnt really have any effect on the ball.

It wouldn't really have an effect in this case, but neither would the air temperature.
The fact that the ball is spinning would change it's trajectory over distances a bit longer - like when you apply topspin to a tennis ball - different parts of the ball would have different velocites.

Capt'n Midnight

you could use ball bearings of different sizes and compare them

google "stokes law"

AlienGav

It wouldn't really have an effect in this case, but neither would the air temperature.

Wouldn't the various tempratures play a part in the air's viscosity?:eek:
Cold conditions would make the air more viscous, and therefor create a larger force acting against the ball bearing's fall.
Warm conditions - gentle air viscosity, as the air's molecules would not be so closely packed together, therfor slightly quicker descent for the ball bearing!

Capt'n Midnight

AlienGav wrote:

Wouldn't the various tempratures play a part in the air's viscosity?:eek: /QUOTE]not to mention the amount of water vapour in the air. And you would also have to do the expirement in a climate controlled chamber with baffles to stop any horizontal or vertical movement of air. Oh and a barometer to see how dense the air is along the track of the object.

ghostchant

AlienGav wrote:

Wouldn't the various tempratures play a part in the air's viscosity?:eek:
Cold conditions would make the air more viscous, and therefor create a larger force acting against the ball bearing's fall.
Warm conditions - gentle air viscosity, as the air's molecules would not be so closely packed together, therfor slightly quicker descent for the ball bearing!

'Slightly' is certainly the word
But in this experiment the ball bearing is only falling a very small distance, and the air temperature isn't really going to affect what happens.

Though to be honest I'm flying blind here I can't say I've given this much thought.