Download Barometer in a Bottle - UF Chemistry Club

University of Florida Chemistry Outreach Program
Barometer in a Bottle
Estimated Time: 30 mins. + 15 mins. clean-up, observation could be
expanded to occur over several days (supervised by teacher)
Topics: Atmospheric pressure
Introduction: Atmospheric pressure refers to the weight of air above any given point. Areas with low
atmospheric pressure have less air above them, and measurements that read low atmospheric pressure (example:
toward the top of mountainous regions) indicate that the total “mass” of the air above it is lesser than what
would be observed if measurements were taken in a higher atmospheric pressure area (such as in valleys or at
sea level). A metaphor for explaining atmospheric pressure is to imagine the latter to be like layers of blankets;
the higher up you are in the atmosphere, the fewer blankets you have. More blankets are heavier, and as a result
translate into higher atmospheric pressures. The study of atmospheric pressure is important because it can allow
for easy prediction of weather patterns. Air moves from areas of high pressure to low pressure, causing winds.
Variations in atmospheric pressure at constant height can allow forecasters to predict rain. High pressure
systems indicate that moisture in the air will remain as-is, without precipitation. In contrast, low pressure
systems suggest that water vapor will condense, form water droplets, and eventually result in downpour.
Atmospheric pressure is measured using a device called a barometer. Most barometers are mercury or water
based. The one created in this lab is much simpler (less accurate), but still effective in observing basic
atmospheric pressure changes.
Objective: To understand the concept of atmospheric pressure by its effect on the weather and by measuring it
with a homemade barometer. Emphasize that high pressure in a region indicates fair weather while low pressure
suggests that rain/snow is imminent.
Materials: - Small balloons
-Index cards
- Straw
-Scissors
-Tape
Safety:
-Paper and pencil for recording
-250mL beaker
-Supervise younger children with scissors.
Procedure:
1. Cut the neck-end of the balloon off and discard.
2. Stretch the balloon over the rim of the beaker, including the lip of the beaker. Make sure the balloon fits
nearly flat over the mouth of the beaker like a sheet of paper.
3. Tape a straw such that one end of the straw is attached to the center of the balloon, while the other end
protrudes off the edge of the beaker.
4. Tape a piece of index card to the beaker (perpendicular to the straw) and trim the straw so that it makes
a pointer on the card. Mark where the pointer starts.
5. Students will be able to watch the straw move up and down as the balloon expands and contracts with
atmospheric air pressure. The pointer/straw will indicate changes along the marked index card.
Discussion:
1. What does it mean when atmospheric pressure is high?
It usually means water in the air will remain a vapor and we will have a sunny or nice day.
2. What does it mean when pressure is low?
Water in the air turns to tiny liquid droplets and we have a cloudy or rainy day.
3. When does low pressure turn to rain?
When the tiny liquid droplets stick together.
The balloon will expand and contract based on the air pressure around it. When atmospheric pressure goes
down, the air in the jar expands and causes the balloon to swell and the pointer (straw) to go down. When
atmospheric pressure increases, the weight of the air pushes down on the balloon such that the pointer goes up.
Students can watch their barometers on stormy days and observe (in all likelihood) lower air pressure in the
atmosphere around them. Forecasters use advanced barometers combined with satellite imagery to predict the
weather in this manner.
Source:
This lab is a modified version of a similar activity from NyeLabs.com