Day 59 Physics UCM LO: SWBAT perform calculate Fc and Ac LO: SWBAT Calculate Fg using NULG AGENDA Do...

Day 59 Physics UCM

LO: SWBAT perform calculate Fc and AcLO: SWBAT Calculate Fg using NULG

AGENDADo Now – Complete UCM worksheetNotesWorksheetHW22 due Thursday

Newton’s Law of Universal Gravitation

Sir IsaacNewton

(1642-1727)

Rearth

60Rearth

221

r

MMGF

Newton’s Law of Newton’s Law of GravityGravity

M1 M2

r

Constant of proportionality

Cavendish, Henry (1731-1810)

• Measured G in 1798

G = 6.67 x 10-11 Nm2/kg2

What is the force between Kiwi and a book?

4 kg

F = (6.67 x 10-11)(3)(4)

22

F = 2 x 10-10 N

221

r

MMGF

2 m

3 Kg

What is the force between Kiwi and a book?

F = (6.67 x 10-11)(3)(4)

22

F = 2 x 10-10 N

221

r

MMGF

F cat, book F book, cat

or??

1,2

4 kg3 Kg

Mearth = 5.98 x 1024 kg

r = 6.38 x 106 m

What is the force between the Earth and a book? 2

21

r

MMGF

Wearth,book = Mbook (9.8 N/kg)

Wearth,book = (6.67 x 10-11Nm2)(5.98 x 1024 kg) Mbook

(6.38 x 106 m)2kg2

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

Storey Musgrave (6 SST missions and Hubble Repair)

m = 80 kg

What’s his mass?

What’s his weight?

648 N !

Apollo 17

Earth as seen from the Moon

What is the correct orbit of the space shuttle?

What is the correct orbit of the space shuttle?

At the surface of the Earth:

rearth = 4000 miles

Wearth,Story = MStory (9.8 N/kg)

= (80 kg) (9.8 N/kg) = 784 N

400 miles above the surface :

rearth = 4000 miles

Wearth,Story = MStory (8.1 N/kg)

= (80 kg) (8.1 N/kg) = 648 N

WEP

NSP

person

Which force does the scale read?

NFS

WES

NPS

scale

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

Elevator

WEP

NSP

v = constant

a = 0

Apparent Weight

True Weight

Elevator

WEP

NSP

a is upward

a

Apparent Weight

True Weight

Elevator

WEP

NSP

a is downward

a

Apparent Weight

True Weight

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?

Elevator

WEP

NSP

How large should the normal force be?a =9.8 m/s/s down

g

Elevator

WEP

a =9.8 m/s/s down

How large should the normal force be?

g Weightless??Apparently

KC 135

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