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Weight

Floating Cannon Ball

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"Why can mercury make a cannon ball float?"

"Mercury must be  more dense than the steel cannonball"

Weight - net gravitational force on an object

g = acceleration due to gravity

Earth: g = 9.8 m/s²

Moon: g = 1.6 m/s²

Apollo 11 astronaut Edwin Aldrin stands near the leg of the lunar module on the Moon. Despite the fact that the backpacks and astronauts only weighed 1/6 on their 350 pound Earth weight, their center of gravity was shifted so they had to lean slightly forward to balance. Footprints are clearly visible in the foreground.

(Apollo 11, AS1140-5902)

slope = g

Mass - amount of matter an object possesses

Weightless
Not Massless!

What is the relationship
between mass and distance?

Choice 1
Mass is not affected by distance (only weight)

1 kg  ≈ 2.2 lbs

University of Michigan

1 lbs  ≈ 5 N

Average Senior Weighs

120 lbs ≈ 600 N

Finding acceleration due to gravity using weight

Ex) A satellite having a mass of 25. kg experiences a gravitational force of 200 N. Find the acceleration due to gravity at this location.

g = 200 N/25 kg

a  = 8 m/s²

or 8 N/kg

Ex) A rocket weighs 18,000 N at the earth's surface. If the rocket rises to a height where its distance from the earth is 3 earth radii, its weight will be ...

When an object is on the earth,
it is one earth radius away.

Distance from earth to rocket triples so, ....

(original weight, 18,000 N)

Galaxy Formation
Computer Simulation - NASA

NASA