63
votes
If the ground's normal force cancels gravity, how does a person keep rotating with the Earth?
Actually, this is rather insightful. The normal force from the ground does not quite cancel out the effect of gravity. The difference between them is precisely the centripetal force that keeps you ...
- 77.3k
59
votes
Accepted
How can the centripetal force lead to objects flying apart?
In the lab frame of reference, you need to reverse the question - don't ask yourself what pulls the particles apart but what keeps them together.
By Newton's laws, everything on which no force acts ...
- 129k
58
votes
Accepted
What is the reason behind water not falling from a bucket at the top of loop?
It is a common misconception that objects have to move in the direction of the force. This is false; the acceleration points in the direction of the force. This means the change in velocity points in ...
- 58.6k
57
votes
What is the reason behind water not falling from a bucket at the top of loop?
The water does fall. It just doesn't fall faster than the bucket. By pulling on the bucket, you keep it around the (also falling) water.
- 42.3k
44
votes
Accepted
If an object moving in a circle experiences centripetal force, then doesn't it also experience centrifugal force, because of Newton's third law?
This is a common misinterpretation of Newton's third law, often stated as "to every action, there's an equal and opposite reaction." As you surmise, "action" and "reaction" refer to forces. However, ...
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41
votes
Why is acceleration directed inward when an object rotates in a circle?
As a rule of thumb: when somebody states that something is obvious you should really doubt everything he says. Especially if he is an ex navy seal :)
Think about the ball moving in circle: Newton's ...
- 4,635
39
votes
Accepted
For a spacecraft orbiting a planet, orbital speed is inversely proportional to orbit radius. But speed must be increased to increase orbit radius?
The equation you have written there applies only for circular orbit but the orbit is not circular during the time the spacecraft is climbing to higher orbit. As the spacecraft climbs towards the ...
- 818
38
votes
Accepted
If centrifugal force is a pseudo-force then why we can observe its effects outside of rotating frame?
When objects fly off a spinning table, from an external reference frame they simply stop travelling in circles. At the point of "unsticking" they do not accelerate radially outwards from the centre of ...
- 7,528
36
votes
Why is acceleration directed inward when an object rotates in a circle?
You can't push rope.
Intuitively, rope is only useful under tension and not compression - you can pull an object with a rope, but not push it. It should be obvious that when you swing a ball on a rope,...
- 10.4k
34
votes
Accepted
How is angular momentum conserved for the orbiting body if the centripetal force disappears?
If the Sun were to magically disappear then the Earth would fly off at a tangent to its orbit. The trajectory would look like this:
The green dot shows the position of the Earth at the instant the ...
- 363k
30
votes
Why do we still use pseudo forces?
In practice, in newtonian mechanics, pseudoforces are used, because they're simple and convenient.
At the end of the day, they're only inertial terms that you're "disguising" as forces. You ...
- 6,269
22
votes
How can the centripetal force lead to objects flying apart?
Try to imagine, instead of a big stone, a big plate. On top, you fill the plate with sand. Now you start spinning the plate.
What's going to happen to the sand? The sand is going to leave the plate ...
- 587
21
votes
Accepted
How is linear momentum conserved in circular motion?
Your confusion lies in the way you configured the problem. Let two charged particles revolve around the center of the system. It's quite clear in that viewpoint that any change in linear momentum of ...
- 51.7k
21
votes
Accepted
If you're holding on to a playground spinning wheel and then let go, is your trajectory straight or curved?
A child on a playground wheel normally rotates once per revolution of the wheel, as seen from the ground. If the child lets go, they will move in a straight line, but will continue to rotate at the ...
- 3,166
20
votes
Accepted
How exactly does artificial gravity work?
If you were in a zero-gravity environment (e.g., in earth orbit or in a coasting trajectory en route to Mars), alone in your space suit, you would feel no gravity.
If a big pipe were placed around ...
- 25k
20
votes
Can a bullet travel all the way around a centrifuge?
I decided to simulate the flight of the bullet, including air resistance, in Mathematica. In a rotating reference frame, the equation of motion for the bullet is
$$
m \vec{a} = -\frac{1}{2} \rho C_d ...
- 51.6k
19
votes
Accepted
What if the net force provided for a circular motion is larger than the required centripetal force?
Let's be more exact about this:
Newton's second law for planar motion in polar coordinates is given by
$$\mathbf F=m\left(\ddot r-r\dot\theta^2\right)\hat r+m\left(r\ddot\theta+2\dot r\dot\theta\right)...
- 58.6k
18
votes
Accepted
How does an object undergoing circular motion increase its tangential velocity?
In the case that you describe, an individual swinging a mass horizontally on the end of a string, the string does not run directly to the centre of rotation. Instead, it runs to your hand, which in ...
- 10.8k
18
votes
Accepted
Confusion about components of circular motion
Your question is interesting because it shows the dangers of working with infinitesimals without a careful control of their meaning.
Basically, your question is applicable to any motion, when the ...
18
votes
Why is acceleration directed inward when an object rotates in a circle?
I would explain the correct answer without reference to forces. Basically, this is a question about acceleration and I would not introduce forces or another reference system. in addition to the one ...
17
votes
If the ground's normal force cancels gravity, how does a person keep rotating with the Earth?
You say
If there is no centripetal force
But that is not true. When you measure your weight at the North Pole or at the Equator, you get a different answer. The shape of the Earth (a slightly ...
- 119k
17
votes
Accepted
When a ball on a rope swings in a circle, is there both centripetal force and tension force?
The centripetal force can be made up of any type of force, whether gravitational, friction or tension. The centripetal force is not a force type, it is just a net force that is always radial. So it is ...
- 877
17
votes
Accepted
What would happen to the moon if we reduce its tangential velocity slightly?
No, the moon will not eventually fall to earth. Reducing the tangential velocity by a small amount will affect the orbital trajectory of the moon. Since the path followed by the moon is already ...
- 2,382
17
votes
Is there jerk on Uniform Circular Motion?
Jerk is the change in acceleration. If acceleration is changing, then there is jerk. Since there is a changing acceleration in circular motion, there is jerk in circular motion.
I'm not entirely ...
- 51.7k
17
votes
For a spacecraft orbiting a planet, orbital speed is inversely proportional to orbit radius. But speed must be increased to increase orbit radius?
A simple way to calculate moving from one circular orbit to a larger one: Start by increasing the speed. The orbit becomes an ellipse. As Kirby points out, the speed decreases as the satellite moves ...
- 12.2k
15
votes
How can the centripetal force lead to objects flying apart?
You don't have to explain this by centrifugal force, or any fictitious force at all. All what centrifugal force is about is inertia.
As your stone is spinning, it has some velocity. But since ...
- 29.6k
14
votes
Accepted
Why, when we calculate forces in banking of roads, we do not take the centripetal force but the centrifugal force?
Define the "outward" direction in your diagram (to the left) to be the positive $x$-direction, and define the vertical direction to be the $y$-direction.
In the inertial reference frame, ...
- 51.6k
13
votes
What would happen to the moon if we reduce its tangential velocity slightly?
No, not for any amount that could reasonably be called "slight".
The thinking error I see here is that I believe what you are imagining happening is the Moon to start "spiraling out of orbit", like a ...
- 20.8k
13
votes
Is centripetal acceleration almost perpendicular to velocity or it is exactly perpendicular to velocity?
Is there something missing in my reasoning ?
Yes. You are treating the velocity as though it were constant over a finite time and it is not. The velocity varies over time and can only be treated as ...
- 109k
13
votes
Can a bullet travel all the way around a centrifuge?
I think you're right that atmospheric effects are an issue. This is easiest to see if you picture the situation in a non-rotating reference frame.
In that case, just after the bullet is fired it is ...
- 34.9k
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