Embed Size (px)
Citation preview
Does a balloon get heavier or lighter when you blow it up?
Hypothesis:
Task: design and conduct an experiment that tests your hypothesis. You may use any normal office supplies (balloons, rulers, tape, string etc.) and any lab equipment (rulers, balances, beakers) you might need.
Conclusion:
Brief Procedure:
Data:
4
Forza Science!!!!!
6
Pressure = Force / Area• Pressure is the amount of force
exerted over a given area.
• P = F/A– F is Force and the unit is Newtons
(N)– A is Area and the unit is Meters2
(m2)– The unit for Pressure is N/ m2 or
a Pascal (Pa)
– Force can also be measured in pounds (lbs)
– Area can also be measured in square inches
– Unis For Pressure can be psi (lbs/in2)
• If force is constant but area increases, pressure will
• If force is constant but area decreases, pressure will
• If area is constant but Force increases, pressure will
• If area is constant but Force decreases, pressure will
A 100lb person laying on one nail would result in a lot of pressure at that one spot. (100lb/nail)
A 100lb person laying on two nails would result in the pressure being spread out more. 100lb/2nails = 50lb/nail
A person laying on 20 nails displaces their weight over all of them reducing the pressure in each spot. 100lbs /20 nails = 5lbs/nail
[1][2][3][4]
[1][2][3][4]
Aluminum Ice Gold Wood
3kg2kg 4kg1kg
1kg1kg 1kg1kg
[1][2][3][4]
Rank these from highest pressure to lowest pressure
Pressure Formula Manipulation
Multiply both sides by a
Divide both sides by p
Under Pressure!
1. A Force of 15 Newtons is applied over a surface area of 0.6m2. What is the pressure?
2. A Force of 25 Newtons is applied over a surface area of 1.3m2. What is the pressure?
3. A pressure of 50 pascals is pushing down on an area of 5m2. What is the force?
4. A 20lb box with a length of 10 inches and a width of inches is resting on the floor. How much pressure does it exert on the floor?
11
Pressure, Volume and Temperature: Phet Physics
• What causes pressure in a balloon?
• Increasing the temperature of a gas at a fixed volume does what to pressure?
• Decreasing the temperature for a fixed volume of gas does what to pressure?
• Why should you never heat a closed container?
https://phet.colorado.edu/en/simulation/states-of-matter-basics
12
DANGER Axe Can Fire Baking Soda Rocket
• Exploding Beer Keg Kills Man
• NEW MILFORD, Conn. (AP) - October 24, 2006 -- Investigators were trying to determine who tossed a beer keg into a burning barrel at a party, causing a deadly explosion that sent metal shards slicing through a crowd of people.
• The explosion early Sunday killed Sean M. Caselli, 22, of New Milford. Seven other people were taken to hospitals with burns and shrapnel wounds, police said. Caselli was struck in the neck by a piece of flying metal.
• Sgt. Lee Grabner said investigators interviewed witnesses Sunday to try to identify the person witnesses say threw a quarter-keg of beer into the flames, and to determine whether criminal charges should be filed.
• Fires had been set in several barrels to keep people at the partygoers warm at the outdoors party in western Connecticut, said Police Captain Michael Mrazik.
• "This is a certain tragedy," said Police Chief Colin McCormack. "However, nothing I have been apprised of to this point in this investigation, which I caution is at the very early states, indicates a deliberate act on anyone's part."
• (Copyright ©2013 by The Associated Press. All Rights Reserved.)
13
Properties of Gas and Gas Laws
• Fills its container• Spreads easily• Mix well (e.g. air)• Low Density• Compressible• Mostly empty space
14
Gas in a Container
Boyle’s Law Gay-Lussac’s Law Charles’ Law
Constant Temperature Constant Volume Constant Pressure
15
Gas Law Summary
Boyle’s Law Gay-Lussac’s Law Charles’ Law
Constant Temperature Constant Volume Constant Pressure
As V↑P↓ As V↓P↑ As T↑P↑ As T↓P↓ As T↑V↑ As T↓V↓
16
Boyle’s Law
• For a fixed amount of gas at constant temperature:
• A Volume increases, pressure decreases.
• As volume decreases, pressure increases.
• P1V1 = P2V2 PHET PHYSICS APP
17
Gay-Lussac’s law
• For a fixed volume of gas :
• As temperature increases Pressure increases.
• As temperature decreases Pressure decreases.
• P1/T1 = P2/T2
PHET PHYSICS APP
18
Charle’s Law
• For a fixed amount of gas at constant pressure :
• As Temperature increases, volume also increases.
• As Temperature decreases, the volume also decreases.
• V1/T1 = V2/T2 PHET PHYSICS APP
Fluid Pressure! Why does your head hurt when you swim down deep in a pool?
POOL
The weight of the water pushing down on you creates pressure. The further down you go, the more water that is above you.
20
Your head hurts when you dive down in a pool because of the weight of the
water above you.
EARTH
What happens to air pressure as you climb a mountain?
As you go up there is less air above you
pushing down on you so air pressure decreases.
Why do mountain climbers use supplemental oxygen? What is
meant by thin air?
The density of air decreases as you go up. There is less and less of it because gravity pulls it close to the earth.
Air Pressure is measured with a Barometer
The weight of the air pushes down on the
liquid mercury.
The mercury is forced up the column.
Vacuum
The higher the air pressure the higher the mercury rises.
Current PressureSurface Map
Current Pressure
• In colder weather the air pressure on the earth’s surface is (higher| lower). Why?
• In warmer weather the air pressure on the earth’s surface is (higher| lower). Why?
Isopleths: contour lines (isobars)
Objective
Using a black colored pencil, lightly draw lines connecting identical values of sea level pressure. Remember, these lines, called isobars, do not cross each other. Isobars are usually drawn for every four millibars, using 1000 millibars as the starting point. Therefore, these lines will have values of 1000, 1004, 1008, 1012, 1016, 1020, 1024, etc., or 996, 992, 988, 984, 980, etc.
Procedure
Label each isobar with the appropriate value. Traditionally, only the last two digits are used for labels. For example, the label on the 1024 mb isobar would be 24. A 1008 mb isobar would be labeled 08. A 992 mb isobar will be labeled 92. These labels can be placed anywhere along the isobar but are typically placed around edges of the map at the end of each line. For closed isobars (lines that connect) a gap is placed in the isobar with the value inserted in the gap.
Analysis Isobars can be used to identify "Highs" and "Lows". The pressure in a high is greater than the surrounding air. The pressure in a low is lower than the surrounding air.
• Label the center of the high pressure area with a large blue "H".
• Label the center of the low pressure area with a large red "L".
High pressure regions are usually associated with dry weather because as the air sinks it warms and the moisture evaporates. Low pressure regions usually bring precipitation because when the air rises it cools and the water vapor condenses.
• Shade, in green, the state(s) would you expect to see rain or snow.
• Shade, in yellow, the state(s) would you expect to see clear skies..
In the northern hemisphere the wind blows clockwise around centers of high pressure. The wind blows counterclockwise around lows.
• Draw arrows around the "H" on your map to indicate the wind direction.• Draw arrows around the "L" on your map to indicate the wind direction.
Finished Product: NWS
Contour Maps of CT Mountains
CT Lakes and Ponds
Air always moves from high pressure to low pressure in an attempt to equalize.
Image via cmap
• When you go to the beach during the day, what is hotter, the sand or the water?
• When you go to the at night, what can you tell me about the water temperature?
Different materials heat up and cool down at different rates. Water
takes a long time to heat up and a long time to cool down.
Sea Breeze Cycle
• During the day the sand is really hot and the water is cool. • This leads to low pressure and rising air over the land and cold sinking air
over the water.• As the air on the sand rises air from the oceans moves in and fills it in.
Image via noaa
Land Breeze Cycle
• At night the sand cools really quickly but the water is comparatively warmer since it takes far longer to cool off.
• This leads to lower pressure and rising air over the water and cold sinking air over the land.
• As the air over the water rises air from the land moves in and fills it in.
Image via noaa
Demos to Explain
Demos to Explain• Paint Stick and Newspaper• Balloon and Flask• Egg and Bottle• Water stuck in a straw• Dart stuck on the board• Olive Oil Can• Can and Ice (Phet)
34
Pressure on a Balloon
Air Pressure from the atmosphere is pushing in.
Air Pressure from the compressed air inside the balloon is pushing out.
If you remove the atmospheric pressure the balloon expands. As a balloon rises it gets bigger.
Increasing atmospheric pressure will compress the balloon.
Lets put a balloon in a vacuum pump!
35
Pressure on a Balloon
Air Pressure from the atmosphere is pushing in.
Air Pressure from the compressed air inside the balloon is pushing out.
If you remove the atmospheric pressure the balloon expands. As a balloon rises it gets bigger.
Increasing atmospheric pressure will compress the balloon.
36
On the surface of the earth the pressure in your air
balances with the air pressure outside of it. As you ascend in a plane the
outside air pressure lowers but the pressure remains the same in your ears. It is pushing with a higher force and fortunately, it pops to
release the extra pressure…
Your ear is like a balloon Why Do Ears Pop?
37
What Happens to a Bubble blown underwater? Why?
http://www.youtube.com/watch?v=sn67vDBiL04
Why is it easier to Boil Water on a mountain?
38
When we heat liquid water it will evaporate and enter the air as a gas.
But there is air pressure pushing down on it which makes it harder for the water molecules to leave.
Air Pressure!If you remove or decrease air pressure boiling water will be much easier. Thus water boils quicker in Denver (think Mile High City!).
If you go up high enough to where the pressure is very low, your saliva will boil on tongue due only to the reduced pressure.
Is the glass half empty of half full?
100% Full!!!
50% Water
50% Air
Air Pressure
40
Air has mass so air has weight or air exerts a force on us.Since air exerts a force on us, there is air pressure.
Measure the surface area of your smartphone and calculate the weight of air pushing down on it assuming there is 14.7lbs of pressure per every square inch.
Do the same for a table in the room.
Why aren’t we crushed by this pressure?
41
We aren’t crushed because Pressure acts in all Directions
There is air in our bodies and it pushes out with the same pressure that the atmosphere is trying to crush us with
Pressure acts in all directions on an object
submerged in water.
Submarines actually compress (get smaller) as they dive deep. If they get too deep, SNAP, CRACKLE
AND POP!!!
Cross-Sectional View of a Submarine
In Casa A you have a string hung tightly from one side of a submarine to the other. If the submarine that was initially at the surface and descends 2000ft, what happens to the string?
In Casa B you have a string hung tightly from one side of a submarine to the other. If the submarine is initially at a depth of 2000ft and rises to the surface, what happens to the string.?
SAGSSNAPS
44
Air Pressure vs Water Pressure
Olive Oil
Water Pressure due to theweight of the water above.
Hole
Air Pressure
Air PressureAir Pressure
Air Pressure and Water Pressure balance when the top is on!
45
Air Pressure vs Water Pressure
Olive Oil
Water Pressure due to theweight of the water above and air pressure from above.
Hole
Air Pressure
Air PressureAir Pressure
Water comes out when the top is off! Since the container is no longer sealed not only is the weight of the water pushing down but the weight of air in our atmosphere is pushing down on it as well.
46
Is there Air Pressure in Outer Space?
Nasa.gov
Three Demos to Explain
• Coke Can in Ice Water• Heated Flask with Baloon• Egg in a Bottle
48
Pressure increases with Depth
• P = pgh• p = density (rho)– kg/m3 (water = 1000kg/m3)
• g = gravity (9.8m/s2)
• h = height (meters from surface)
• Where is the pressure the greatest? A,B or C.
POOL OF WATER
Pressure Increases
A
B
C
Surface
49
Hydrostatic Equilibrium: Derivation
• P = F/A [Force is weight of the fluid]• P = weight/A [weight = mg]• P = mg/A [D = m/V so m = DV]• P = DVg/A [V = LxWxH and A = LxW • P = Dg (LxWxH) / (LxW) [the LxW cancels]• P = Dgh [ we use p instead of D]• P = pgh
50
Hydrostatic-Problems• P = pgh• p = density (rho)
– kg/m3 – (water = 1000kg/m3)– (salt water = 1040kg/m3)
• g = gravity (9.8m/s2)• h = height (meters from surface)
1. In 1960 two men aboard the Trieste dove down to the deepest part of the ocean in the Marianas Trench in the Pacific Ocean. The reached a depth of over 10,911 meters. Calculate the pressure in pascals pushing down on the top of the submarine at that depth.
2. What is the pressure on a person’s head if she dives down 30 meters in a lake filled with fresh water?
3. What is the pressure on a submarine if it dives down 1000 meters in salt water.
4. At what depth in a pool of fresh water would a person experience a pressure of 29,400 pascals?
P1
P7P6 P5
P4
P2
P3
Imagine these are all very deep, very oddly shaped swimming pools. You have a pressure sensor and are going to determine the pressure at all seven locations. In which location(s) is pressure the smallest? In which is it the greatest? Rank them in order of smallest to highest pressure.
Lowest Pressure1234567Highest Pressure
Computer Lab Clicker Questions
52
53
Bernouilli’s Principle
• As the Speed of a moving fluid increases, the pressure of the moving fluid decreases.
• S P Siphoning Demo
54
A wing is shaped so that air traveling over the top of it has a longer path and moves faster. This means there is lower Pressure above a wing and higher pressure below it. This is called Lift!
Awesome Fluid Dynamics Demos That Are Not Bernoulli’s Principle
55
Pascal’s Principle and Hydraulics
56
What happens when you squeeze a tube of toothpaste?
Pascal’s Principle: A Change in pressure at any point in an enclosed fluid will be transmitted equally to all parts of the fluid.
57
What happens when you squeeze a tube of toothpaste?
Pascal’s Principle: A Change in pressure at any point in an enclosed fluid will be transmitted equally to all parts of the fluid.
P1 = P2
P1 P2
58
What happens when you squeeze a tube of toothpaste?
Pascal’s Principle: A Change in pressure at any point in an enclosed fluid will be transmitted equally to all parts of the fluid.
P1 = P2
F1 /A1 F2 /A2
F1 /A1 =F2 /A2
59
Hydraulic Device
A Small amount of Force can lift a very heavy object.
60
Hydraulic Device
F1 /A1 = F2 /A2
61
Pascal’s Principle Problem #1
• A Hydraulic lift uses Pascal’s principle to lift a 19,000N car. If the area of the small piston is (A1) equals 10.5cm2 and the area of the large piston (A2) equals 400cm2, what force needs to be exerted on the small piston to lift the car?
F1 / A1 = F2 /A2
62
Pascal’s Principle Problems
1. If a force of 100lbs is applied to the small piston (A1) which has an area of 12in2 and the area of the large piston (A2) is 300in2, how heavy of an object can be lifted?
2. A Hydraulic lift uses Pascal’s principle to lift a 4000lb car. If the area of the small piston is (A1) equals 4in2 and the area of the large piston (A2) equals 65in2, what force needs to be exerted on the small piston to lift the car?
F1 / A1 = F2 /A2
Hydraulic Brakes / Air Matresses
