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STATION 1 Balloon in a Vacuum ***CAUTION***: at this station, all students must wear eye protection the entire time the vacuum pump is in operation. Please be careful and use the equipment as directed. Failure to follow directions could lead to serious injury or death. Thank you for following directions. PURPOSE: To show the affect the atmosphere has on objects on this planet. Questions: 1. What did the balloon do when you turned on the vacuum pump? Why? a. Expand because the air pressure decreased inside the glass container and allowed the air in the balloon to increase in volume. 2. Why don’t we feel or really notice the atmosphere? a. Because it pushes equally on us from all sides. It is also because we are mainly water and water does not compress when pressure increases. 3. What does the balloon look like when the air pressure goes back to normal? Where in the real world could a vacuum be used for consumer goods or in the real world? a. It looks like normal before you stated the vacuum pump. b. Vacuum-packed foods (the stuff the astronauts eat or the pop you here when you open up a bottle of Snapple’s. The safety feature to let you know that no one opened the bottle before you purchased it). 4. Explain what happens to a bag of potato chips when you go up in an airplane? What would the bag look like after you landed if, during the flight, you opened the bag then sealed it while at 30,000 feet? Why? a. When the bag goes up in elevation there is less atmospheric pressure (because there is less air as we go up). This allows the air inside the bag to expand and increase the volume of the bag (so it gets big and puffy). b. If you opened (and closed again) it at 30,000 feet where the atmospheric pressure is less than sea level, the bag would be compressed when the plane lands because the atmospheric pressure is greater at sea level. The chips would still be a tasty treat that could still be enjoyed as the cornerstone of any nutritional meal (what movie is that inspired from?). STATION 2 Three Holes and a Bottle PURPOSE: To show what causes air pressure & that it does not discriminate. Questions: 1. Which hole has a stream that goes the furthest? Explain what is causing what you are seeing to happen? a. The bottom stream goes the furthest because it has the greatest amount of pressure on it. It happens because it has the most water plus the atmosphere applied to it. The atmosphere, plus the water above each hole is what is applying the pressure for the water to squirt out the holes. 2. What is forcing the water to move out of the holes? What force is keeping all the level of the red liquid the same in four glass tubes? a. Air pressure and the weight of the water above it. b. Air pressure (atmospheric pressure). 3. What force is causing the atmosphere to push down on us? a. Gravity is what is causing there to be air pressure. If there was no gravity, there would not be a force forcing down the air. 4. If you were on Mars where the atmosphere is 1/100th as thick as our atmosphere, would the water shoot out further than on Earth? a. No, the water would not shoot as far for two reasons. First, the gravity on mars is less than on Earth (2/3rd). This means there is less force pulling the atmosphere towards the ground (so less air pressure). Second, the atmosphere is 1/100th as thick so there is less mass pushing down on the planet. The decrease in pressure results in a decrease atmospheric pressure. 5. Why do we feel a lot of pressure on our ears when we swim to the bottom of a pool (12 feet or 4 meters deep), but do not feel the same pressure when we go down a flight of stairs (12 feet or 4 meters down)? a. This is due to the pressure applied by the water on your Eustachian tubes (the ones that pop when you go up in an airplane or the mountains). Since water has a density of 1 g/cm3 and air has a density of .0012g/cm3 (or almost 1000 times less dense), there is more mass (and pressure (force)) pushing on your body. b. FYI – the atmosphere has a pressure of 14.7 lb/in2. 32 feet of ocean water is equal to one atmosphere. The atmosphere is approximately 20 miles high. It is the density of water compared to the density of air that makes the difference in the pressure our body feels when we go swim with Flipper in the beautiful ocean. STATION 3 Under Pressure *Pascal’s Principle- when force is applied to a fluid in a closed container the pressure is transmitted equally to all parts of the fluid (gas / liquid). Questions: 1. Which syringe is easier to push down? Explain it in terms of Pascal’s principle. The syringe with less surface area (the small syringe) is easier to push down. If you look at the formula for pressure (P=Force/Area) you will see that force that is needed to push down each syringe is different because the area (surface area) for each syringe is different. Now, Pascal’s Principle states that the pressure in a closed container is equally everywhere in the closed container. This means the pressure on the water is the same in the big syringe as in the little syringe when you push down on either one. If P (pressure) is equally on the liquid from each syringe that means the force to move them will be different because the area each one covers is different. The bigger syringe has a larger area so it will need to have a bigger force applied to it compared to the small one. 2. Other than one syringe being harder to push then the other, what other difference do you notice when you push down the larger vs. smaller syringe? The smaller one is easier to push down, BUT does not cause the big syringe to move up as far as when the big syringe is pushed. The big syringe is moving a larger volume of air so it causes the little syringe to move upwards more when the big syringe is pushed. 3. Where is the pressure the greatest when you are pushing down on the small syringe? Where is it the greatest when pushing on the large syringe? The pressure is equal everywhere when pushing either of the syringes. This is what Pascal’s Principle states. 4. Which syringe contains water with the greater density? Why? The densities of the water are the same for each one for two reasons. First, density of matter is unique to the matter. All water at STP (standard temperature and pressure) has a density of 1 g/cm3. It does not matter where the water is in the syringe it still is water. Second, the water in the syringes is in a closed system with a force being applied. According to Pascal the pressure on the water is equal everywhere in the closed container. This means that the density (which does increase slightly because of the increased pressure) is the same for all the water in the syringes. 5. Which syringe can hold the greatest volume of water? The larger syringe can hold the greatest volume of water and also the greatest mass of water compared to the smaller syringe. The large syringe can hold 60 ml (60 cc) of water and the smaller one can only hold 10 ml (10 cc). 6. Give three examples in the real world where you would see a hydraulic (liquid filled) or pneumatic (gas filled) device that uses Pascal’s principle? Three or more examples from the real world would be: bike pump, elevator, hydraulic lift or press, shocks on a car, pogo stick, squirt gun, water pipes at your home, thermometer, scuba tank, air compressor, air powered tools, air bag in your car, and so many, many more… STATION 4 Tornado in a Bottle PURPOSE: To demonstrate how cyclones (low pressure systems) move and how the physics we have studied are involved. Questions: 1. Why do you need to swirl the bottle around? Will it work if you do not swirl it around? a. To get the potential energy to transfer to kinetic energy. If you do not swirl the water around, the air pressure in the bottom bottle pushes on the water above and does not allow it to go down. (It is like when you put your finger on a straw filled with soda and the liquid does not fall from the straw until you remove you finger). b. Not really. You need to create low pressure in the middle so it will start to flow. It has a low pressure middle because moving air has a lower pressure than still air. Remember, warm air rises and cold air sinks. In the eye of the storm, there is cold, dry air descending. 2. Which way do storms (low pressure systems) rotate in the Northern hemisphere? Which way do high pressure (anticyclone) systems rotate? What happens in the Southern hemisphere? a. In the Northern hemisphere, low pressure (cyclones) rotate counterclockwise. High pressure (anticyclones) rotate clockwise. In the Southern hemisphere, low pressure systems rotate clockwise and high pressure rotate counterclockwise. 3. What principle of physics explains why the middle should have no water in it (think roller coaster project)? What is the middle a hurricane called? a. The force that goes towards the outside of a circle, the centrifugal force (also Newton’s First Law of Motion – things in motion tend to stay in motion). Water swirls the fastest at the outer part of the tornado and slower in the middle (just like the propeller of a plane or a merry-go-round. It is the most fun to be on the outside of this type of ride because it spins faster compared to the middle). b. The eye. Cold, dry air descends in the middle of the eye. It is low pressure and generally the calm part of the storm. People enter the eye and get a false impression that the hurricane is over. There is still the other side of the hurricane to come. 4. When and where (in the United States) do tornados usually form? What types of fronts or conditions are involved? a. During the spring, time in the Midwest. b. When warm, moist air from the Gulf of Mexico meets with cold, dry air mass from the North. Cold fronts from Canada meeting warm fronts from the Gulf of Mexico. 5. How are hurricanes and tornados similar? How do they differ? a. Both have violent winds and can cause serve damage and destruction. Both have a low pressure middle (the eye) where the winds are calm (the eye in the tornado is very small so there really isn’t a calm in a tornado). Cold dense air descends (goes down) and warmer moist air ascends (goes up). Hurricanes occur over warm ocean waters and tornados form over land where warm & cold fronts meet. STATION 5 Moving Air while Moving Bodies PURPOSE: To show the relationship between pressure and volume. To show that moving air is less dense than stagnant (still air) and that cool, unexpected things happen because of this (Bernoulli’s Principle). IMPORTANT: moving air is less dense than still air. Questions: Part I: “Rolling Coke Cans “ 1. Which way does the coke cans roll? a. To the middle. This is where the volume of air has increased (more space between air molecules, less dense (density = mass/volume), but the pressure is less so the cans want to go where there is less pressure or push on them. This is why motorcycles are pulled towards on coming big rigs on two lane highways. Bernoulli’s Principle states that the faster the air moves, the less pressure it exerts. 2. Where is the air the densest? The least dense? a. On the sides of the cans. In the middle where the air is moving. 3. When you blow through the cans, are you increasing or decreasing the pressure? What about the density of the moving air? a. Decreasing the pressure when you blow. The density is decreasing, but the volume is increasing (air molecules are further apart, moving faster). Bernoulli’s Principle (see vocab) Part II: “Dancing Ping Pong Balls“ 1. What happens to the ping pong balls when you blow between them? a. They move closer together because of the low pressure you are creating. 2. What happens if you blow on the outside? a. The one you blow next to moves a little to the side. The tape on the ping pong balls seems to have made it difficult for you to see that. 3. Explain what is happening? a. There is lower pressure (less of a push by the air) so the balls move to the lower pressure area (the middle) because the denser air is pushing it towards the less dense air. The density has decreased so now there is more room for air and the ping pong balls to slide into. STATION 6 Pressure & the Cartesian Divers PURPOSE: To show how gases and liquids react to increased pressure and how the changing of air’s density causes the Cartesian diver to move. Part I: Squidy, Hook, Spinner, & Friends Questions: 1. Why does Squidy, Hook, or Spinner go to the bottom of the bottle when you squeeze it (talk about the density of the air, not the water)? a. The pressure is increasing on the air, so the density of the air inside the dropper increases. When the dropper is first put into the bottle it just barley floats because its density is just a tiny bit less than the water. When you squeeze the bottle, you are increasing the density of the water and the air inside the little diver person. Right now you are probably saying, “Well, Mr. Mathot, if the density of the water is now greater, shouldn’t the diver person float better? That is a very good question, very good, even logical. BUT: The air in the diver person is also increasing in density. In fact, the density of the air is changing more than that of the water. Here is the KEY: Air is easier to compress and make denser compared to water (water doesn’t compress very well). When you squeeze the bottle, the air in the diver person is compressed (decreases in volume) so much that it changes the density (density=Mass/Volume) enough for the diver person to now be denser than the water and sink to the bottom. Part II: Air in a Syringe Questions: 1. What does the syringe filled with air remind you of in the real world? How could it be used or where is it used in the real world? a. It might remind you of a air pump, needle at the doctor’s office, a piston on a machine, shocks on a bike, or anything else that is a closed container filled with a fluid (gas or liquid). 2. Which syringe is easiest to compress (water filled or gas filled)? Explain why using density and your knowledge of liquids and gases. a. The gas (air filled) syringes. This is because air is less dense than water. Air still has space for the molecules to be pushed together. Water is too dense for it to be compressed further (for the most part). Let me give you an example: Someone in 1st or 2nd period was so strong (or they did not follow Mr. Mathot’s warning) they cracked the plastic of the water filled syringe. The water did not want to be compressed anymore so the force was transferred into the plastic and cracked it. 3. Could you ever compress the syringe completely if it was full of air? Explain your answer. a. No, because the air takes up space and needs space to exist in (you can not destroy matter). The pressure would increase so much that either the container would explode or there could not be any more pressure applied to the air in the container. Gas Laws – VTP Lab V Volume T Temperature P Pressure Conclusion/Questions: Part A 1. Put your pencil through the middle hole (that is holding the temperature constant); push down on the part of the card labeled volume. That shows the effect of lowering the volume. What happens to the volume when the pressure is increased? a. The volume decreases. 2. What happens to the volume when the pressure is decreased? a. The volume increases. 3. What GAS LAW states this? a. This is Boyle’s Law. Part B 4. Place a pencil through the pressure hole indicating holding pressure constant. What happens to the volume if you decrease the temperature? a. The volume decreases. 5. What happens to the volume if you raise the temperature? a. The volume increases. 6. What GAS LAW states this? a. This is Charles’s Law. Part C 7. Place a pencil through the volume hole. This indicates holding volume constant. What happens to the pressure if you raise the temperature? a. The pressure increases. 8. What happens to the pressure if you lower the temperature? a. The pressure decreases. 9. Why do you think gases can be compressed, but liquids and solids cannot? a. Gases can be compressed because they are less dense than liquids and solids. Liquids and solids cannot be compressed much if at all because their atoms are already very closely packed together (dense). 10.Why is it extremely dangerous to put dry ice in a closed container? Use your VTP card to explain this puzzle. a. The volume remains the same (until it explodes) while the temperature increases (CO2 sublimes) and the causes the pressure to increase greatly. BONUS: If you increase the pressure then you increase the density because the molecules are “squeezed” closer together (denser). CARTESIAN DIVER Lab (A LOOK AT Pascal’s Principle) Answers 1. See the three purposes from the lab sheet. 2. The dropper goes down to the bottom when you squeeze the bottle and it goes back up to the top when you release. If you look at the diver when you squeeze the bottle you will notice that the air gets compressed and the volume of the air decreases. This causes the diver to increase in density and sink. The opposite happens when you release the hounds from the bottle. 3. The pressure of the water increases and so does the pressure on the air. The density of the air, however, changes more than that of the water. This causes the diver to become denser than the water, even though, the diver has air in it. 4. Some of the water is pushed into the dropper because air can be compressed more than water because air is less dense and liquids in general do not compress much when there is a force applied. 5. The diver sinks because the force (of pushing on the bottle) causes the water to have more pressure on it and that results in the air having more pressure on it. The density of the water stays almost the same, but the density of the air increases so that now the Cartesian diver dude is denser than the water. This is why he/she goes to the bottom (it’s all about density). 6. If the density of an object is less than the fluid, it will FLOAT. If the density is greater than the fluid, it will SINK. Water has a density of 1 g/cm3 (fresh). This means if the density of a piece of wood is .8 g/cm3 the wood will float. 7. When pressure drops the density of air decreases (becomes less dense and more spread out (larger volume)). 8. When pressure increases the density of air increases (becomes denser and less spread out (smaller volume)). 9. It is equal in pressure everywhere in the fluid. Pressure, like gravity, does not discriminate. 10. Gases are less dense than liquids and solids and still have room for their atoms to get denser.