1. How can NASA provide a sensation of weightlessness without the expense and high risk of sending astronauts into space?

2. Weight vs Apparent Weight The force of gravity (Fg or F or F ), like any force causes acceleration. Although we tend to think it only pulls us toward the center of the Earth. That ‘pulling’ we feel as weight. But being weightless (like an astronaut is NOT the absence of gravity, rather the absence of F_____ An example is a car going over a hill, or an amusement park ride Your weight feels different when you accelerate

3. Apparent Weight
Our “feeling” 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.

4. Apparent Weight in an Elevator
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.
Which situation does Anna Litical feel the heaviest? Which situation does she feel the lightest?

5. Apparent Weight in an Elevator
Coming Down – Net Force
FNET a a
FNET
Elevator starts accelerating downwards
FNET = ma (down)
FN < Fmg
Elevator at rest
Zero Acceleration
FNET = 0
FN = Fmg
Elevator at constant speed downwards
Zero Acceleration
FNET = 0
FN = Fmg
Elevator is slowing down to a stop while moving down
FNET = Fma (up)
FN > Fg
The normal Force (orange) is what she feels

6. Apparent Weight in an Elevator Going Up - Concept FBD’s
FNET
FNET
Elevator starts accelerating upwards
FNET = ma (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 = ma (down)
FN < Fg
Elevator at rest
Zero Acceleration
FNET = 0
FN = Fg

7. Answer the questions

8. Homework Problem #5

9. 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
There is no change in motion so the upwards push on your feet must be equal and opposite to your weight #2 #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