What is Barometer: Definition and 53 Discussions

A barometer is a scientific instrument that is used to measure air pressure in a certain environment. Pressure tendency can forecast short term changes in the weather. Many measurements of air pressure are used within surface weather analysis to help find surface troughs, pressure systems and frontal boundaries.
Barometers and pressure altimeters (the most basic and common type of altimeter) are essentially the same instrument, but used for different purposes. An altimeter is intended to be used at different levels matching the corresponding atmospheric pressure to the altitude, while a barometer is kept at the same level and measures subtle pressure changes caused by weather and elements of weather. The average atmospheric pressure on the earth's surface varies between 940 and 1040 hPa (mbar). The average atmospheric pressure at sea level is 1013 hPa (mbar).

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  1. C

    Pressure in a gas container measured with a barometer and a U pipe

    Can someone please tell me where I am wrong, here goes the question: to a container filled with gas, U shaped pipe is attached, as shown in the picture(picture below). What is a gas pressure in the container if the height of the pillar of mercury in barometer is 740 mm? The way I solved it is...
  2. N

    Weird barometric formula experiment results in Excel

    Hi, as I know the barometric formula is an exponential equation, but when I did the experiment with a barometer at different heights and inserted these results in Excel for curve fitting, it showed a weird thing, I think. So exponential equation did show that R^2=0.942 and the second-degree...
  3. P

    Mercury barometer with a small amount of air

    $$\rho_{Hg} gh_{actual} = \rho_{Hg} gh_{measured} + \rho_{air} gh_{air}$$ Note: by "actual", I mean "theoretical", i.e. what the barometer would measure were there no air inside it. By "measured" I mean "as measured by the faulty barometer, i.e. with some air introduced". I believe this...
  4. Kaushik

    Intuition problem about an accelerating barometer

    Consider a barometer kept in an elevator. When the elevator accelerates upwards, there is a pseudo force along with gravitational force acting on the liquid in the barometer. Due to which pressure on the liquid should increase, right? If pressure on the liquid increases then to balance this, the...
  5. KrimsonTyger

    Is it possible to calculate pressure without a barometer?

    For an experiment, I need to pump air into a rocket with varying volumes of water, and thus air. However, I want to keep the pressure the same. Given the amount of air a bicycle pump can pump, the volume of air already in the rocket, and the desired pressure, is it possible to calculate how many...
  6. J

    Satellite and length of liquid column in a barometer

    Homework Statement Homework EquationsThe Attempt at a Solution Mercury will be in a state of weightlessness in the satellite . The air pressure pushes down on the mercury in the cup as a result of which it rises in the barometer tube . But since it is apparently weightless , it tries to...
  7. I

    Hydrostatics, Length of a mercury column

    Homework Statement What will be the length of mercury column in a barometer tube, when the atmospheric pressure is 75 cm of mercury and the tube is inclined at an angle of 60° with the horizontal direction? Homework Equations Pascal's Law The Attempt at a Solution l ⋅ sinϑ = h l = h / sinϑ l...
  8. M

    Atmospheric Pressure: Solving with a Mercury Barometer

    Homework Statement A mercury barometer located in a room at 25°C has a height of 750 mm. What is the atmospheric pressure in kPa? Homework Equations Patm = ρ*g*H0 The Attempt at a Solution [/B] My question pertains to the units and how it ends up as kPa in the book. I have no problem with...
  9. Plat

    Low Pressure Barometer: Gas Evolution Solutions

    I am working on a barometer that will operate t-ed into an experimental vacuum chamber. The fluid column is composed of vacuum oil so it doesn't boil. I have calculated that given the oil's density of 0.92g/cm3, each cm of oil height indicates 90 pascals of pressure. The oil has a vapor pressure...
  10. Jehannum

    Measuring changes in barometric pressure without a barometer

    Could you use a water u-gauge (manometer), zeroed and with one side of the u-gauge plugged and the other open to air, to show an increase or decrease in barometric pressure after a period of time (e.g. 2 hours)? The idea is that you trap some air at the starting atmospheric pressure on one side...
  11. Dusty912

    Your physics teacher has asked you to build a barometer

    Homework Statement . Your physics teacher has assigned you the task of building a water ba,rometer. You've learned that the pressure of the atmosphere can vary by as much as 5 percent from 1 standard atmosphere as the weather changes. (a) What minimum height must your ba,rometer have? (b) One...
  12. tjvv

    How to detect that my device is underwater?

    Hi, I have a waterproof smartphone with sensors like barometer, gyro, accelerometer, microphone). I want to do an app that 1) detects that the phone is underwater: I though in using some reading from touch panel as water is electro conductive and it may provide me some reading to indicate...
  13. F

    What is the relationship between barometer, pressure, and force?

    Hello Forum, I understand how the Torricelli barometer works. The atmospheric pressure p_0 is balance by the pressure generated by a column of mercury that is 76 cm tall. The shape and diameter of inverted tube containing the mercury does not matter. The size of the container does not matter...
  14. A

    Conceptual question, fluid pressure in a barometer

    Homework Statement I took a stab at the following question in a book: "In one observation, the column in a mercury barometer has a measured height h of 740.35 mm.The tem- perature is -5.0 C, at which temperature the density of mercury r is 1.3608 10^4 kg/m^3 .The free-fall acceleration g at...
  15. CollinsArg

    Vacuum in Torricelli Barometer and it's force?

    Hello! When a torricelli barometer is made there is a vacuum at the end of the top of the tube, does this vacuum exert a force to the water or mercury to go up? and how is that it can be a bigger vacuum depending on the air preassure? How does it exactly work? Thanks.
  16. S

    Barometer Basics: Check Your Homework Answers

    Homework Statement Homework Equations The given ans is 9600 as attached above, but i get 15 000. The Attempt at a Solution
  17. P

    Does the Diameter of a Barometer Tube Affect the Height of the Mercury Column?

    I am curious if the height of the Mercury column inside a Toricellian Mercury Barometer be the same if we use a tapering / stepped (unequal inner diameter [ID]) glass tube as depicted in the image below instead of a regular constant ID one? Note: I know that the ID of a barometer tube does not...
  18. S

    In a barometer, if we replaced the mercury with alcohol and water?

    In a barometer, assuming bernoulie properties(incompressible fluid) if we replaced the mercury with alcohol and water why would the alcohol be able to be displaced further with pressure. It has a lower density that water 800kg/m^3 than water which has 1000kg/m3. What chemical properties or...
  19. C

    How does vacuum form in a barometer?

    Hi, here is something I can't understand: When you fill a 100% tube with Mercury, close it in one end (the top) and stick it into a bowl of mercury, vacuum forms in the top of the tube. Where does the vacuum come from if it was not there to begin with? The tube was full of mercury to begin...
  20. C

    Can adjusting the scale compensate for imperfections in a mercury barometer?

    I have noticed that when I fill the 36 inch glass tube of my mercury barometer, that there are thin bubbles of air stuck between the mercury and the inside wall of the tube; can't seem to get rid of them. Maybe a vacuum needs to be pulled before pouring in the mercury, but that seems...
  21. A

    Barometer Help: Finding Water Column Height with Mercury Column at 32 inches

    Homework Statement Two barometers are made with water and mercury. If the mercury column is 32 in. tall, how tall is the water column? Homework Equations Not sure where to begin with this question. Someone please help! The Attempt at a Solution Need help really bad.
  22. T

    Why doesn't a barometer with vacuum get crushed by the atmosphere?

    Why doesn't a mercury barometer containing vacuum get crushed by the atomospheric pressure? Here is what I think might be the reason. Although there is vacuum inside a mercury barometer, that vacuum is pressurized by the atmosphere that pushes mercury from the reservoir. That pressure is...
  23. B

    How Much Air Is Needed to Lower Mercury in a Barometer from 75cm to 59cm?

    Homework Statement The mercury in a barometer of cross-sectional area 1cm square has a height of 75cm. There is vacuum above it, of length 9cm. What is the volume of air, measured at atmospheric pressure, that would have to be admitted to cause the mercury column to drop to 59cm...
  24. A

    Sensitive barometer indicating altitude

    This is a cry for help. I posted a question under General Physics, titled Sensitive Barometer to Show Altitude on 13 June and have received no replies yet.
  25. A

    Sensitive barometer to show altitude

    I'm having difficulty reproducing an experiment I remember from high school. It's basically a glass bottle with a rubber stopper through which runs a glass tube, bent to form a horizontal portion. A drop of water sits in the horizontal portion. When the external air pressure changes, the air in...
  26. adjacent

    Barometer of Mercury: Weight or Pressure?

    Homework Statement Some websites say that mercury level balances because the weight of the mercury column gets equal to the wight of atmosphere.Is it not the pressure of the mercury column equal to the pressure of the atmosphere. I say this because if the mercury column is wide,the weight of...
  27. D

    Understanding pressure with barometer as example

    In a barometer where a tube filled with mercury is inverted in dish filled with mercury, the mercury in the tube is suspended/rises to 760 mm mark. I read this is due to pressure of weight of mercury being equal to pressure of atmosphere. My question is that, if i were to take the tube out...
  28. H

    Calculating pressure in a barometer

    A gas is contained in a vertical frictionless piston-cylinder device. The piston has a mass of 4 kg and cross sectional area of 35 cm2. A compressed spring above the piston exerts a force of 60N on the piston. If the atmospheric pressure is 95 kPa, determine the pressure inside the cylinder...
  29. U

    What is the Solution to the Mercury Barometer Problem?

    Homework Statement To construct a barometer, a tube of length 1m is filled completely with mercury and is inverted in a mercury cup. The barometer reading on a particular day is 76cm. Suppose a 1m tube is filled with mercury up to 76cm and then closed by a cork. It is inverted in a mercury cup...
  30. L

    Sum of energy in a system like barometer

    The drawing show a barometer with water inside. If I move up object with air inside I recover PV energy (P=external pressure, V=volume of object). If I want to move out object when it is at top, I need PV, is that ? So if it's that. If I replace: 1/ gravity by balls attracted with springs (for...
  31. B

    Torricelli Barometer and atmospheric pressure

    Homework Statement I have a Torricelli barometer column filled with mercury. Situation 1: Temperature1 = 20° C. Height: 0,760 m. Outer pressure:1 atm. Situation 2: Temperature2 = 35° C. Height: 0,762 m. Coefficient of termic dilation in the interval (T1, T2): 18,2 *10^-5 (°C)^-1 Find...
  32. M

    Barometer Planet: How a Barometer Works

    [PLAIN]http://www.barometerplanet.com/wp-content/uploads/2009/09/merc_barometer.jpg What makes mercury rise in the tube?Does atmospheric pressure carries the mercury in the tube?Is that true?
  33. T

    Calculating air density from a barometer?

    Homework Statement Working on a lab report, where we are asked to calculate the density of air. Ambient Temperature: 19°C Barometer (mm Hg abs): 765 There were two correction factors: 2.35 and 2.41 How do I use the above information to find the Air Density (kg/m3) ? What are the correction...
  34. K

    Will the Barometer level change?

    Homework Statement The mercury level in the barometer at sea level is recorded to be 76cm. So, I was wondering if you use a thinner tube. Will the mercury level change? At sea level, the pressure is 1 atm and thus according to the equation, p = hpg, whereby pressure is equal to the...
  35. G

    Question about a mercury barometer with an imperfect vacuum

    Homework Statement Homework question for a graduate level atmospheric science course: A mercury barometer of height h has an imperfect vacuum above its mercury column so that it measures a surface pressure of 29.80 inches Hg when the true surface pressure is 29.90 inches Hg, and it...
  36. B

    My Personal Hurricane Barometer Watch: Anyone Want To Join?

    Observed at Providence, Rhode Island: 05:30 UTC 28 August 2011: 29.68"Hg 05:45 UTC 28 August 2011: 29.67"Hg 06:00 UTC 28 August 2011: 29.68"Hg 06:15 UTC 28 August 2011: 29.70"Hg 06:30 UTC 28 August 2011: 29.71"Hg 06:45 UTC 28 August 2011: 29.70"Hg 07:00 UTC 28 August 2011: 29.67"Hg 07:15...
  37. T

    Barometer Problem: Reading When Freely Falling

    if a barometer is freely falling from a building , then what will be the reading shown on its tube?
  38. A

    Barometer reading in an elevator .

    Barometer reading in an elevator... Homework Statement A barometer kept in an elevator reads 76cm when it is at rest. If the elevator goes up with increasing speed , the reading will (a).increase (b)decrease (c)remain constant (d) become zero... Homework Equations The Attempt at...
  39. A

    Fluid mechanics barometer problem

    to construct a barometer,a tube of length 1m is filled completely with mercury and is inverted in a mercury cup.the barometer reading on a particular day is 76cm.suppose a 1m tube is filled with mercury upto 76cm and then closed by a cork.It is inverted in a mercury cup and the cork is...
  40. K

    Task of building a water barometer.

    Homework Statement Your physics teacher has assigned you the task of building a water barometer. You've learned that the pressure of the atmosphere can vary by much as 5 percent from 1 standard atmosphere as the weather changes. A. What is the minimum height you must build your barometer...
  41. T

    Calculating Altitude Using Barometer and Thermometer Readings

    I am no sure how to do this question? Do I have to use steam tables?
  42. L

    Fluid mechanics : Barometer - slight confusion

    What would happen to the mercury in the column if a barometer is accelerated upwards? In static condition, acceleration is g. When the system moves upward with an acceleration a, effective acceleration = g + a. The air above the mercury in the trough will press it with higher force...
  43. L

    Fluid mechanics : Barometer - slight confusion.

    What would happen to the mercury in the column if a barometer is accelerated upwards? In static condition, acceleration is g. When the system moves upward with an acceleration a, effective acceleration = g + a. The air above the mercury in the trough will press it with higher force...
  44. M

    Make a barometer that has a dial?

    Is this possible? If so, how do I do it?
  45. U

    How to Calculate the Scale of Venus's Atmosphere Using the Barometer Equation

    Venus's atmosphere is made up of CO2 which has a mean molecular weight of 44 atomic mass units. Given that the lower planetary temperature is 730K, use the barometer equation to determine the scale of Venus's atmosphere (the height at which pressure drops to 1/e of the surface pressure. Take...
  46. R

    Will there be changes to length of barometer if the following changes are made.

    Ok, ppl these r my doubts when is studies pressure, barometer. For each points i will need explanation. In fact, i really need them to help me understand, so i will really appreciate your effort. 1.will there be changes made to the length of mercury column when there is an addition of...
  47. T

    Barometer Tube Displacement: Solving for Isothermal Process

    Homework Statement A thin tube, sealed at both ends, is 1.00 m long. It initially lies horizontally, with the middle 10.0 cm containing mercury, and the two ends containing air at standard atmospheric pressure: See picture in attachment If the tube is now turned to a vertical position...
  48. G

    The size of the reservoir in a barometer

    im learning that the weight of a coloum of mercury in a barometer is balanced by the air pressure working on the reservoir at the base of the mercury tube..does the surface area over which the air pressure works matter? i understand that it is the height of the coloum,not the over all mass of...
  49. O

    Solved: Atmospheric Pressure Calculation Using Mercury Barometer

    [SOLVED] Pressure (Barometer) Homework Statement A mercury barometer of height 1.000m has some ideal gas trapped inside. When the tube is vertical, the height of the mercury column is 0.700m. When the tube is inclined at an angle of 30 degrees to the horizontal, the length of the mercury is...
  50. G

    Will the barometer reading rise or fall ?

    If i have a barometer which reads 76cm of hg when kept in an elevator when the elevator is at rest . now the elevator starts going up with some acceleration . will the barometer read less than , greater than or equal to 76cm of hg . also explain why . what will happen if the barometer is under...