All Questions
Tagged with motion or kinematics
4,321 questions
4
votes
1
answer
451
views
Kinematics textbook illustration
I have trouble interpreting this illustration. I see why r (position) and a (acceleration) are the way they are, but what happened to v? Why is it smaller than its coordinates? Is this another error ...
- 53
1
vote
1
answer
335
views
Simple kinematics excercise, throwing something upwards [closed]
I am trying to solve this simple excercise:
Question
You throw a small coin upwards with $4 \frac{m}{s}$ . How much time does it need to reach the height of $0.5 m$ ? Why do we get two results?
...
- 53
33
votes
14
answers
85k
views
Recommendations for good Newtonian mechanics and kinematics books
What are some good books for learning the concepts of Kinematics, Newton laws, 2D Motion of Object etc.?
2
votes
2
answers
3k
views
Projectiles problem solving
I've only learned about to use kinematics equation when solving projectile problems but today i came across the following equations. where does they come from?
Distance travelled
Time of flight
Angle ...
user2296
4
votes
3
answers
491
views
Object docking in Space
How do objects dock in space?
There's a recent piece of news that Keppler would dock to the ISS sometime this week. I want to know the operational aspects of it - considering the velocity of the ...
- 41
6
votes
3
answers
2k
views
Does entropy apply to Newton's First Law or does "acted upon" always require an external factor?
First law: Every body remains in a state of rest or uniform motion (constant velocity) unless it is acted upon by an external unbalanced force. This means that in the absence of a non-zero net force, ...
- 161
4
votes
5
answers
55k
views
Stopping Distance (frictionless)
Assuming I have a body travelling in space at a rate of $1000~\text{m/s}$. Let's also assume my maximum deceleration speed is $10~\text{m/s}^2$. How can I calculate the minimum stopping distance of ...
-1
votes
5
answers
4k
views
2 balls falling hit the ground at the same time
There are 2 balls in a vacuum, next to each other but not touch. They are on the edge of a surface they will both leave the table at exactly the same time. One gets pushed harder than the other. The ...
- 6,987
3
votes
3
answers
2k
views
Negative vectors (e.g. velocity)
If you said someone had a velocity of $-12\,{\rm mph}$ and they were traveling north? Wouldn't it mean that they were traveling $12\,{\rm mph}$ south?
This is a quote from here:
if something [...
- 6,987
1
vote
1
answer
6k
views
Solving straight-line motion question for time [closed]
I apologise in advance if this question doesn't appeal to the advanced questions being asked in this Physics forum, but I'm a great fan of the Stack Exchange software and would trust the answers ...
- 113
0
votes
1
answer
219
views
Kinematics of scratching a rolling tire
Recently a "U" shaped scratch appeared on my car's front tire. It looks like someone rolled past a curb and scraped it. This has led me to the following problem:
Generate a plot (ideally polar) of a ...
- 101
3
votes
2
answers
1k
views
How much does it cost every time your car stops for a traffic light?
Every time we have to stop the car, it is costing us extra money, because we have to then accelerate to full speed again. I would like to know how much.
In order to simplify the situation, we can ...
- 387
3
votes
5
answers
6k
views
Are all objects in motion?
It seems like everything in the universe is in motion, at least relative to some other object. That leads me to believe that all objects are in motion. But how do we measure motion when we are ...
- 384
1
vote
1
answer
312
views
Is there a theory about kinetic energy "particles"? [closed]
We have a model of electricity which says electrons flow from one place to another. We have a model of optics which says that photons go from one place to another. As I understand, there is currently ...
- 625
6
votes
2
answers
7k
views
Is there a 2D generalization of the coefficient of restitution?
The coefficient of restitution characterizes a collision in one dimension by relating the initial and final speeds of the particles involved,
$$C_R = -\frac{v_{2f} - v_{1f}}{v_{2i} - v_{1i}}$$
In a ...
- 77.3k
92
votes
15
answers
193k
views
What is the difference between "kinematics" and "dynamics"?
I have noticed that authors in the literature sometimes divide characteristics of some phenomenon into "kinematics" and "dynamics".
I first encountered this in Jackson's E&M book, where, in ...
- 9,631
0
votes
6
answers
3k
views
Is it possible to throw an object faster but over the same distance?
Is it possible to throw say a tennis ball at $1ms^{-1}$ for 20m and then be able to throw the same ball at $2ms^{-1}$ for 20m at the same angle? That is throwing the ball in a traditional curve withe ...
- 6,987
310
votes
18
answers
85k
views
Why does kinetic energy increase quadratically, not linearly, with speed?
As Wikipedia says:
[...] the kinetic energy of a non-rotating object of mass $m$ traveling at a speed $v$ is $\frac{1}{2}mv^2$.
Why does this not increase linearly with speed? Why does it take so ...
- 3,235
1
vote
4
answers
5k
views
4th kinematic equations for constant acceleration
Ive been given the 4 kinematic equations for constant acceleration. The fourth being:
$$s=ut+\frac{1}{2}at^2.$$
If rearranged it forms the quadratic equation
$$at^2+2ut-2s=0.$$
But that means that ...
- 6,987
3
votes
3
answers
3k
views
Distance travelled in free-fall
When an object is in free fall, we have:
$$a(t) = g - \frac{c}{m}v(t)^2$$
where $g$ is acceleration due to gravity, $m$ is the mass of the object, and $c$ is the coefficient of air resistance.
How ...
- 133
9
votes
6
answers
250k
views
Why is this calculation of average speed wrong? [closed]
A person drove 120 miles at 40 mph, then drove back the same 120 miles at 60 mph. What was their average speed?
The average of the speeds is
$$\frac{40\ \text{mph} +60\ \text{mph}}{2} = 50\ \text{...
- 349