apparent weight
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How can NASA provide a sensation of weightlessness without the expense and high risk of sending astronauts into space?. Apparent Weight. Our perception of weightlessness is really the absence or reduction of normal (contact) forces acting upon our body. - PowerPoint PPT PresentationTRANSCRIPT
How can NASA provide a sensation of weightlessness without the expense and high risk of sending astronauts into space?
Apparent Weight
Our perception of weightlessness is really the absence or reduction of normal (contact) forces acting upon our body.
Conversely, we can feel heavier if the normal (contact) forces acting on us are larger than normal. Think about the forces you experienced on the Demon Drop or Power Tower at Cedar Point
Now suppose you stand on the bathroom scale and ride an elevator up and down. As you are accelerating upwards and downwards, the scale reading is different than when you are at rest and traveling at constant speed.
Apparent Weight in an Elevator
Which situation does Anna Litical feel the heaviest? Which situation does she feel the lightest?
Apparent Weight in an Elevator - Graphs
#1
#2
#3
#4
#5
#6
WT
Apparent Weight in an Elevator - Graphs
FN
Time (s)
wT
#1
#2
#3
#4
#5
#6
Apparent Weight in an Elevator - Concepts
A body at rest wants to stay at rest so when the elevator starts to move down there is less force pushing on your feet.#1
#2There is no change in motion so the upwards push on your feet must be equal and opposite to your weight
#3 Your body wants to keep moving at constant speed but the elevator is slowing down so more force is exerted on your feet
#4 The elevator is at rest so the force on your feet must be equal and opposite to your weight
#5 Your body wants to remain at rest but the elevator starts to move upwards. This imparts more upwards force on your feet than your weight
#6 Your body wants to move upwards at constant speed but the elevator slows down so there is less force on your feet
Apparent Weight in an Elevator
Coming Down - Concept FBD’s
Elevator at rest
Zero Acceleration
FNET = 0
FN = Fg
Elevator starts accelerating downwards
FNET = m a (down)
FN < Fg
Elevator is slowing down to a stop while moving down
FNET = m a (up)
FN > Fg
Elevator at constant speed downwards
Zero Acceleration
FNET = 0
FN = Fg
The normal Force (orange) is what she feels
a aFNET
FNET
Apparent Weight in an Elevator
Coming Down - Theory
FNET = 0
FN = Fg = mg
FNET = m a (down) FNET = m a (up)FNET = 0
FN = Fg = mg
a aFNET
FNET
FNET = Fg - FN
mg - FN = ma
FN = mg - ma
FN = m(g - a)
FNET = FN - Fg
FN -mg = ma
FN = ma + mg
FN = m(g + a)
Weigh normal
Weigh less
Weigh normal
Weigh more
Apparent Weight in an Elevator
Going Up - Concept FBD’s
Elevator at rest
Zero Acceleration
FNET = 0
FN = Fg
Elevator starts accelerating upwards
FNET = m a (up)
FN > Fg
Elevator at constant speed upwards
Zero Acceleration
FNET = 0
FN = Fg
Elevator is slowing down to a stop while moving up
FNET = m a (down)
FN < Fg
aa FNETFNET
Apparent Weight in an Elevator
Going Up - Theory
aa FNETFNET
FNET = 0
FN = Fg = mg
FNET = 0
FN = Fg = mg
FNET = m a (up)
FNET = FN - Fg
FN -mg = ma
FN = ma + mg
FN = m(g + a)
FNET = m a (down)
FNET = Fg - FN
mg - FN = ma
FN = mg - ma
FN = m(g - a)
Weigh normalWeigh normal
Weigh moreWeigh less