Why does the earth “have more gravity,” i.e. g is larger on earth, than does the moon?
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Physics 1710Physics 1710—Warm-up Quiz—Warm-up QuizWhy does the earth “have more gravity,” Why does the earth “have more gravity,” i.e. g is larger on earth, than does the i.e. g is larger on earth, than does the moon?moon?
A B C D E
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A.A. The earth as an atmosphere.The earth as an atmosphere.B.B. The earth has a larger diameter.The earth has a larger diameter.C.C. The earth has more mass.The earth has more mass.D.D. The earth rotates faster.The earth rotates faster.E.E. None of the above.None of the above.
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Analysis:Analysis:
• The earth has an atmosphere because of The earth has an atmosphere because of its larger g, not vis versa.its larger g, not vis versa.
• The larger diameter means smaller The larger diameter means smaller g~1/Rg~1/R22
• The larger mass of the earth m = 4/3The larger mass of the earth m = 4/3πρRπρR33 makes a larger g=GM/makes a larger g=GM/RR22
•Gravity has nothing to do with the rate of Gravity has nothing to do with the rate of rotation.rotation.
Physics 1710Physics 1710—C—Chapter 14 Fluid hapter 14 Fluid DynamicsDynamics
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Summary: Summary: •Pressure Pressure is the force per unit area. P =F/A is the force per unit area. P =F/A
• Unit of pressue [Pacal] = [N]/[mUnit of pressue [Pacal] = [N]/[m22]]
•The The hydrostatic pressurehydrostatic pressure is P = P is P = Poo + + ρρghgh
• Archimedes’ PrincipleArchimedes’ Principle: F: Fbouyant bouyant = = ρρfluid fluid g Vg V
• Equation of ContinuityEquation of Continuity: A: A11vv11 = A = A22vv22
• Bernoulli’s Equation:Bernoulli’s Equation: P + ½ ρvP + ½ ρv22 + ρgy = + ρgy = constant.constant.
Physics 1710Physics 1710—C—Chapter 14 Fluid hapter 14 Fluid DynamicsDynamics
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80/20Pressure = Force per unit Area
P = F /A
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80/2080/20The unit of pressure in SI units is The unit of pressure in SI units is the the
Pascal [Pa] = 1 Newton/ mPascal [Pa] = 1 Newton/ m22
1 Newton 1 Newton forceforce
1 square meter 1 square meter areaarea
1 Pascal 1 Pascal pressure:pressure:
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80/2080/20Standard atmosphere = 1.0 Standard atmosphere = 1.0 atm atm
=101 kPa=101 kPa
=14.7 psi=14.7 psi
Tire Tire pressurepressure
A few 100 A few 100 kPakPa
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Which applies Which applies
the greatest the greatest
pressure on pressure on
their foot?their foot?
Physics 1710Physics 1710—C—Chapter 14 Fluid hapter 14 Fluid DynamicsDynamics
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Which applies the greatest Which applies the greatest pressure on their foot?pressure on their foot?
A B C
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A.A. Man. Man.
B.B. Elephant. Elephant.
C.C. Woman.Woman.
Physics 1710Physics 1710—C—Chapter 14 Fluid hapter 14 Fluid DynamicsDynamics
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Force = 200 lb = Force = 200 lb = 891 N891 N
Force = 4,000 lb = Force = 4,000 lb = 17,800 17,800 NN
Force = 100 lb = Force = 100 lb = 445 N445 N
Foot Area = 36.2 inFoot Area = 36.2 in22 = = 0.023 m0.023 m22
Foot Area = 43.5 inFoot Area = 43.5 in22 = = 0.028 m0.028 m22
Foot Area = 12.7 inFoot Area = 12.7 in22 = = .0082 m.0082 m22
p = F/A =200/(2 x 36.2) = 2.8 psip = F/A =200/(2 x 36.2) = 2.8 psip = 891/(2 x 0.023) = p = 891/(2 x 0.023) = 19 kPa19 kPa
p = F/A =4000/(4 x 43.5) = 23. psip = F/A =4000/(4 x 43.5) = 23. psip = 17800/(4 x 0.028) = p = 17800/(4 x 0.028) = 159 kPa159 kPa
p = F/A =100/(2 x 12.7) = 3.9 psip = F/A =100/(2 x 12.7) = 3.9 psip = 445/(2 x 0.0082) = p = 445/(2 x 0.0082) = 27 kPa27 kPa
Physics 1710Physics 1710—C—Chapter 14 Fluid hapter 14 Fluid DynamicsDynamics
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Force = 100 lb = Force = 100 lb = 445 N445 NHeel Area = 0.16 inHeel Area = 0.16 in22 = = .0001 m.0001 m22p = F/A =100/(2 x 0.16) = 313. psip = F/A =100/(2 x 0.16) = 313. psip = 445/(2 x 0.0001) = p = 445/(2 x 0.0001) = 2200. kPa2200. kPa
p = p = 19 kPa19 kPa
p = p = 159 kPa159 kPa
p = p = 27 kPa27 kPa
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The Mysterious Swami Seat
Physics 1710Physics 1710—C—Chapter 14 Fluid hapter 14 Fluid DynamicsDynamics
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80/20Pressure = Force per unit Area
p = F /A
Same ForceSame Force
Different AreaDifferent Area
∴∴Different Different PressurePressure
Physics 1710Physics 1710—C—Chapter 14 Fluid hapter 14 Fluid DynamicsDynamics
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Pressure is the hydraulic stress:Pressure is the hydraulic stress:
Hydraulic Stress: Hydraulic Stress: Bulk Modulus BBulk Modulus B
Stress = modulus x strainStress = modulus x strainσ = σ = F/A = p = B F/A = p = B ε = B ε = B ΔV/VΔV/V
Physics 1710Physics 1710—C—Chapter 14 Fluid hapter 14 Fluid DynamicsDynamics
PPVV
ΔVΔV
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Pressure is isotropic:Pressure is isotropic:
Physics 1710Physics 1710—C—Chapter 14 Fluid hapter 14 Fluid DynamicsDynamics
PP
VV
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Pressure is isotropic:Pressure is isotropic:
Physics 1710Physics 1710—C—Chapter 14 Fluid hapter 14 Fluid DynamicsDynamics
PP PPPP PP
F1= A1P; F2 = A2P
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Hydrostatic Pressure is due to weight Hydrostatic Pressure is due to weight of fluid above:of fluid above:
Physics 1710Physics 1710—C—Chapter 14 Fluid hapter 14 Fluid DynamicsDynamics
F = m g = (Ah)ρfluid g
P = F/A = ρfluid g h
hAA
PP
FF
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Archimedes PressureArchimedes Pressure
Physics 1710Physics 1710—C—Chapter 14 Fluid hapter 14 Fluid DynamicsDynamics
F = AΔP - mg= A ρfluid g Δh – mg
F = Fbouyant - mg
Fbouyant = ρfluid g V
PP
AA
- mg
VPP
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Archimedes PressureArchimedes Pressure
Physics 1710Physics 1710—C—Chapter 14 Fluid hapter 14 Fluid DynamicsDynamics
Fbouyant = ρfluid g V
PP- ρfluid V g
VVPP
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ContinuityContinuity
Physics 1710Physics 1710—C—Chapter 14 Fluid hapter 14 Fluid DynamicsDynamics
V constant if fluid is incompressible.
A1v1 = A2v2
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Work done on fluid Work done on fluid
Physics 1710Physics 1710—C—Chapter 14 Fluid hapter 14 Fluid DynamicsDynamics
ΔW = ½ m v2 + mg y
dW/dV = ½ ρ v2 +ρg y = d (Fy)/dV = dF/dA =ΔP
½ ρ v2 +ρg y =ΔP
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Summary: Summary: •Pressure Pressure is the force per unit area. P =F/A is the force per unit area. P =F/A
• Unit of pressue [Pacal] = [N]/[mUnit of pressue [Pacal] = [N]/[m22]]
•The The hydrostatic pressurehydrostatic pressure is P = P is P = Poo + gh + gh
• Archimedes’ PrincipleArchimedes’ Principle: F: Fbouyant bouyant = = ρρfluid fluid g Vg V
• Equation of ContinuityEquation of Continuity: A: A11vv11 = A = A22vv22
• Bernoulli’s Equation:Bernoulli’s Equation: P + ½ ρvP + ½ ρv22 + ρgy = + ρgy = constant.constant.
Physics 1710Physics 1710—C—Chapter 14 Fluid hapter 14 Fluid DynamicsDynamics
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No Talking!No Talking!Think!Think!
Confer!Confer!
Peer Instruction Peer Instruction TimeTime
Why does the platform spin faster Why does the platform spin faster when he brings his arms in?when he brings his arms in?
Physics 1710Physics 1710—C—Chapter 11 App: E & Ehapter 11 App: E & E
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Why does the platform spin faster when he Why does the platform spin faster when he brings his arms in?brings his arms in?
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A B C D E
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A.A. He increases his angular He increases his angular momentum.momentum.
B.B. He increase his moment of He increase his moment of inertia.inertia.
C.C. He decrease his moment of He decrease his moment of inertia.inertia.
D.D. He pushes against the He pushes against the inertia of the weights.inertia of the weights.
E.E. None of the aboveNone of the above
Answer Answer Now !Now !
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Physics 1710Physics 1710—C—Chapter 11 App: E & Ehapter 11 App: E & E
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Where should the fulcrum be place to balance the teeter-totter?
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B.B.
C.C.
Answer Answer Now !Now !
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Physics 1710Physics 1710—C—Chapter 14 Fluid hapter 14 Fluid DynamicsDynamics
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Which way will the torque ladder move?1010
A B C
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A.A. Clockwise Clockwise B.B. CounterclockwiseCounterclockwiseC.C. Will stay balancedWill stay balanced
Answer Answer Now !Now !
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Physics 1710Physics 1710—C—Chapter 14 Fluid hapter 14 Fluid DynamicsDynamics