Apparent weightlessness and all

[TyErd]

Anyone have good quick summaries for apparent weightlessness and real weightlesness all that stuff that i can chuck on my cheat sheet?

[Stroodle]

Apparent weightlessness is when the normal reaction force is zero, as apparent weight is experienced as force pushing up on us. Weightlessness is when there is no gravitational field, (like in space, far from a planet) as gravity is equivalent to acceleration.

[lachymm]

Its worth saying in apparent weightlessness questions that there is still a gravitational force acting on the individual/spacecraft/satellite

[kyzoo]

Yes, because apparant weightlessness occurs when gravity is only force acting on the object

[kenhung123]

hey in VCAA 2009 they said it was wrong for students to say normal reaction force as equal to gravitational force. Does it mean we cannot show F=mg-N (assuming weight=60kg and a=10) where 60x10=60x10-=> N=0 is not allowed?

[kenhung123]

Btw, the question was explain what is meant by apparent weightlessness

[m@tty]

I don't see how showing that helps anything really. Apparent weightlessness is based around no reaction hence can't feel weight.

[kenhung123]

Hence N=0, I'm wondering if the examiners report was implying that we cannot show N=0? What does it mean gravitational force?

[m@tty]

How is that showing n=0? You are assuming that . I think it is better to simply say that apparent weightlessness occurs when there is no reaction force and this happens when a body's acceleration is the same as its surroundings.

[kenhung123]

How is that showing n=0? You are assuming that . I think it is better to simply say that apparent weightlessness occurs when there is no reaction force and this happens when a body's acceleration is the same as its surroundings.

Alright. Thanks matty

[Chavi]

implies that the object is stationary on a flat surface.
For these 4 mark questions I'd say for full marks you need to:

1) Define Weight, Apparent Weight, Apparent Weightlessness and True Weightlessness
2) Mention that the object is in free fall, so the Normal reaction force = 0
3) Prove the N=0 using calculations
4) Add that a gravitational force, g, is still acting on the object. Thus, there is only a sensation of weightlessness (as Apparent weight is measured by the Normal force), which differs from true weightlessness where g=0 (in deep space)

[kenhung123]

So how do I should N=0?

[Chavi]

So how do I should N=0?

Net force = W - N
If Net Force = Weight, then the Normal force = 0


To understand this concept, consider yourself sitting in front of your PC/mac at time of reading, 1am. Your vertical accel = 0 (I'm assuming you're not floating up, or falling into a sinkhole ), so Net force = 0 [Newton's 2nd]. That implies that 0 = W - N, so N = W in this case, and you feel as heavy as the value for the magnitude of your normal force.

Now imagine yourself skydiving. You're falling at an accel of 9.8 m/s2, so your net force = 9.8m.
So 9.8m = W - N (and W = mg)
so N =  9.8m - 9.8m = 0.
Your normal reaction force is zero. This means that you are not in contact with any surfaces, and you feel weightless.

Hope that helps

[kenhung123]

Ah ok sounds good. So gravitational force is the acceleration and field strength is ks m/s/s?

[kyzoo]

implies that the object is stationary on a flat surface.
For these 4 mark questions I'd say for full marks you need to:

1) Define Weight, Apparent Weight, Apparent Weightlessness and True Weightlessness
2) Mention that the object is in free fall, so the Normal reaction force = 0
3) Prove the N=0 using calculations
4) Add that a gravitational force, g, is still acting on the object. Thus, there is only a sensation of weightlessness (as Apparent weight is measured by the Normal force), which differs from true weightlessness where g=0 (in deep space)

Why would you have to define true weightlessness when it asks for apparent weightlessness?