All Questions
Tagged with kinematics classical-mechanics
31 questions
12
votes
2
answers
16k
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Understanding terms Twist and Wrench
In kinematics, physics and especially robotics, we often encounter the terms Twist and Wrench. Twist is (LinearVelocity, AngularVelocity) and Wrench is (Force, Torque). The reason I'm confused is I ...
- 505
7
votes
4
answers
3k
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Is there a formula that gives the position of an object depending on the time, but which doesn't allow the object to surpass the speed of light?
I have found these two formulas:
$v = at + v_0$
$x = \frac{1}{2}at^2 + v_0t + x_0$
a is the acceleration
v is the velocity
x is the position
t is the time
$v_0$ is the initial velocity
$x_0$ is the ...
- 1,643
3
votes
2
answers
4k
views
Elastic collision between two circles [duplicate]
I am trying to calculate the final velocities of two equal mass 2-dimensional circles after an elastic collision. I have tried to figure it out using formulas I know from high school physics, but ...
user99752
30
votes
4
answers
73k
views
Difference between momentum and kinetic energy
From a mathematical point of view it seems to be clear what's the difference between momentum and $mv$ and kinetic energy $\frac{1}{2} m v^2$. Now my problem is the following: Suppose you want to ...
- 1,191
5
votes
2
answers
1k
views
The Double Integrator: Matching velocity and position as quickly as possible with only a limited amount of force available
If a body with mass $m$ begins at position $x_0$ with velocity $v_0$ and experiences a force that varies as a function of time $f(t)$ (and we ignore gravity, friction, and everything else that might ...
- 375
8
votes
4
answers
3k
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Why does a ping pong ball change direction when I spin it on a table?
When I spin a ping pong ball on the table, it rolls forward in the opposite direction of the spin, and then eventually changes direction and rolls backward.
Here's a video demonstrating the effect.
...
- 183
18
votes
5
answers
605
views
Does the mass point move?
There is a question regarding basic physical understanding. Assume you have a mass point (or just a ball if you like) that is constrained on a line. You know that at $t=0$ its position is $0$, i.e., $...
- 181
1
vote
1
answer
450
views
Is a reasonable assumption to consider that the contact point of the Euler's Disk (with stationary center of mass) trace this finite bounded spiral?
Is a reasonable assumption to consider that the contact point of the Euler's Disk (with stationary center of mass) trace this finite bounded spiral?
This question is highly related to working with the ...
- 103
2
votes
3
answers
246
views
Why does this example seem to contradict conservation of energy?
Consider a 10 kg box on the bed of a truck accelerating at 1 m/s^2. Consider a reference frame where it starts at 0 m/s and ends at 10 m/s and then consider a reference frame where it starts at -5 m/s ...
- 392
7
votes
2
answers
2k
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What is the highest energy position for a double pendulum? And for which energy positions is it chaotic?
Math/physics teachers love to break out the double pendulum as an example of chaotic motion that is very sensitive to initial conditions. I have some questions about specific properties:
For a ...
- 195
7
votes
4
answers
633
views
Speed resulting from tangentially applying force to solid spheres with different mass distributions
Given are two solid spheres of the same size and weight. They both have their center of mass at their geometric center.
One of them (A), however, has most of its ...
- 133
6
votes
2
answers
17k
views
Is a heavier skier faster? [duplicate]
Is it true that a heavier skier goes faster? If it is, why is that?
My intuition would be that the speed gained by a skier should be independent from its mass, since both its acceleration and the ...
3
votes
2
answers
254
views
In Uniform Circular Motion, why does the normal accelaration not increase the magnitude of velocity?
This very simple question was posed by a high-school student in the class.
Consider a particle going in a uniform circular motion (uniform implies that the speed is constant). We know that there is a ...
- 661
2
votes
3
answers
521
views
What is really instantaneous?
How can a body travel at an instant and what does instantaneous speed tells us?
What really is meant by speed of an object at an instant if an object does not travel at an instant? I would like a ...
- 317
1
vote
2
answers
2k
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Conservation of linear momentum magnitude along a trajectory
I was once criticized for "taking angular momentum as momentum going
in a circle". I was loosely trying to state, in classical mechanics,
that in using conservation of momentum, one can switch between ...
- 3,808
0
votes
2
answers
244
views
Why is the direction of net force on an object and the direction of acceleration of that object different in this problem?
A $ 2.0 kg $ box of cucumber extract is being pulled across a frictionless table by a rope at an angle $ \theta=60° $ (from positive direction of $ x $ axis, we have taken horizontal surface of table ...
5
votes
3
answers
3k
views
Does more rain strike a vehicle while moving or while stopped (or neither)? [duplicate]
Assume there is a rainstorm, and the rain falling over the entire subject area is perfectly, uniformly distributed. Now assume there are two identical cars in this area. One is standing still, and ...
- 251
4
votes
3
answers
69k
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Difference b/w Kinetics & Kinematics w/concrete example
(I know whether I understand this or not doesn't matter much to my work & study but am just curious.)
I still can't differentiate in my head kinetics and kinematics (similar thread is found but ...
- 143
4
votes
1
answer
780
views
Is Centripetal Velocity a Thing?
I'm quite new to physics so this question may sound dumb for many of you. But when I was learning about uniform circular motion, all sources I can find talks about centripetal acceleration, and, when ...
- 143
2
votes
1
answer
167
views
What is the relationship between the speed of the end of the thread and the angular velocity of the spool which was pulled by the winding thread?
On a rough ground, there is a cylindrical spool of inelastic thin thread (as the picture following), the inner and outer radii are $r$ and $R$ respectively, the thin thread is wound in its inner ...
- 363
2
votes
0
answers
183
views
Proving that the relative angular velocity of any particle with respect to any other particle is the same in a rigid body
Claim: The angular velocity of any point mass of a rigid body relative to any other point mass is the same, i.e., $\vec{\omega_{i,j}} = \vec{\omega}\;\,\forall{i}\,\forall{j}$, where $\vec{\omega}$ is ...
- 41
2
votes
2
answers
2k
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Why doesn't the optimal angle (for maximum range) on an inclined plane equal 45 degrees?
Observe this case
The goal is to maximize $d$ by increasing the angle of the initial velocity. Since we know that the range is maximum for $\theta=45^\circ$ I would reason that the jumping ramp has ...
- 332
2
votes
4
answers
1k
views
Uniform Circular Motion w/ Tension and Friction
So I had a problem today which I couldn't make any sense of. I don't have access to it at the moment but this is a pretty accurate approximation.
Basically, a mass (m) is swinging horizontally on ...
- 21
1
vote
5
answers
7k
views
Optimum launch angle for a projectile launched from a height above the ground [closed]
If a projectile is launched from a height greater than zero and landed to a height equal to zero, is the optimum launch angle that gives the greatest horizontal range still $45$ degrees or not?
I know ...
user282164
1
vote
2
answers
153
views
Acceleration: Value Disparity?
If we consider a ball moving at an acceleration of $5\ \mathrm{m\ s^{-2}}$, over a time of 4 seconds, the distance covered by the ball in the first second is $5\ \mathrm m$. In the 2nd second will $5\ ...
- 383
1
vote
1
answer
151
views
Angular velocity by velocities of 3 particles of the solid
Velocities of 3 particles of the solid, which don't lie on a single straight line, $V_1, V_2, V_3$ are given (as vector-functions). Radius-vectors $r_1, r_2$ from third particle to first and second ...
- 113
0
votes
2
answers
60
views
When does a free body moving on a smooth circular path make a complete revolution?
If we have a body like the one below , What will be the minimum initial velocity $V_0$ to complete one revolution, My assumption was that it has to reach $\theta=180$ ,But how do I describe this ...
0
votes
1
answer
87
views
A pearl that moves in a smooth vertical hoop (Circular motion) [closed]
I couldn't understand something about the situation of a pearl that moves in a smooth vertical hoop in circular motion.
When the normal force equals 0 , the pearl didn't disconnect from the smooth ...
- 407
-2
votes
1
answer
97
views
When one kid runs into another and they bump heads, why is the slowest mover in most pain? [closed]
In my experience, if one kid runs really fast and accidentally bumps into a second kid who's standing still, and they bump heads, the kid who was 'standing still' (relative to earth) always seems to ...
- 613
-4
votes
1
answer
69
views
Is it possible for a point-like system to behave like $x(t) = \frac{t}{2}\log(t^2)$ near $t=0$? (infinite speed) [closed]
Is it possible for a point-like system to behave like $x(t) = \frac{t}{2}\log(t^2)$ near $t=0$? (infinite speed)
I know beforehand that relativity theory forbids anything with mass from travel faster ...
- 103
-13
votes
3
answers
3k
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What would happen if an unstoppable force hits an immovable object? [closed]
I realize that the question a rather large paradox, but I do wonder if such a thing were true what would happen, assuming that neither of these "objects" can be destroyed by each other?
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