The description of the movement of bodies by their position, velocity, acceleration (and possibly higher time derivatives, such as, jerk) without concern for the underlying dynamics/forces/causes.

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Explanation about friction force directions of two moving bodies in contact

can someone explain me why in this scenario (picture below) we have a friction force Ftr12 in the same direction as movement (left part of the picture, case 1 ) and how these directions of friction ...
4
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2answers
286 views

Projectile motion maximum distance to origin

Is there an elegant or easy way to derive the maximum distance from the origin to a point of the parabola created by projectile motion (assume initial position is the origin)? Other than ...
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2answers
121 views

Orientation of a rocket going in a circle?

This problem is from my physics homework: A rocket is moving at constant speed in a perfect circle in deep space, far away from any planets or stars. The diagram below shows the circle the ship ...
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3answers
89 views

Difference between $|d{\bf r}|$ and $d|{\bf r}|$

What is the difference between $|d{\bf r}|$ and $d|{\bf r}|$ and why are both of them not always equal to each other? My question might seem stupid to some and will probably get downvoted but I have ...
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2answers
149 views

Which point in the graph does a parachute open?

The diagram represents speed-time for a sky diver. He falls freely from an aircraft then opens a parachute and later lands safely on the ground. At which point did the parachute fully open? ...
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3answers
5k views

Proof of centripetal acceleration formula ($a_c = v^2/r$) for non-uniform circular motion

The formula for centripetal (radial) acceleration is well known, and there exist many proofs for it: $$||a_c|| = \frac{||v||^2}{r}$$ However, all the proofs I've seen rely on the fact that it is ...
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1answer
181 views

Finding the total energy in centre of mass frame

I'm working through a problem in a special relativity textbook (Woodhouse) and I'm having some difficulty. I have to show that if I have a particle of rest mass $M$, total energy $E$ colliding with a ...
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1answer
95 views

Kinematics equations of motion find x position in 2D from height

I have a question and I thought of 2 possible ways to answer it however the resulting answers are different which means I must be doing something wrong in my calculations. All the below happens 2 ...
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1answer
385 views

The dimensional formula of distance travelled in $n$th second

I read that the dimensional formula of distance traveled in $n^{th}$ second is same as that of velocity. Okay, the formula for the distance traveled in $n^{th}$ second is $s_t= u+\frac{a}{2}(2t-1)$ ...
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2answers
72 views

Kinetic friction with no force on an object

We've learnt that friction is the opposition of motion and that friction appears the instant a force is applied on an object i.e when an object is at rest (with no force acting on it) then there is no ...
-1
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1answer
39 views

For a projectile to cover maximum vertical distance in the least time, what will be the angle of projection? [closed]

My first guess was 90° as there is no horizontal component for velocity when the angle is 90°. But I could not prove it mathematically (and also I'm not sure if it is really 90°).
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1answer
38 views

Question to find distance at which 2 trains will pass each other [closed]

I was solving some questions related to motion, and I came through a question which I cant understand. The question goes like this: Two trains A and B, 100 km apart are approaching towards each ...
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2answers
101 views

Is there a situation where $\left|d\vec{v} / dt\right|$ is non-zero while $d|\vec{v}| / dt$ is zero?

Here $\vec{v}$ represents velocity and $dv / dt$ gives the instantaneous acceleration. $|\vec v|$ gives the magnitude of velocity. When acceleration is zero, then change in magnitude of velocity is ...
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2answers
196 views

Ball flying towards me - Newton's third law is violated?

I was trying to answer the question of the flying ball here on the basis of Newtons third law and Momentum conservation. Here is what I have tried. Lets take $m_1$ (the ball) hits $m_2$ (the man). ...
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2answers
88 views

Area under v-t and a-t graphs

I know that the magnitude ( i.e. considering all area as positive) of area under v-t graph gives distance travelled by the particle in the given time. But I've been told that magnitude of area under ...
0
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1answer
30 views

Calculate constant acceleration for a length of track with start at rest and final velocity known [closed]

My maths and physics are rusty... I'm a bit ashamed, but I have this problem: Let's have a 1000m linear accelerator (mass driver) propel a payload at constant acceleration, with a final velocity of ...
2
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1answer
40 views

Lorentz-invariant phase space of a three-body decay process

I am not following the use of delta function in the 3-body decay process. In $\gamma^* \to gq\bar{q}$ process, with $\gamma^*$ being a virtual photon, we have a phase space factor $$d^9R_3 = ...
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1answer
324 views

Tangential and radial acceleration in projectile motion

I'm currently learing kinematics, specifically projectile motion and as an example in my textbook is a bullet fired at some angle. I understand the derivation of formulas to describe that motion and ...
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2answers
736 views

What stops giant cruise ships toppling over in rough seas?

A week ago, 2 of the most gigantic cruise ships in the world docked near my city. If you have seen one, or been on one, you will know how large they are. They look extremely unsafe to me, although ...
2
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7answers
552 views

Free fall into circular motion

If I'm on a roller coaster free falling from height $h$ and then suddenly start going into horizontal motion with a radius $r$ of turn what is the $g$-force I experience? I worked out the equation ...
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3answers
122 views

Isn't a physical frame of reference useless for calculating speed? [closed]

Please ignore relativistic effects and the effects of the expansion of space-time due to the expanding universe theory for the purposes of this question. Whenever someone asks what is the speed of X, ...
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2answers
871 views

How can an object move from point A to point B?

If I was at point $A$ and I wanted to walk directly to point $B$, I would have to walk half way to point $B$, but before that I would have to walk half way to halfway to halfway to point $B$ and half ...
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1answer
305 views

Is it possible to determine particles' velocities from their crossings on a ring?

2 particles are constrained to move in a ring. Both particles begin moving at $t=0$ from $p=0$, each particle moving in the opposite direction of the other. It is known that they are moving at ...
4
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5answers
448 views

Intuitive answer to a kinematic problem

The problem: Two particles A and B start from rest and move for equal time on a straight line. The particle A has an acceleration a for the first half of the total time and 2a for the second half. ...
5
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2answers
159 views

Extra vibrational mode in linear molecule

When calculating the number of vibrational modes for a molecule, the formulas differ for linear $(n = 3N - 5)$ and non-linear $(n = 3N - 6)$ molecules, where $n$ is number of modes and $N$ is number ...
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3answers
67 views

How to apply Newton's first law to moving object?

I'm new to many forces, such as gravity and friction, and I don't really know how they work. I'm trying to simulate a ball bouncing with a program, and it travels at a constant speed horizontally. I ...
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1answer
31 views

A way to determine if a body accelerates or loses speed at a certain time

With given vectors for acceleration and velocity, is there a way to determine if a body accelerates or decelerates at a certain time-interval? Can this be determined, for instance, by simply observing ...
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17answers
25k 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.?
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0answers
33 views

irreversibility Aristoteles law of motion

I am watching the second lecture from the theoretical minimum and do not understand the argumentation of Susskind. For those who do not want to watch the video. It is about the law of motion from ...
9
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3answers
1k views

Do you encounter more photons (per unit time) when moving forwards at a constant velocity?

Let's say you have rain hitting you evenly on all sides (not very realistic, I know). If you were to move forwards at a constant speed, there would be more droplets of rain hitting you per second on ...
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3answers
110 views

Question about rain when an object is moving

So here's the question: A train window is 1 meter high and 10 meters long. A raindrop rolls down the window at a vertical speed of 5 meters per second(when stationary). If the train is moving at 30 ...
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0answers
51 views

Compute distance travelled based on a yaw-rate

Assume that a rigid body is traveling with constant velocity $v$, and (this rigid body) is rotating with a constant yaw rate of $\dot{\theta}$. Find the distance travelled in one time step, $\Delta ...
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1answer
38 views

Relative motion with two observers

For four particles A, B, C, D , the velocities of one with respect to other are given as $ V_{DC}$ (Velocity of D with respect to A) is 20 m per second towards north, $ V_{BC}$ is 20 m per second ...
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0answers
24 views

Relative motion question on flag fluttering

Question: a flag in a bus is fluttering in the north direction and wind is blowing the east direction.ther what is direction in which bus is moving? My take:I think that if there would have been no ...
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1answer
3k views

Finding the point of collision between two objects when acceleration is constant

$\newcommand{\accunit}{\mathrm{m}/\mathrm{s}^2}$ A coin is dropped 60.0m above the top of an elevator car. The coin is dropped just as the car begins to move upwards. The elevator first ...
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1answer
50 views

Explain how $\Delta v_{\perp}=v\Delta\theta$

In The Feynman lectures, under the chapter entitled Vectors, Feynman writes: My two intimately related questions are: 1) What does he mean by the magnitude of velocity? is he talking about the ...
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3answers
162 views

Animating an Acceleration Vector - Acceleration of object on a crested path in gravitational field

So I was reading in Chapter 3 of my textbook, Sears & Zemanksky's University Physics with Modern Physics by Young and Freedman, 13th Edition, and the discussion took us to a definition of the ...
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3answers
2k views

Inertia Vs Momentum

At my recent lesson on kinematics, my teacher taught about inertia and momentum. This is what she said. Inertia: a characteristic of an object that resists changes to its state of motion. Momentum: ...
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4answers
134 views

Calculating how fast a mass needs to travel in order to launch itself from a hill

Today I was driving on a hill side and on the opposite lane this very careless gentleman was traveling at a very high speed on a large truck that I surely thought his truck would of lifted off the ...
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2answers
41 views

What is special about the 45 degree point for projectiles?

This is a question from a book for which I HAVE the solution to BUT I don't understand the concept. Briefly: "a mass is projected horizontally from a cliff with velocity V. 3 seconds later the ...
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1answer
57 views

Change of direction in physics when an object in motion stops

Consider an object moving with an acceleration $a = -1 \text{m/s}^2$ starting with speed $v(0) = 4 \text{m/s}$ towards east and stopped after 4 seconds. (There are no friction.) After 4 seconds, the ...
0
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1answer
61 views

Why would the norm of these vectors be 1?

Let a Cartesian coordinate system $uOx$ coincides with a vertical plane so that $Ou$ is the horizontal axis and $Ox$ is the axis oriented vertically upwards (see Fig. 1). We are looking for the ...
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7answers
8k views

I need help with finding distance traveled

How do I find the distance traveled of an object if the speed is not constant?
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1answer
39 views

How to know if a body is travelling with uniform acceleration or not?

One of the Example in my Textbook is A body travels a distance of 2 m in 2 seconds and 2.2 m in next 4 seconds. What will be the velocity of the body at the end of 7th second from the start. In ...
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4answers
60 views

Can we observe two different events occuring at the same point?

I was wondering a situation. Suppose a train is moving with a certain acceleration. It turns on its front light at a certain time, and it's back light say t s after. But to a inertial, or non ...
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1answer
69 views

Are perpendicular components special in vectors?

We can split a vector (velocity/displacement vector) along any two directions as long as the resultant of the oblique components of the vector is same as my original vector. Similarly if we have to ...
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3answers
1k views

Radius of curvature

I have come across a question that asked me to find the radius of curvature of a projectile. As far as I know, the path of a projectile is a parabola and I have found mention of the radius of ...
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1answer
33 views

Is motion along the $x$ and $y$ axises independent with quadratic drag?

It's often stated that motion in the $x$ and $y$ axises are independent, so that changing the $x$-velocity will not influence changes in the $y$-velocity. To me it seems that with quadratic drag (drag ...
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5answers
5k views

Force applied to wheel in pure rolling motion at contact point with road [closed]

Suppose a wheel with radius $R$ is resting on a non-inclined surface. A torque $\tau$ is applied to the wheel center. In an attempt to prevent wheel from spinning, the ground applies a static friction ...
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3answers
42 views

Displacement based on acceleration in km/h$^2$

For calculation of displacement based on acceleration and time, I have the formula below: $$ x = v_0t + \tfrac{1}{2}at^2 .$$ If I get $a$ in km/h$^2$, and $x$ in km and $v_0$ in km/h and I suppose ...