What is Kinematic: Definition and 405 Discussions

Kinematics is a subfield of physics, developed in classical mechanics, that describes the motion of points, bodies (objects), and systems of bodies (groups of objects) without considering the forces that cause them to move. Kinematics, as a field of study, is often referred to as the "geometry of motion" and is occasionally seen as a branch of mathematics. A kinematics problem begins by describing the geometry of the system and declaring the initial conditions of any known values of position, velocity and/or acceleration of points within the system. Then, using arguments from geometry, the position, velocity and acceleration of any unknown parts of the system can be determined. The study of how forces act on bodies falls within kinetics, not kinematics. For further details, see analytical dynamics.
Kinematics is used in astrophysics to describe the motion of celestial bodies and collections of such bodies. In mechanical engineering, robotics, and biomechanics kinematics is used to describe the motion of systems composed of joined parts (multi-link systems) such as an engine, a robotic arm or the human skeleton.
Geometric transformations, also called rigid transformations, are used to describe the movement of components in a mechanical system, simplifying the derivation of the equations of motion. They are also central to dynamic analysis.
Kinematic analysis is the process of measuring the kinematic quantities used to describe motion. In engineering, for instance, kinematic analysis may be used to find the range of movement for a given mechanism and working in reverse, using kinematic synthesis to design a mechanism for a desired range of motion. In addition, kinematics applies algebraic geometry to the study of the mechanical advantage of a mechanical system or mechanism.

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  1. A

    I Why are the accelerations not equal?

    ##\vec n_2## points to the diagonal top left. The velocity v is a function of t. So for example ##2t^2## and a = dv/dt. Putting the velocity vector into ##\vec n_1## and ##\vec n_2## terms. $$\vec v = v sin\theta \vec n_1 + v cos\theta \vec n_2$$ $$\vec v = -v \vec i$$ $$\vec a = \frac{d\vec...
  2. Ineedhelpwithphysics

    Free fall kinematics problem

    I am super stumped at this question, the answer key is telling me 6.78 downwards, i think I'm reading and observing the question wrong. Isn't final velocity 0 so why can't i do 0 = v0 -9.8(0.25) -2.45 = v0 But when I use the second the equation -2 (displacement of door) = v0(0.25) + 1/2...
  3. S

    Kinematic car overtake problem: Don’t know what to do...

    This is what I've done so far: 54 km/h = m/s 72 km/h = m/s a = 2,0 m/s^2 A = d_1 = v * t = 15 * 10 = 150 m B = d_2 = v * t = 20 * 10 = 200 m d_3 = d_1 - d_2 = 200 - 150 = 50 m Don‘t know how to continue to solve the problem.
  4. imbumb

    B Jaan Kalda kinematics -- Radius of Curvature of a Cycloid

    Cycloid is a curve which can be defined as a trajectory of a point marked on the rim of a rolling wheel or radius R. Determine the curvature radius of such curve at its highest point. what you need to do is to equate 4v²/r with v²/R and to get that r=4R but i dont understand why the answer...
  5. M

    Engineering Kinematic modelling of a mechanism (General Crank)

    Hi, I was wondering if you could help me with a job at the university that consists of the kinematic modeling of mechanism number 3 in the image attached to this message. I have to set up the constraint equations and then solve the position, velocity and acceleration problem. For now I would...
  6. C

    Solving kinematic formula for t

    For ## d = v_it + 0.5at^2##, can we solve for t without using the quadratic formula? Many thanks!
  7. N

    Number of collisions by a bullet

    How to find the collision number if the moving bullet hits a few wooden blocks and every collision takes 10 percent of its speed. In which block will the bullet stay?
  8. A

    I Deriving kinematic equation for position

    We usually have an initial time and then find an equation for the variable final time. Can we derive a formula to calculate position with final time and variable initial time. ##v = v_i + a(t_f - t_i)## ##dx = v_idt + at_fdt - atdt## integrating ##x_f - x_i = v_i(t_f - t_i) + at_f(t_f - t) -...
  9. dorothy

    Solution Attached: Download Now!

    The attached pdf is my solution. Thank you!
  10. H

    Kinematic Problem w/ Parabola: Solving w/ KE Theorem?

    This is not really a homework problem (it could be made to be though). I kind of made it up, inspired by a youtube math challenge problem involving parabolas, a water fountain where A = 1, R = 3, and H = 3. The solution given (h = 9/4) was based off simple math utilizing vertex form of a...
  11. Mjusttheletter

    100m dash kinematics problem

    So what I have done is that on question 7 I know he is accelerating to constant my knowns are that it is from initial and acceleration is given so I have that for my first phase the second phase is that Your vfinal is your new initial for it and acceleration is the constant but you don't know...
  12. runningphysics

    Solving Motion Equations with Integration

    I'm not sure where to start, when I tired using integration of the initial equation to get pos(t)=-.65t^2 i + .13t^2 j + 14ti +13tj but after separating each component, i and j, and setting j equal to zero I got 0 or -100 seconds which doesn't seem like a reasonable answer.
  13. GiantYoda

    Kinematic Equations in Projectile Motion (this approach is not working)

    Givens: Vyi=12.5 m/s Vyf=-12.5 m/s (at the same horizontal level) ay=-9.81 m/s^2 Δy= zero m (as the displacement on the y-axis, when the projectile reaches the same horizontal level, is zero m) Δt=? When I use Δy=[(vyi+vyf)/2]*Δt I get the time as undefined. Δt= 2Δy/(vyi+vyf) = 2*0 m/(12.5...
  14. PeterDonis

    I Kinematic Decomposition for "Rod and Hole" Relativity Paradox

    In a recent thread, I said that if there was interest, I would post in a separate thread the calculations for the kinematic decomposition of the congruence of worldlines describing the rod in the "rod and hole" relativity paradox discussed in that thread. Since there was interest, I am posting...
  15. Nick tringali

    Angular kinematic problem -- An accelerating merry-go-round

  16. ayans2495

    Kinematics and One Dimensional Motion

    Would we assume that the deceleration of both instance are the same?
  17. mncyapntsi

    1-D Motion, calculating final velocity

    Hello! I have done this problem : vf^2 = (4.0x10^5)^2 + 2(6.0x10^12)(5x10^-3) so vf= sqrt((4.0x10^5)^2 + 2(6.0x10^12)(5x10^-3)) I get vf = 4.7 x 10^5 m/s However, the textbook solutions says vf = 8.7x10^5 m/s. Where did I go wrong? Thank you for any help! :)
  18. bluesteels

    I How to know whether it is +,- g and +,- y in the kinematic equations?

    i was doing some problem and i have a hard time figuring out when will the y be positive and negative and same with the gravity idk if it -9.8 or 9.8
  19. mncyapntsi

    Is Negative Acceleration Always Indicative of Slowing Down?

    I've written in that only the first statement was False, however my classmates aren't getting the same answer? Please help clarify...
  20. R

    Show that a projectile lands at a distance ##R = \frac{2v_0^2 sin \theta cos(\theta + \phi)}{g cos^2 \phi}##

    ##V_x = V_0 cos \theta ## ##x = V_0 cos \theta t## ##V_y = V_0 cos \theta ## ##y = V_0 cos \theta t## ##F_x = m\ddot{x}## ##-mgsin \phi = m\ddot{x}## ##\dot{x} = -gtsin\phi + V_x## ##x = -\frac{1}{2} gt^2 sin \phi + V_x t## ##x = -\frac{1}{2} gt^2 sin \phi + v_0 cos\theta t## ##F_y =...
  21. P

    Kinematic diagram of a gear mechanism

    Can anyone help me with a kinematic analysis for the mechanism attached below? I need the outline of the mechanism, its notes and the necessary formulas to find out the transmission ratio and the rest of the values.
  22. E

    When do I use this k5 Kinematic Equation

    Vƒ = velocity final Vi = velocity initial a=acceleration t=time 0.5 = ½ ^2 = squared - = minus d = displacement Equation d = Vƒt - 0.5at^2
  23. S

    Equations for a mass falling to Earth from a distance

    I have a question : If we consider the change in g due to distance from the Earth core; then y=distance from earth’s core t=time G=gravitation constant M=Earth’s mass k=GM $$y^2(t)=\frac{k}{y(t)^2}$$ If we consider air resistive force as proportional to speed squared, then: m=falling object...
  24. greg_rack

    Check on a basic kinematic problem (FBD of a cabin on a Ferris wheel)

    Hi guys, given the "blacker" to be the cabin under consideration, I firstly wrote its weight force; then, my confusion started when drawing the force applied on the cabin by the structure(##F_{r}##). I concluded it must have been both counter-acting the weight, and acting as a centripetal...
  25. Lucho G

    Are there kinematic equations that are not always true?

    please I need to clarify this question thanks sincerely Luis
  26. L

    Calculus and Kinematic equations--- seeing the logic

    Details of Question: ds/dt= v which becomes ds=v dt, where s=displacement, t =time, and v=velocity Then we can integrate both sides of this equation, and do a little algebra, and turn the above equation into: s − s0 = v0t + ½at2 My main question is about the integration of...
  27. wcjy

    Electric field problem using Gauss' law: Point charge moving near a line charge

    F = qE ma = (2*10^-6) * (λ / (2pi*r*ε0) ) ma = (2*10^-6) * (4*10^-6 / (2pi*4*ε0) ) => I am not certain what to put for r ( But I sub in 4 because dist is 4) a = ( (2*10^-6) * (4*10^-6 / (2pi*4*ε0) ) )/ 0.1 a = 0.35950 v^2 = U^2 + 2 a s v = 0 u^2 = -2 a s => Can't sqrt negative so...
  28. burian

    Application of momentum conservation in inelastic collisions

    So, what I did was suppose the mass of ramp is $ M_r$ and let velocity at B of block be v, then, after inellastic collsion both bodies v' velocity at B , $$M\vec{v}= M_r \vec{v'}+ M \vec{v'}$$ or, $$ \frac{M}{M +M_r} \vec{v}= \vec{v'}$$ Now, Suppose I take the limit as mass of ramp goes to...
  29. Tymofei

    Calculating the Moment from a Different Vantage Point

    Summary:: Just a simple 3d rigid dynamics question which I am trying to solve by placing coordinat system differently from original solution.Everything looks ok but results are different. Mod note: Post moved from technical section. Thats my question.As you see coordinate system was located...
  30. V

    Finding the y-component of a velocity vector

    The first thing I did, was to find the equations for player A (p) and ball's (b) path (for each i and j component I used the equation I wrote in the relevant equations) and then I found the derivative of both equations so I could have the velocity: $$\vec{r}_p(t)=(6t^2+3t)\hat{i}+20\hat{j}...
  31. IamVector

    Hard kinematics problem: Block pushed onto a moving conveyor belt

    stuck on this question
  32. E

    Maximum Distance a Projectile Moves Up an Inclined Plane

    the red line is the initial velocity, the grey parabola is the path of the projectile. hi there...I'm kinda stuck at the part b of this problem. I can do part a with no problem. can anybody explain to me how to do the differentiation needed to solve part b?? by explain I mean explain the...
  33. S

    Engineering Kinematic and geometric similarity (fluids)

    My attempt at a solution is to start off first denoting V_a to be the automobile an V_e to be the economy version. Same goes with l_a and l_e. To try and relate the two I have tried: V_a I_a = V_l L_e, however I am really not sure how they got the square root. The answer is: v = V sqrt(l/L)...
  34. M

    Kinematics Problem: constant acceleration, motion in a line

    I've been attempting to solve this problem for three days now. I have thrown away my old attempts (like, scrumpled up into the bin), but my old attempts involved: Trying to set up simultaeneous equations relating the journeys between EH and FG to find the deceleration, but the reason why this...
  35. radhxy

    Issac Physics 'Three Collisions' High School Homework - Kinematic

    Homework Statement: Three particles A, B, and C, each of mass 𝑚, lie at rest in that order in a straight line on a smooth horizontal table. The particle A is then projected directly towards B with speed 𝑢. The masses of A, B, and C are now 𝑚, 2𝑚 and 3𝑚 respectively: Again find the fraction of...
  36. Delta_Craig

    Kinematic in Quadratic Form Equation (missing something simple)

    I just ran this pretty quick at work. But this is the general outline. Sorry for the slop, it will get better with time. Thanks in advance and any additional info can be supplied. The material is from the Khan free course. ..... A student is fed up with doing her kinematic formula homework...
  37. S

    Kinematic Equations: Find the time t when two objects meet

    Part A) So, I set the two positions equations of A and B equal to each other since the position has to be the same. A: 0 + 0 + 1/2(2)t^2 = 50 + 0 + 1/2(4)t^2 :B I know I have to solve for time t, but there's no way to solve it with both sides having t^2 so I am not sure which variables I got...
  38. Like Tony Stark

    Doubts on the sign of acceleration

    What should I do? Because I have two possibilities. I have ##0=5+at## so ##-5/t =a##. But then I can also say that the acceleration is a negative because it is stopping, so I can write it like ##0=5-kt## and then ##5/t =k##
  39. J

    Kinematics of a kicked football

  40. Like Tony Stark

    Relative rotational motion on a disc

    The first doubt that comes to my mind is "I have to determine the acceleration with respect to what?", because the problem doesn't tell. Then, I have some problems when having to plug the data in the formula of acceleration. ##\vec a_B=0## because the origin isn't accelerated, ##\vec{\dot...
  41. Santilopez10

    Kinematics question on 2 planes moving relatively with each other

    So my problem isn't actually finding the components, but knowing if the initial approach I took is correct. So what I did was: At first I found that at the same instant, ##x_{B/A}=10500 m## so then I wrote the equation of motion for plane B respect to A: so $$\vec a_{B/O}- \vec a_{A/O}=\vec...
  42. Santilopez10

    Finding the Acceleration of a Bag Being Raised by a Rope on a Moving Kid

    So what I did was at first consider the case the kid is below the branch, so that x=0,t=0, then I thought that the length L of the rope should be ##L=2h## because we know the radius from the branch to the kid is just ##x^2+y^2=r^2## and when x=0, y=h. So then I wrote the motion equations for the...
  43. Santilopez10

    Intrinsic coordinates kinematics problem

    So I know that ##a_t = \frac{dv}{dt}=-ks## and ##\frac{dv}{dt}=v\frac{dv}{ds}## then: $$v dv=-ks ds \rightarrow (v(s))^2=-ks^2+c$$ and using my initial conditions it follows that: $$(3.6)^2=c \approx 13$$ and $$(1.8)^2=13-5.4k \rightarrow k=1.8 \rightarrow (v(s))^2=13-1.8s$$ What bothers me is...
  44. Santilopez10

    Plane being tracked by radar

    I tried to workout the problem but I find motion in different coordinates systems a bit weird at the moment, so only thing I could do is realize that the x component of ##\vec r(t)## is: $$vt +x_0$$ but for simplicity we will use the initial condition ##x_0=0## so that ##t_0## is the moment the...
  45. J

    Equation of motion of a mass on a 2d curve

    So ##T+U=\frac{1}{2}m(\dot{x}^{2}+\dot{y}^{2})-mgy=constant##. If I derive this with respect to ##t## $$\dot{x}\ddot{x}+\dot{y}\ddot{y}-g\dot{y}=0$$ Then I use ##\dot{y}=\dot{x}\frac{dy}{dx},\ddot{y}=\ddot{x}\frac{dy}{dx}+\dot{x}^{2}\frac{d^{2}y}{dx^{2}}## to get...
  46. E

    Airtime for halfpipe skateboarder

    I've calculated the potential energy at the top of the halfpipe, before the boarder drops in: PE = 39.5 kg * 9.8 m/s^2 * 3.66 m = 1416 J Since the boarder would have no potential energy and all kinetic energy at the bottom of the halfpipe, KE = 1/2mv^2 = 1416 J 1/2 (39.5 kg) (v^2) = 1416 J So...
  47. msfd

    Question regarding this Basketball Kinematics Diagram

  48. V

    Man on ladder: jump off instantly vs last moment?

    So there are two cases: a). free fall (straight forward for me) b). ladder rotating and jumping off in last moment (I am interested in trying to understand this case) I believe I should take into account momentum at the time the man hits the ground in both cases? The smaller, the better. Or...
  49. V

    How can I calculate the acceleration of a baseball thrown by a pitcher?

    Hello. I have just started studying physics. Can someone explain to me how can I type in formulas here using Tex for nicer formatting? I suppose the force is F = ma. Question is: what is a? The starting throw angle is not mentioned, I suppose this task has to be related to gravity. All I know...
  50. Emilyyyyyyyyy

    Calculate the impact force when falling from a height

    To find vx vx = dx/t = 3.86 m/1.5 s= 2.573 m/s To find Ek Ek = ½mvx²= ½(79.4)(2.573)²= 262.8 J W = FnetΔd Fnet = 262.8 J/ 3.86 m = 68 N He hits him with a force of 68N
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