60
votes
Accepted
Cause of weightlessness
The statement in the image is shockingly wrong. Given that the Earth is visible behind the astronaut, the reduction of the gravitational force due to distance must be fairly small; on the ISS for ...
- 2,405
57
votes
Is floating in space similar to falling under gravity?
In essence, yes. Being on a space station in orbit basically IS falling due to gravity, it's just that the astronaut and the space station keep missing the Earth due to constantly moving sideways so ...
- 491
54
votes
Free fall ellipse or parabola?
The difference between the two cases is the direction of the gravity vector. If gravity is pulling towards a point (as we see in orbital mechanics), ballistic objects follow an elliptical (or ...
- 50.8k
43
votes
Accepted
How is linear momentum conserved in case of a freely falling body?
Linear Momentum is conserved only in systems with net external force equal to zero. For a body falling on Earth, it experiences Earth's gravitational force so its linear Momentum increases.
But if you ...
- 1,039
39
votes
Would weightlessness (i.e. in thrill rides, planes, skydiving, etc.) be different on a Flat Earth?
If we assume a flat disk sans gravity accelerating upwards at one $g$ (which is what the FEers propose), then the physics of thrill rides and parachutes and whatnot would actually be the same. If the ...
- 1,890
34
votes
What shape the Earth would have to be for an object in free fall to follow a straight line trajectory?
Then she asked me what shape the Earth would have to be for an object in free fall to follow a straight line trajectory. Is it even possible?
Yes, it is possible, under very strange (effectively ...
- 22.5k
31
votes
How does a virus fall down in static air?
The smaller the particle, the less effect gravity has compared with the interactions of other particles. Viruses are tiny and would (by themselves) fall incredibly slowly in air. It would be bounced ...
- 42k
27
votes
Accepted
Does a slowed down version of small stone falling in water look the same as a big rock falling in real time?
In a crude way, the answer is yes, and this effect was commonly exploited in old school sci-fi films by shooting scaled-down models and playing back the action in slo-mo.
This general effect is also ...
- 96.7k
26
votes
Does a long vertical pole fall at a different speed than a short vertical pole?
Yes. As described in the questions, there is very small difference between the acceleration of the two poles with the shorter one accelerating faster.
The difference
The gravitational force acting on ...
- 7,195
26
votes
Accepted
Does a long vertical pole fall at a different speed than a short vertical pole?
Paul T. provides a good answer regarding the case where the height of the bottoms of the poles are the same (which is what was asked for in the question). The main difference in that case is due to ...
- 634
24
votes
What do "tangential and centripetal acceleration" mean for non-circular motion?
The intent of the question is for you to resolve the acceleration into components parallel and perpendicular to the velocity vector $\mathbf v$, which you can do by definining $\hat v = \frac{\mathbf ...
- 70.5k
21
votes
Does a slowed down version of small stone falling in water look the same as a big rock falling in real time?
We can apply Dimensional analysis to answer this question.
The obvious relevant constants are
density $\rho \propto \frac{M}{L^3}$
free fall acceleration $g \propto \frac{L}{T^2}$
viscosity $\eta \...
- 744
18
votes
Is the Moon in a "Freefall" Around the Earth?
The moon is free-falling towards the earth but fortunately, the rate at which it falls to the earth is nearly equal to the rate at which the earth curves. In this answer, I will derive the formula for ...
- 7,211
18
votes
What shape the Earth would have to be for an object in free fall to follow a straight line trajectory?
An object will follow a straight line trajectory if acceleration is in the direction of its velocity. In a gravitational field, acceleration is in a fixed direction. The trajectory will be straight ...
- 42.8k
17
votes
Difference between Free Fall and Constant Velocity
The feeling of weight is just the feeling of "something" pushing on you. For example, stand in an elevator accelerating upwards, and you will feel heavier. Stand in an elevator accelerating ...
- 58.3k
15
votes
Behavior of a loose coin on a free fall ride
Suppose the penny is sitting on a thigh, and the thigh is sitting on a seat, and the seat is sitting on some shock absorber, and the shock absorber is sitting on the frame of the cart, and the ...
rob♦
- 92k
15
votes
Accepted
What does it mean that a falling mass in space doesn't sense any force?
If you've ever been in an airplane taking off or a car taking a corner fast you'll know that you can feel the acceleration. This is commonly referred to as the g-force.
In general relativity this ...
- 360k
14
votes
Accepted
How does the Equivalence principle explain "what goes up must come down"?
Clearly the apple's reference frame is non-inertial when it is on its way up, but it becomes an inertial frame when it starts free-falling downward.
In Newtonian mechanics, an object is said to be ...
- 104k
14
votes
What do "tangential and centripetal acceleration" mean for non-circular motion?
Though the path of the projectile is not a perfect circle of constant radius but at any instant of time, the path does have a radius of curvature. This radius of curvature is changing continuously for ...
13
votes
Height is compared to earth radius?
So you probably learned two equations for gravitational force, the general one being
\begin{equation}
F_g = G \frac{m_1 m_2}{r^2}.
\end{equation}
Then there is the one that we use only on earth's ...
- 145
13
votes
How does a virus fall down in static air?
Depending on the size of a particle, its motion in air under gravity can be modeled in two ways:
Air pressure difference on the two sides of the particle. This gives a terminal velocity, which is the ...
- 2,303
12
votes
Are satellites doing free fall?
May be Newton's cannonball-thought-experiment
can convince your intuition
that there is no principal difference
between a body falling down to the earth
and a satellite circulating the earth.
...
- 40.4k
12
votes
What's wrong in stating that equal gravitational forces act on two identical masses at different heights, as they have the same acceleration $g$?
The answer is that falling objects do not all accelerate towards the Earth at the same rate of $9.8 \text{ m/s}^2$.
All objects, at the surface of the Earth, accelerate the same, regardless of their ...
- 7,293
11
votes
Does a slowed down version of small stone falling in water look the same as a big rock falling in real time?
No
The water droplets have a certain size no matter the size of your stone, so if you record a small stone the water droplets will look larger relative to the stone, than if you recorded a big one.
...
- 605
11
votes
Why does gravity cause objects to pull other objects with constant acceleration and not constant force?
Imagine that you have an object of mass $M$ attracted to the earth, with the force acting on the object being $F$. You are asking if we can prove intuitively why $F$ should be proportional to $M$ - i....
- 2,837
10
votes
Is the Moon in a "Freefall" Around the Earth?
The moon is falling towards but "missing" Earth. Had it no sideways motion, it would certainly just fall straight down and crash. So yes, you can say that.
- 51.7k
10
votes
Difference between Free Fall and Constant Velocity
In the two situations, the astronauts feel "weightless" and are "floating" in the same way. However the two situations are very much different in terms of forces and acceleration. ...
- 105k
10
votes
Behavior of a loose coin on a free fall ride
Firstly, you would not need to rely on some random small twitch.
The coin, in resting on the flesh of the thigh in the pre-launch phase, is causing some elastic compression of the skin. Upon launch, ...
- 10.8k
Only top scored, non community-wiki answers of a minimum length are eligible