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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2
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0answers
22 views

Position, velocity, acceleration, jolt, and [duplicate]

I am familiar with the fact that $\displaystyle{\frac{dx}{dt}}=v$, $\displaystyle{\frac{dv}{dt} =a}$, and $\displaystyle{\frac{da}{dt}=J}$ where $J$ denotes the 'jolt', or jerk. Are further ...
127
votes
17answers
33k 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 ...
5
votes
2answers
487 views

How is Chasles' Theorem, that any rigid displacement can be produced by translating along a line and then rotating about the same line, true?

Chasles' Theorem in its strong form says: The most general rigid body displacement can be produced by a translation along a line (called its screw axis) followed (or preceded) by a rotation about ...
0
votes
1answer
39 views

Momentum equation of a beam hitting a stationary target to create antiprotons

I'm struggling with the solution of a physics exercise which is to calculate the minimum energy needed to create antiprotons when a proton beam scatters on a stationary proton target: $$p + p \...
1
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0answers
57 views

Does a photon follow a straight trajectory in a thin transparent film? [closed]

Emulsion films (developed by F.Powell) /by example/ show that elementary particles follow a straight trajectory staying in a film. The reason was clarified by Francis Mott in his famous 1929 paper ...
0
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1answer
53 views

How do they know their velocity in a spaceship? [closed]

Suppose a spaceship is going to Mars or to Jupiter, they switch on their thrusters and accelerate for a certain period, how to they know their position / velocity, do they refer to the Sun?
0
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2answers
43 views

Momentum of a rack and pinion gear system excited by a time variant force

Background I have a rack and pinion gear system as shown in the image below The pinion gear is attached to a flywheel at the back. The first state of the system, none of the gears or the ...
-2
votes
3answers
553 views

Projectile Motion

I know the angle at which a projectile is launched, how far it needs to go, and also the maximum height. How can I find the initial velocity needed (disregarding air resistance)? Currently, I am ...
1
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0answers
62 views

How do I model the motion of a particle changing acceleration vector (2D)?

I want to model a particle with an arbitrary initial velocity, and estimate the time it takes to reach a final point given a constant magnitude of acceleration. It should take the quickest path to the ...
0
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3answers
93 views

Rolling dynamics of round objects down an incline

If a cylinder is rolling down an inclined plane with inclination $\theta=30^\circ$ (with coefficient of static friction between cylinder and the plane $\mu_s=0.8$) without slipping and it has mass $...
0
votes
1answer
48 views

The elevator and the bolt [closed]

I had this question, I don't seem to get what I am doing wrong so here it goes:An elevator car whose floor to ceiling distance is equal to $2.7 m $ starts ascending with a constant acceleration of $1....
0
votes
1answer
87 views

What is the best way to calculate impact time with collisions?

I've been teaching myself physics and I've been wondering about the impact time in collision calculations. The scenario I've been using to learn is an object with a mass of 4000 kilograms colliding ...
0
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4answers
1k views

How is acceleration measured if there is change only in the direction of velocity & not magnitude?

The formal definition of acceleration is It is the measure of how fast the velocity changes with respect to time. Now, when the magnitude of velocity changes, acceleration $$\vec{a} = \frac{d \...
1
vote
0answers
82 views

Inverted pendulum with reaction wheel

I'm a little confused about the equations of motion of the reaction wheel pendulum. It is used in self balancing bicycles - see vide link in comments (I can't add another link here due to low rep). Or ...
1
vote
2answers
89 views

non constant acceleration problem [closed]

The acceleration of an arrow from a bow falls from $6000m/s^2$ to zero when it leaves the bow after travelling a distance $x=0.75m$. Assuming that this acceleration can be expressed by the linear ...
2
votes
2answers
40 views

Water flow in salt solutions contemporary exposed to an electrical and constant magnetic field

When a permanent magnet is held motionless close to a salt solution which already has been exposed to an electrical field a flow in the water will be induced and can be detected by applying some ...
0
votes
1answer
9k views

Average Resistive force exerted by a wooden block on a bullet [closed]

A bullet of mass 0.04 kg moving with a speed of 90 m/s enters a wooden block and is stopped after a distance of 60cm. What is the average resistive force exerted by the block on the bullet? Ok, so ...
2
votes
2answers
408 views

Stanford: “Objects in spacetime all move at constant speed $c$.” Are they right? [duplicate]

In this Stanford University lecture on Relativity, it is stated: Likewise, objects in spacetime all move at constant speed c in spacetime but if you change its direction, say by moving at speed v in ...
1
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2answers
60 views

May a point rotate about itself?

Suppose we have two equivalent rigid cylinders. Cylinder 1 is moving (translating) with constant velocity of v. Cylinder 2 is rotating without slipping and its center’s velocity is constant and equal ...
0
votes
0answers
32 views

Formula of distance traveled in Nth second by a uniformly accelerated body is dimensionally incorrect [duplicate]

$S_N = v_0 + \frac{1}{2}a(2N+1)$ This is the expression for the distance covered in the $N$th second of the journey, by a uniformly accelerated ($a$) body starting with initial velocity $v_0$. This ...
1
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2answers
939 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 $s_t= u+\frac{a}{2}(2t-1)$ ...
0
votes
3answers
49 views

How to calculate projectile path having starting and end point?

I want to show a projectile path between two points (x1,y1) (x2,y2 ) on graph. Here I know two points, start point and end point. I tried solving by taking launch angle as 45 degree, it doesn't seem ...
-1
votes
1answer
29 views

How does the relationship between velocity and net force affect the direction of a moving object?

I already know that for a moving object with velocity $\ v_i$,and has a net force, $\ F_{net}$, the trajectory of the object will start with the direction of $\ v_i$ and gradually deflect to the ...
1
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0answers
57 views

Determining the forces required to maintain a static center of mass position; one with velocity and one with acceleration [closed]

I'm having a bit of trouble wrapping my head around this conceptually. The magnitudes and directions of the forces on two of the particles are indicated. What are the magnitude and direction of the ...
9
votes
4answers
864 views

Where does movement come from? [closed]

When you put a body in motion, where does that movement come from? Ok, you will say things like "acceleration", but where does that acceleration come from? Then you might say "a force is creating the ...
2
votes
2answers
230 views

What is the position as a function of time for a mass falling down a cycloid curve?

In the brachistochrone problem and in the tautochrone problem it is easy to see that a cycloid is the curve that satisfies both problems. If we consider $x$ the horizontal axis and $y$ the vertical ...
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votes
1answer
25 views

How to express in terms of spacetime intervals the average speed of one participant having moved between two suitable others

Given a flat region of spacetime as set $\mathcal S$ of events together with values of spacetime intervals (up to a common non-zero constant) for each pair of events, $s^2 : \mathcal S \times \mathcal ...
-7
votes
1answer
78 views

If a being was able to swallow itself, where would it go physically? [closed]

if a being was made from a special type of material that allowed it to stretch and was very flexible, if it were to swallow itself, where wold it go. I mean the physical aspects of it since it wont be ...
1
vote
1answer
2k views

A ball is thrown up, and a second ball is dropped- what is the maximum initial velocity of the first ball so that [closed]

This question only exists in one dimension, the y axis. A ball is thrown upwards with an initial velocity $V_o$ from a roof with height $h$. One second later, a second ball is dropped from the same ...
2
votes
2answers
42 views

Relationship between velocity and position due to constant jerk proof check [closed]

In constant accelaration and linear (1D) motion, we can show that relationship between velocity and position is quadratic (parabola) by We can write $v$ in the form of $v=v(x(t))$ \begin{equation} a=\...
0
votes
1answer
77 views

Angle required to hit the target in projectile motion

Consider the problem of projectile motion where the angle to hit a target $(x,y)$ is asked, once given the initial velocity magnitude $v_0$. The projectile is fired from the point $(0,0)$. Here is ...
2
votes
2answers
596 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 ...
0
votes
1answer
38 views

Acceleration of moving reference frame

I want to simulate the readings of an accelerometer that is arbitrarily moved through 3D space. In an inertial reference frame $W$, the motion of the accelerometer is described by it's linear ...
2
votes
2answers
4k views

Is squared motor gearbox ratio proportional to inertia ratio?

I read an interesting article http://m.machinedesign.com/news/motor-sizing-made-easy It is very interesting, but I can not follow the 2nd last paragraph. I don't understand why it is true. ...
-3
votes
1answer
41 views

How do you know when to use kinematic equations as apposed to $v = d/t$ and $a = v/t$? [closed]

How do I know when to use v = d/t and a = v/t or d=vi+​1/2​​at^2 and vf = vi + at?​
0
votes
2answers
67 views

How to determine the net velocity change applied by a force vector [closed]

I am a little stumped by the answer of this question. The question reads, "In three situations, a single force acts on a moving particle. Here are the velocities (at that instant) and the forces: ...
2
votes
1answer
99 views

Why can't I use conservation of energy to find ratio of final velocities on different planets?

The question is An object of mass $m$ is allowed to slide down a frictionless ramp of angle $\theta$, and its speed at the bottom is recorded as v. If this same process was followed on a planet ...
0
votes
0answers
32 views

Helicity of massive particle at high enengy

We know that massless spin-1 particle like photon only has two helicity state (-1,1), what about the helicity of massive spin-1 particle (W boson) at very high energy? Does it have helicity 0 state ...
0
votes
2answers
283 views

Why do objects seem to move faster (relatively) when they move tangential to the observer?

I've observed this loads of times while travelling, in cars, trains,etc.I can't quite put it in words and therefore I've roughly made a diagram to assist my question. Assume an observer is travelling ...
8
votes
3answers
539 views

What is the kinematics of a particle with complex mass?

particles with real-mass have time-like kinematics ($ds^2 > 0$). particles with zero-mass have light-like kinematics ($ds^2 = 0$). particles with imaginary-mass have space-like kinematics ($ds^2 &...
1
vote
1answer
120 views

Are velocity and acceleration smooth quantities?

My thinking: acceleration corresponds to a force which is instantaneous, so the acceleration of a rigid body can be rather spiky (non-smooth) velocity (angular velocity) describes the ratio of ...
2
votes
2answers
58 views

Does the position-time graph have to be a smooth function?

If at some time $t$ there were a discontinuity in the velocity-time graph, then the acceleration would be infinite at $t$. So intuitively, it seems that the velocity-time graph must be continuous. I ...
0
votes
1answer
67 views

Olympiad problem - struggling with polar coordinates [closed]

This is a physics olympiad problem; and I am still struggling with it. I will quote it here: " A particle moves along a horizontal track following the trajectory $r=r_{0}e^{-k\theta}$, where $\theta$ ...
-1
votes
1answer
52 views

Uncertainty in Range of Projectile [closed]

If we are given that a projectile is launched with velocity 10m/s at an angle of $45^\circ$ and uncertainty in angle is of $0.5^\circ$ . What is the uncertainty in the range of projectile. The problem ...
1
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0answers
21 views

Kinetic energy vs Kinetic Energy scenario in a collision, mechanical energy used for work?

Most collisions have Kinetic energy conserved or in the case of inelastic collisions energy is lost into other forms. Though the equation of "TMEi + Wnc =TMEf" is true however, what if two unequal ...
1
vote
2answers
52 views

Why do I get two different answers? Using Calculus and Using Newton for Distance/Velocity [closed]

Why do I get two different answers? QUESTION: How long does it take to slow down from 8000 m/s to 6000 m/s with an acceleration of -400 m/s^2 ? GIVENS D distance V velocity T time V initial ...
1
vote
3answers
54 views

Why the similarity in the Equations of Motion for Rotational and Rectilinear Motion?

These are the equations of motion given constant acceleration, for first rectilinear and then rotational motion. Rectilinear Motion: Rotational Motion: While the variables have changed, and the ...
1
vote
1answer
51 views

Homework: Expression for minimum speed to cause collision of objects / simple kinematics

I have a question which is worded as follows: Person A throws a rock at a 45∘ angle to the horizontal, aiming at Person B who's standing on a building at heigh h above level ground. At the ...
2
votes
2answers
133 views

Explicit Function for Bouncing Ball [closed]

I was wondering if it's possible (and if so, how would you go about it) to write an explicit function for the position of a ball bouncing as a function of time (assuming a coefficient of restitution 0 ...
0
votes
0answers
51 views

What kind of unit is $m^2s^{-4}$ in terms of gyro/accel?

Background While working on something in the field of avionics, I have discovered the following unit as part of an inertial-physics equation... $$m^2s^{-4}$$ I am trying to figure out the formal ...