A tag for questions about rotational motion, including angular velocity and angular acceleration.
Questions tagged [rotational-kinematics]
1349 questions
31
votes
3 answers
Will a falling rod stay in contact with the frictionless floor?
Question
A uniform rod of mass $M$ is placed almost vertically on a frictionless floor. Since it is not perfectly vertical, it will begin to fall down when released from rest.
I have seen solutions online for this problem and while solving this…
Ajay Mohan
- 1,441
29
votes
3 answers
Why does a bowling ball roll down faster on a slope than a tennis ball, yet both hits the ground at the same time if they're dropped from the rooftop?
If a tennis ball and a bowling ball are dropped of a rooftop, they hit the ground at the same time. But if they are rolled down a slope, the bowling ball rolls faster. Why?
Tim Verboomen
- 307
29
votes
8 answers
Why is the moment of inertia (wrt. the center) for a hollow sphere higher than a solid sphere (with same radius and mass)?
Why is the moment of inertia (wrt. the center) for a hollow sphere higher than a solid sphere (with same radius and mass)? I have completely no idea and I am inquiring about this as it is an interesting question that popped in my head while doing…
Jossie
- 557
26
votes
7 answers
How is it that angular velocities are vectors, while rotations aren't?
Does anyone have an intuitive explanation of why this is the case?
Casebash
- 2,804
25
votes
6 answers
Conical train wheels
I've been reading about how the conical shape of train wheels helps trains round turns without a differential. For those who are unfamiliar with the idea, the conical shape allows the wheels to shift and slide across the tracks, thus effectively…
Rations
- 652
24
votes
8 answers
A simple derivation of the Centripetal Acceleration Formula?
Could someone show me a simple and intuitive derivation of the Centripetal Acceleration Formula $a=v^2/r$, preferably one that does not involve calculus or advanced trigonometry?
Conceptuality
- 403
23
votes
3 answers
Can the direction of angular momentum and angular velocity differ?
While studying rotational mechanics, I came across a section where it mentioned that angular momentum may not necessarily be parallel to angular velocity. My thoughts were as follows:
Angular momentum ($L$) has the relation $L=I\omega$ where…
Physicsapproval
- 585
21
votes
6 answers
Can the average length of the day and night of a planet be different?
At one point in "Marvel's Agents of S.H.I.E.L.D.", some agents are on a planet where the day, defined as the length of time where the sun shines on the planet, occurs only once every 18 years for a couple hours.
Is that a plausible scenario? Can the…
solalito
- 328
19
votes
3 answers
Does the top of a wheel really move at twice the velocity of the center?
According to the physics of a wheel rolling without slipping, the topmost point moves twice as fast as the wheel.
But I tried an experiment:
Take a wheel on a table and hold a ruler horizontally in contact with the top of the wheel. Roll the wheel…
Manukrishnan P
- 311
18
votes
3 answers
Direction of angular velocity
Angular velocity is the rate of angular displacement about an axis. Its direction is determined by right hand rule.
According to right hand rule, if you hold the axis with your right hand and rotate the fingers in the direction of motion of the…
Rafique
- 1,199
17
votes
10 answers
Formula for centripetal acceleration: simple proof that does not use calculus?
I teach physics to 16-year-old students who do not know calculus and the derivates. When I explain the formula for centripetal acceleration in circular uniform motion, I use this picture:
Here,
$$\vec{a}_{\text{av}}=\frac{\Delta \vec{v}}{\Delta…
Sebastiano
- 2,681
17
votes
3 answers
Do mankind and manmade activities/constructions have any effect on the rotation of the Earth?
We walk or ride on our vehicles to our destinations daily. Does our movement have any effect on the rotation of the earth according to Newton's law? What will be the effect if we move all the peoples along with their vehicles at their maximum…
Deiknymi
- 2,271
16
votes
6 answers
How can the angular velocity vector be obtained from angular displacement which is not a vector?
My physics book (The Fundamentals of Physics) while explaining vector-ness of angular quantity (formally "Are Angular Quantities Vectors?") states that angular velocity and angular acceleration are vectors. But the turning point comes when it talks…
user249968
15
votes
5 answers
If I jump, would I be displaced from my initial position since the Earth is moving?
If I jump and stay in the air for a long enough time, will my position be changed since the Earth is rotating?
neofyt
- 357
15
votes
6 answers
Rotate a long bar in space and get close to (or even beyond) the speed of light $c$
Imagine a bar
spinning like a helicopter propeller,
At $\omega$ rad/s because the extremes of the bar goes at speed
$$V = \omega * r$$
then we can reach near $c$ (speed of light)
applying some finite amount of energy
just doing
$$\omega = V /…
Hernan Eche