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Day 59 Physics UCM. LO: SWBAT perform calculate Fc and Ac LO: SWBAT Calculate Fg using NULG AGENDA Do Now – Complete UCM worksheet Notes Worksheet HW22 due Thursday. Newton’s Law of Universal Gravitation. Sir Isaac Newton (1642-1727). 60R earth. R earth. Constant of proportionality.
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Day 59 Physics UCM LO: SWBAT perform calculate Fc and Ac LO: SWBAT Calculate Fg using NULG AGENDA Do Now – Complete UCM worksheet Notes Worksheet HW22 due Thursday
Sir Isaac Newton (1642-1727)
60Rearth Rearth
Constant of proportionality M1 M2 r Newton’s Law of Gravity
Cavendish, Henry (1731-1810) • Measured G in 1798 G = 6.67 x 10-11 Nm2/kg2
(3)(4) F = (6.67 x 10-11) 22 2 m 4 kg What is the force between Kiwi and a book? F = 2 x 10-10 N 3 Kg
(3)(4) F = (6.67 x 10-11) 22 F cat, book F book, cat 4 kg What is the force between Kiwi and a book? 1,2 F = 2 x 10-10 N or?? 3 Kg
(5.98 x 1024 kg) Mbook Wearth,book = (6.67 x 10-11Nm2) (6.38 x 106 m)2 kg2 r= 6.38 x 106 m What is the force between the Earth and a book? Wearth,book = Mbook(9.8 N/kg) Mearth = 5.98 x 1024 kg
But you ask why is “g” independent of mass? • F = m1g = Gm1mearth/r2 • Note that the m1’s cancel on both sides and: • g = Gmearth/r2
What’s his weight? 648 N !
Apollo 17 Earth as seen from the Moon
At the surface of the Earth: Wearth,Story = MStory(9.8 N/kg) = (80 kg) (9.8 N/kg) = 784 N rearth = 4000 miles
400 miles above the surface : Wearth,Story = MStory(8.1 N/kg) = (80 kg) (8.1 N/kg) = 648 N rearth = 4000 miles
NFS NSP person scale WES WEP NPS Which force does the scale read? Apparent Weight True Weight
Apparent weight • measured as the reading of the scale • equal to the normal force of the scale on your feet • equal to weight for a=0
v = constant Apparent Weight NSP a = 0 WEP True Weight Elevator
a is upward Apparent Weight NSP a WEP True Weight Elevator
a is downward Apparent Weight NSP a WEP True Weight Elevator
Problem • You are riding down in an elevator carrying a 20 kg package in your arms. As the elevator gets to your floor, it slows with an acceleration of 2 m/s/s. What is the apparent weight of the package while the elevator is slowing?
a =9.8 m/s/s down NSP g WEP Elevator How large should the normal force be?
g Elevator How large should the normal force be? a =9.8 m/s/s down Apparently Weightless?? WEP
KC 135 INTERIOR