What is Kinematics: Definition and 1000 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

    Stuck on a rotational kinematics question

    Homework Statement A barrel is lowered into a boat using the illustrated apparatus. The barrel can be considered to be a uniform cylinder with M=100kg and r=0.40m. The weight on the other end of the rope has m=30kg. Assume that the barrel does not slip against the wall, that the other 2...
  2. T

    Basic calculus question (kinematics)

    Could someone point me to the proof or reasoning behind the steps: 1) a = dv/dt 2) a dt = dv 3) ∫a dt = ∫dv I know this works, but I'm missing understanding in the math behind it, and I'm not sure what to type into google. Thank you very much
  3. M

    Rotational Kinematics (String attached to disk)

    Homework Statement Determine the relationship between the angular acceleration of the flywheel, the downward acceleration of the block, and the radius of the ring. Known data: Mass Ring: 1.420 kg Radius Ring (Inside, then Outside): 5.10 cm, 6.325 cm Mass Disk: 1.455 kg Radius Disk...
  4. B

    Kinematics of Euler Bernoulli and Timoshenko Beam Elements

    Folks, Trying to get some appreciation for what is going on in the attached schematic of 1)Euler bernoulli and 2) Timoshenko beam elements. For the first one, ie the top picture, how was ##u- z \frac{dw}{dx}## arrived at? thanks
  5. A

    Questioning a Linear & Angular Kinematics Equation

    Homework Statement I'm reviewing a chapter relating linear and angular kinematics, and I came across this equation.. why does it work and where does it come from? I can't seem to find anything in the textbook explaining it. Homework Equations a = sqrt( (tangential acceleration)2 +...
  6. M

    Difficult 2D Kinematics Question

    Homework Statement A basketball is thrown from a height of 2m. The direction of its velocity when it hits the rim of the basketball hoop is 45 degrees below the horizontal. The basketball hoop is 3m above the ground and 4.5 m in front of the shooter. How long does the ball take to hit the rim...
  7. K

    What is the effect of acceleration on a projectile's motion?

    The equation v22 = vo2 + 2aΔy is used to determine the change in position, acceleration, or velocity of a particle under the influence of a quadratic force. on earth, the acceleration value in this equation would, under normal circumstances, be a= -9.8 m/s2. so, this...
  8. P

    Dynamics And Kinematics Problem

    Homework Statement Given: m = 17kg Vi = 0 Fa=42N θ=25 Mu=0.15 T=125s Diagram: http://s14.postimage.org/euy3whikh/New_Bitmap_Image.png Find: Δd a block accellerates from rest for 125s find the displacement. Frictional forces act on the block. A force applied is 25 degrees above the...
  9. H

    Basic motion question involoving kinematics

    Hey everyone, I have a question from a past exam paper that I was doing. I spent a lot of time trying to solve it, however I have failed. I would appreiciate it if I got some assistance from a professional or someone that can answer it correctly. Question: A car is parked on the side...
  10. Darth Frodo

    Did I Solve the Object Thrown Vertically Upwards Problem Correctly?

    Homework Statement 5. An object is thrown vertically upwards with a speed of 72 kilometres per hour. How long does it take to reach a point 25 meters below the starting point? You can take g as 10 ms-2 for convenience. Here is my answer. I got 4 yet the answer is 5...
  11. M

    Solving Angular Kinematics: Swing Bridge Turned in 120 secs

    A swing bridge has to be turned through a right angle in 120 seconds. The first 50.4 seconds is a period of uniform angular acceleration ; the subsequent 34.8 seconds is a period of uniform angular velocity and the third period of 34.8 seconds is a period of uniform angular retardation. Input...
  12. T

    Path following control robot kinematics and dynamics

    Hello, I have a general question regarding what is the best controller (PI, PD, etc.) to control the position of a mobile robot in order to follow a known path. The mobile robot at hand is a mechanism (a 4 bar linkage with its two base gliding on two parallel but not straight rails) and I...
  13. H

    How Do You Calculate Hang Time and Velocity in Cat Jump Kinematics?

    Homework Statement In a 1985 study, cats were trained to jump up and touch a cotton ball in an effort to study their thigh muscles. One cat was able to jump 2.93 meters off the ground. What is its hang time? In other words, what total time was the cat in the air? s What was its...
  14. P

    Kinematics (Projectile Motion)

    What happens to range if the initial height is doubled. Say if something is shot at 2 ft and then its shot at 4 ft high, what happens to range? I know that its conservation of energy. I just have no idea how to come up with the right answer
  15. P

    What is the relationship between range and initial height in projectile motion?

    Range and Height Kinematics? What happens to range if the initial height is doubled. Say if something is shot at 2 ft and then its shot at 4 ft high, what happens to range?
  16. M

    How Long Does It Take for a Flywheel to Reach 125 Rev/Min from Rest?

    A flywheel 1.2 m in diameter is uniformly accelerated from rest and revolves completely 68 times in reaching a speed of 125 rev/min. Find the time taken to reach this speed i have been given the correct answer as 65.29 seconds Wht i have up to now ω1 = 0 ω2 = 125 r/min = 125/60 =...
  17. L

    The Equations of Rotational Kinematics help

    [b]1. Consider a fan that has rotated by a total of 2 complete revolutions from where it started. This quantity (2 revolutions) is analogous to what quantity in linear kinematics? Position Displacement Velocity Speed Time Time Homework Equations I am...
  18. Z

    A strange kind of straight line kinematics with uniform acceleration.

    Homework Statement A ball is thrown upward from a building 30 meters tall and misses the edge on its way down, hitting the ground 6 seconds after it was thrown. A) With what speed was it thrown? B) What is its highest height?Homework Equations Vf = Vi + at x = 1/2(Vi + Vf) x = Vi t + 1/2(at^2)...
  19. Z

    I need a lot of help with Kinematics and Dynamics so forces and motion

    I need a lot of help with Kinematics and Dynamics so forces and motion would be what you can call that. I have a teacher that does not teach, I have had her for two years in a row now so if I had some knowledge from grade 11, It would still help me but I learned close to nothing in Grade 11 and...
  20. S

    2d Kinematics Problem Final Velocity

    Homework Statement http://imgur.com/fGYf0 Stuck on #3 Homework Equations V = Vi + a*t Y = (1/2)gt^2 + (ViY * t) + Yi The Attempt at a Solution I have found the vertical and horizontal components and the initial velocity. ViX = 6.2 ViY = 9.922 Vi = 11.7 Yf = 0 Yi = 7 Xi =...
  21. V

    Free-fall kinematics on a plane: Displacement from Window to Ground?

    Homework Statement A ball is thrown vertically upward from a window at 10m/s. It hits the ground 5.0 seconds later. What is the height of the window from the ground? Given Vi = 10 m/s Vf = 0 Δt = 5.0 m/s Δa = -9.8 m/s^2 Find Δd(w-g) = ?Homework Equations Δd = Vi(Δt) + Δa(Δt)^2 And the...
  22. S

    Calculating Minimum Distance for Safe Overtaking in a Kinematics Problem

    Homework Statement Suppose that a woman driving a Mercedes zooms out of a darkened tunnel at 30.3 m/s. She is momentarily blinded by the sunshine. When she recovers, she sees that she is fast overtaking a camper ahead in her lane moving at the slower speed of 13.7 m/s. She hits the brakes as...
  23. W

    How Do You Calculate Missile Impact in Kinematics Problems?

    Homework Statement Maverick in an F-14 is moving at a constant velocity of 509 km/hr. He is chasing a "bogey," also known as a Russian MiG-28 (at least, in the movie they were - there's no such thing as a MiG-28), which is moving with a constant velocity of 592 km/hr in the same direction...
  24. P

    How Long Does It Take a Dropped Object to Hit the Ground from a Rising Balloon?

    Homework Statement A balloon is at a height of 81 m is ascending upward with a velocity of 12 ms1. A body of 2 kg weight is dropped from it. If g = 10 ms2, the body will reach the surface of Earth in what time. Homework Equations The Attempt at a Solution I don't think mass...
  25. W

    Rockets and accleration with kinematics

    How would I go about solving a problem like this? What would the answer be? Homework Statement Rockets A and B are fired straight upward from rest at the same time. Rocket A accelerates at 12.2 m/s2, while rocket B accelerates at 15.9 m/s2. Solve for the moment in time when the rockets are...
  26. S

    Kinematics - getting different answers when using different units

    Homework Statement A jetliner touches down at 270 km/h. The plane then decelerates (i.e., undergoes acceleration directed opposite its velocity) at 4.5 m/s2. What’s the minimum runway length on which this aircraft can land? Homework Equations v2fx = v2ix + 2axΔx The Attempt at a Solution i...
  27. V

    Basic kinematics - calculating time

    A boy in a wagon starts from a rest position and then goes down a straight ramp, gaining speed with uniform acceleration as he travels. In 6.00 s, he is traveling at 4.2 m/s. a) What is his velocity at 10.0 s? a = v2 – v1 / Δt a = 4.2 m/s [down] – 0 / 6.0 s a = 0.70 m/s^2 [down] v2...
  28. M

    2D kinematics - conveyer belt question

    Homework Statement Sand moves without slipping at 6.0m/s down a conveyer belt that is tilted 15°. The sand enters a pipe 3.0m below the end of the conveyer belt. What is the horizontal distance between the conveyer belt and the pipe? Not sure where to start.
  29. D

    How Can I Solve 2D Kinematics Problems Using the Quadratic Formula?

    Homework Statement A projectile is shot from the edge of a vertical cliff 60.0meters above the ocean. It has a speed of 100m/s and is fired at an angle of 35 degrees above horizontal. How far from the foot of the vertical cliff does the projectile land. Homework Equations Yf= Yinitial + ViT...
  30. Saitama

    Convergence Time of Moving Points on an Equilateral Triangle

    Homework Statement Three points are located at the vertices of an equilateral triangle whose sides equals a. They all start moving simultaneously with velocity v constant in modulus, with the first point heading continually for the second, the second for the third, and the third for the first...
  31. J

    AP Physics Kinematics 2 Balls Inclined Track

    Consider two balls on an inclined track with a constant angle. Ball A is released from rest at the top of the track. Ball B is given an initial velocity directed down the track. At the instant that the balls collide, Ball A is going 4 times as fast as Ball B. Ball B is still traveling upward...
  32. P

    Kinematics problem, is it possible to solve with given information?

    Homework Statement A missile is launched from a silo 50m deep. After 20 seconds the engine stops, there is a 10 second period where the rocket is coasting straight up. At the end of this period, the rocket is 8000m above the ground. a) What is initial acceleration of rocket? b) What is...
  33. K

    Kinematics with projectile motion(2 questions)

    1) Jim decides to jump a gorge on his skateboard. The gorge is 50 m wide and jim has constructed a 1 m high ramp iclined at 30 degrees to the horizontal. If air resistance is neglected, calculate what speed Bart must reach if he is to land safely on the other side of the gorge. The answer is...
  34. I

    Quick question about kinematics problem?

    Homework Statement A commuter train can minimize the time t between two stations by accelerating (a1 = 0.1 m/s^2) for a time t1 then undergoing a negative acceleration (a2 = -0.5 m/s^2) by using his brakes for a time t2. Since the stations are only 1 km apart, the train never reaches its...
  35. D

    Vi for Constant Acceleration Kinematics

    So, there's a question that's been bugging me. If a ball is thrown upward to find out the height of a flag by timing when the ball passes the flag how do you find the height given that the ball passes the flag twice. When only time is given. So let's say t=5seconds and t=15 seconds I know...
  36. S

    Solving 2D Kinematics Problem: Distance OP in m

    I have a problem with this question. An arrow is shot horizontally towards point O, which is at a distance of 20.0 m. It hits point P (right below point O) 0.10 s later. What is the distance OP (in metres)? What do i need to find? How would i know the time taken for the arrow to reach o?
  37. A

    Kinematics Problem (Find Speed)

    Homework Statement A daredevil motorcyclist attempts to leap a 48m wide gorge. At the side where the cyclist starts, the ground slopes upward at an angle of 15 degrees. Beyond the far rim, the ground is level and is 5.9m below the near rim. what is the minimum speed necessary for the cyclist to...
  38. B

    Confused kinematics equations & ball motion in the air

    you throw a ball straight up in the air with a speed of 7.25m/s. The moment the ball leaves your hand you start running away at a speed of 2.59m/s. How far are you from the ball the moment it hits the ground. So I've gotten better at these kinematics equations but this one has too many...
  39. B

    Sailboat Direction - Kinematics in Two Directions

    Homework Statement A sailboat is traveling east at 5.1m/s . A sudden gust of wind gives the boat an acceleration = (0.80 m/s2}, 40° north of east). What is the boat's direction 6s later when the gust subsides?Homework Equations Vf = V0 + atThe Attempt at a Solution To solve I simply created X...
  40. S

    What is the final velocity of a tossed rock falling into a hole?

    Homework Statement A rock is tossed straight up with a velocity of When it returns, it falls into a hole deep. What is the rock's velocity as it hits the bottom of the hole? Homework Equations The Attempt at a Solution
  41. M

    What is the acceleration of the blue car once the brakes are applied?

    Homework Statement Two cars start from rest at a red stop light. When the light turns green, both cars accelerate forward. The blue car accelerates uniformly at a rate of 4.2 m/s2 for 3.2 seconds. It then continues at a constant speed for 13.2 seconds, before applying the brakes such that the...
  42. A

    How Do You Solve Basic Kinematics Problems in Physics?

    1. Problems: A ball is launched vertically upward and returns to ground level 8 seconds later. Let upward be the positive direction. To what maximum height does the ball rise? ------------------------------------------------------------------------------------- A remote-controlled...
  43. P

    Kinematics problem, don't know how to find unknown variables

    Homework Statement A rocket is shot straight up with an initial speed at 500 m/s. Homework Equations The equations the teacher went over beforehand were Yf = 1/2 A(T)^2 + Vi(T) + Yi Vf = A(T) + Vi The Attempt at a Solution So far I have Vf = (-9.8)(T) + 500 m/s Yf = 4.9T2 +...
  44. M

    Kinematics involving two balls travelling at opposing directions

    Homework Statement A blue ball is thrown upward with an initial speed of 20.4 m/s, from a height of 0.5 meters above the ground. 2.5 seconds after the blue ball is thrown, a red ball is thrown down with an initial speed of 9.8 m/s from a height of 23.9 meters above the ground. The force of...
  45. A

    Basic Kinematics Questions, first year physics

    An object's motion can be described by a function that relates its position x (in meters) to time t (in seconds). Let this function be x = 6t2 + 2t + 4 What is this object's acceleration? I tried inputting 6, but it counted it wrong...
  46. 3

    Complex physics kinematics problems help

    Complex physics kinematics problems help! I'm having difficulty with these physics problems. I would really appreciate it if someone could help me. Homework Statement 1) Steven throws a rock off a cliff, giving it a velocity of 8.3 m/s [down). He heard the splash when the rock hit the...
  47. S

    Kinematics: Constant Acceleration

    A badminton shuttle, or "birdie" is struck, giving it a horizontal velocity of 73m/s [W]. Air resistance causes a constant acceleration of 18m/s^2 [E]. Determine its velocity after 1.6s. I've used the equation V2=V1+ax x t V2= Final velocity V1=initial velocity A= Acceleration t=time...
  48. H

    Calculating Average Velocity of a Moving Train: Solving Kinematics Problem

    Hello, I have problem with this example. I don't speak English very well, so please forgive me if something isn't quite enough defined - as it should be in English Physics terminology. The train moves from the station with an acceleration a. After reaching velocity v moves farther with...
  49. J

    2-D Kinematics: Distance of Rocket from Launch Pad

    Homework Statement A model rocket is launched from rest with an upward acceleration of 6.00m/s^2 and, due to a strong wind, a horizontal acceleration of 1.50m/s^2. How far is the rocket from the launch pad 6.00s later when the rocket engine runs out of fuel? Homework Equations Not sure..The...
  50. I

    Can Velocity Be Negative When Acceleration Is Positive?

    Is it possible for velocity to be negative while the acceleration is positive? If so, then how is it possible?
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