Atmosphere What have we discovered about air so far? – Is matter - has mass & occupies space – Is mixture of gases - mostly nitrogen & oxygen – Made of individual nitrogen & oxygen molecules flying through space – Can heat up & cool down – Gets denser as it cools, less dense as it warms
Atmosphere Planet Earth is completely surrounded by a thin layer of air. – Called the atmosphere – Extends up about 300 miles above Earth’s surface – Most of the air is in first 9 miles
Investigating Air Use syringe and plastic tube to find out more about air. Answer the following questions: – What happens to air in the syringe when you push and pull on the plunger? – What can air do?
Air & Syringes Record your observations on notebook sheet Try investigations on sheet - record observations and any questions What observations did you make? What questions do you have?
Air Observations When you clamp the tube closed and push the plunger down, what happens to the air? Is there more air, less air, or the same amount of air in the syringe when the air is pushed into a smaller space? – How do you know? What happens when you let go of the plunger after pushing it down?* What do you think happens to the air when it is pushed into a smaller space? What happens to push the plunger back out when you release the plunger?
Compression and Pressure When you push on the plunger, the air is forced into a smaller space. – The air is compressed – Same amount of air is still in the syringe when compressed Compressed air pushes back with a force equal to the force compressing it. – Pushing force is called pressure – If force on plunger is released, the pressure in the compressed air will push the plunger out
Molecular Model of Air Air is made of tiny particles – Called molecules – Made mostly of Nitrogen & Oxygen molecules – So tiny you can’t see them – Free to move around - not attached – Lots of space between molecules in gases
Bottle Demonstration What do you think will happen to the bottle when I suck on the tube? Why did the bottle get crumpled? What caused the bottle to collapse?* Bottle collapsed and crumpled for the same reason a syringe plunger moves in and out “by itself” when connected to a second syringe. What causes plunger in syringe #2 to slide in and out when you push and pull the plunger in the syringe #1?
Atmospheric Pressure Syringe has a little bit of air trapped between rubber tip of plunger and clamp. – Air molecules are flying around & banging into each other, sides of syringe, & plunger tip – Air molecules outside the syringe also flying around; banging into each other, outside of syringe, & back side of syringe plunger. – Banging produces pressure – Air inside syringe pushes on inside of syringe; air outside syringe pushes on outside of syringe
Atmospheric Pressure Applying force to plunger to pull it out. – Release plunger, it slides back into barrel by itself – What makes the plunger go back into the barrel where it started? Atmospheric Pressure! – Pull plunger = larger space but same number of molecules – Pressure is less inside syringe – Pressure is greater outside syringe – Plunger is pushed back until pressure is equal both inside and outside
Atmospheric Pressure Atmospheric pressure is pressure due to the mass of air pulled to Earth by gravity. – Same in all directions - upward, downward, & to the sides – Air is pushing on every side of you & everything else on Earth’s surface with equal force CompleteAtmospheric Pressure at Work sheet
Vocabulary Compress – squeeze (air) molecules into a smaller volume (space) Pressure – force or push caused by moving molecules Atmosphere – layer of air around Earth Atmospheric pressure – Force applied in all directions by the air in Earth’s atmosphere
Content Whathappens when air is pushed into a smaller space? – Air molecules move closer together, resulting in compressed air What causes atmospheric pressure? – The weight of air Homework: Read The Pressure is On! and answer questions
The Pressure is On! What is atmospheric pressure and what causes it? Is atmospheric pressure higher on a mountaintop or at sea level? Why did the bag of chips puff up over Tioga Pass? Why was the empty water bottle crushed when they returned to San Francisco?
Summary: Heating Earth What causes uneven heating of Earth’s surface? How does uneven heating of Earth’s surface results in convection currents? What is atmospheric pressure and what causes it? In what direction does atmospheric pressure push?