5.1 Balloons

5.1 Balloons - Observations about Balloons • Balloons are...

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1 Key Concepts: 1. Pressure 2. Thermal Motion 3. Archimedes’ Principle 4. Ideal Gas Law HW#5 due Tuesday Observations about Balloons • Balloons are held taut by the gases inside • Some balloon float in air while others don’t • Hot-air balloons don’t have to be sealed • Helium balloons “leak” even when sealed States of Matter Solid -- definite shape and volume Liquid -- definite volume; shape of container Gas -- shape and volume of container Plasma -- highly ionized; gas-like Fluid -- take the shape of the container Question 1 How does air “inflate” a rubber balloon? – How does air occupy space? – How does it push on the balloon’s elastic skin? Air’s Characteristics • Air is a gas – Consists of individual atoms and molecules – Particles kept separate by their thermal energy – Particles bounce around in free fall Air & Pressure Air has pressure • Molecules bounce off walls of container and this exerts a force on the wall – Lots of small forces ( Mass small, but lots of molecules) • The larger the wall (surface area) the more force it experiences – Average force is proportional to surface area • Average force per unit area is called “pressure”
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2 Pressure Pressure = Force / Area Measured in: Newton per meter 2 or Pascal A Pascal is a small unit. Our air pressure is about 100,000 Pa That is 100,000 N on a square meter 100,000 N is about 22480 pounds 14.7 psi (pounds per sq inch) Air & Density Air has density – Air particles have mass – Each volume of air has a certain amount of mass – Average mass per unit volume is called “density” Air Pressure & Density Air pressure is proportional to: –Dens ity • Denser particles surface hit more often • Denser air more pressure Pressure Imbalances • Balanced pressure exerts no overall force – Forces on opposite sides of balloon cancel • Unbalanced pressure exerts an overall force – Forces on opposites sides of balloon don’t cancel – Forces push balloon toward lower pressure Increasing the volume, ________ A. Has no effect on the pressure. B. Increases the pressure. C. Decreases the pressure. Clicker Question 1 CQ2 CQ3 Cont. Increasing the number of molecules, ________ A. Has no effect on the pressure. B. Increases the pressure. C. Decreases the pressure. Clicker Question 2 CQ4 Cont.
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3 Increasing the temperature, ________ A. Has no effect on the pressure B. Increases the pressure C. Decreases the pressure Clicker Question 3 Question 2 Why doesn’t the atmosphere collapse?
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This note was uploaded on 02/07/2010 for the course PHY 1405 taught by Professor Russell during the Fall '07 term at Baylor.

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5.1 Balloons - Observations about Balloons • Balloons are...

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