What is Classical mechanics: Definition and 1000 Discussions

Classical mechanics is a physical theory describing the motion of macroscopic objects, from projectiles to parts of machinery, and astronomical objects, such as spacecraft, planets, stars, and galaxies. For objects governed by classical mechanics, if the present state is known, it is possible to predict how it will move in the future (determinism), and how it has moved in the past (reversibility).
The earliest development of classical mechanics is often referred to as Newtonian mechanics. It consists of the physical concepts based on foundational works of Sir Isaac Newton, and the mathematical methods invented by Gottfried Wilhelm Leibniz, Joseph-Louis Lagrange, Leonhard Euler, and other contemporaries, in the 17th century to describe the motion of bodies under the influence of a system of forces. Later, more abstract methods were developed, leading to the reformulations of classical mechanics known as Lagrangian mechanics and Hamiltonian mechanics. These advances, made predominantly in the 18th and 19th centuries, extend substantially beyond earlier works, particularly through their use of analytical mechanics. They are, with some modification, also used in all areas of modern physics.
Classical mechanics provides extremely accurate results when studying large objects that are not extremely massive and speeds not approaching the speed of light. When the objects being examined have about the size of an atom diameter, it becomes necessary to introduce the other major sub-field of mechanics: quantum mechanics. To describe velocities that are not small compared to the speed of light, special relativity is needed. In cases where objects become extremely massive, general relativity becomes applicable. However, a number of modern sources do include relativistic mechanics in classical physics, which in their view represents classical mechanics in its most developed and accurate form.

View More On Wikipedia.org
Recent contents Top users
  1. rudransh verma

    Two balls one thrown up and other down

    I think because both are launched with same speed so both have same KE. Since one is Thrown downwards it’s KE will increase but not that much as the body which is thrown upwards. Because it covers more distance so it gains more energy(the body thrown up). So 3rd option must be right.
  2. rudransh verma

    B To displace the Earth from its orbit

    We know that the centripetal force and the tangential velocity is responsible for the motion of Earth around sun. Newton’s second law says F=ma. If we all get together(whole population) in one place like parallel to the tangent to orbit and jump can we displace Earth from its orbit?
  3. rudransh verma

    B Is the final velocity of a Tossed tomato the same as its initial velocity

    When a tomato is thrown up with a velocity ##v_0## it’s kinetic energy is 1/2mv_0^2. It will stop at the top and then again comes back to the launch point where it’s kinetic energy will be same as before, 1/2mv_0^2. How is this possible? Also when we throw the tomato up how can you be so sure...
  4. rudransh verma

    B Work energy theorem by variable force

    Its Good to be Back! From Resnik, Fundamentals of physics: Consider a particle of mass m, moving along an x-axis and acted on by a net force F(x) that is directed along that axis. The work done on the particle by this force as the particle moves from position ##x_i## to position ##x_f## is given...
  5. rudransh verma

    B Defining Impulse: The Importance of a New Quantity in Physics

    Sometimes there are forces which act for very small time known as impulsive forces. We cannot measure such large forces acting in a very short time but we can ##\Delta p##. ##\Delta p=F\Delta t##.This quantity is defined as Impulse. Why do we keep introducing new quantities? When is a new...
  6. rudransh verma

    B Same case of Newton’s third law

    Previously I have posted two threads on Thread 'Monkey climbing up the rope' https://www.physicsforums.com/threads/monkey-climbing-up-the-rope.1012065/ and Thread 'Car's maximum acceleration on a road is proportional to what?'...
  7. rudransh verma

    B What Happens to a Ball's Energy When Thrown Upwards?

    What is going on when the ball is thrown up in the sky. It is pushed by a force F for some distance d. Then the object travels a distance s up in the sky before finally coming to a stop. So what is going on here? Is the force doing work for distance d or distance s (s>d)? I think change in...
  8. rudransh verma

    B About verification on Kinetic energy and work

    1. From resnik, Halliday “Kinetic energy K is energy associated with the state of motion of an object. The faster the object moves , the greater is the kinetic energy” If I am right this means that greater the kinetic energy, greater is its speed. 2. Force transfers energy to the body due to...
  9. rudransh verma

    Pulley and weights hanging from spring balance

    Net force acting downwards is ##5g-g=4g## in downward direction. Net force on pulley is ##2T-4g##. Weight measured by balance?
  10. rudransh verma

    Three weights and two pulley problem

    ##Net force=50-T2+T2-T1+T1-20=10a## ##a=3 m/s^2## I want to ask when we do this way rather than taking individual masses we can’t decide the direction of the system as we can when they are taken individually. So is it correct to just leave ##a## as it is and solve ?
  11. rudransh verma

    B What is tension and how does it affect a rope?

    I have gathered everything from post “Monkey climbing up the rope” about tension. Tension is basically a force that the rope applies back when it is under stress. It is an inward force. Tension T's direction at end points of rope where its attached to the body and ceiling is inwards. Tension is...
  12. rudransh verma

    B Understanding Momentum: The Relationship Between Mass, Velocity, and Force

    “Momentum is clearly a vector quantity. The following common experiences indicate the importance of this quantity for considering the effect of force on motion. 1. Suppose a light-weight vehicle (say a small car) and a heavy weight vehicle (say a loaded truck) are parked on a horizontal road. We...
  13. rudransh verma

    B Newton’s second law as one complete law

    https://www.feynmanlectures.caltech.edu/I_08.html Page 9-3. It says “In these terms, we see that Newton’s second law, in saying that the force is in same direction as the acceleration,is really three laws, in the sense that the components of force in the x, y,z directions is equal to the mass...
  14. rudransh verma

    Equilibrium of Two Blocks in a Wall System: A FBD Approach

    This problem is similar to what I have done before here. I think since the system is in equilibrium, that is both bodies are at rest, net force on each should be zero. So to balance the forces in all directions we need only friction forces on each in upward direction. So the force on B due to A...
  15. rudransh verma

    How Does Friction and Acceleration Affect Tension in a Three-Block System?

    Since no body accelerates so net force is zero. Force on each mass is zero. T1 and T2 both are 60N. Edit: since there is a force applied so there is acceleration on friction less surface.
  16. rudransh verma

    Coefficient of friction and normal force

    The answer should be no change but we know ##F=ma##. In this eqn when acceleration increases mass decreases for same force. So why not here? If normal is doubled ##\mu## should be halved.
  17. rudransh verma

    Does Acceleration Affect Tension in a Sphere and Car System?

    If I draw the fbd then some force will accelerate the car in horizontal direction which I think does not effect the string in vertical direction. So same tension regardless of acceleration. But we know it will increase. So what will be the correct physics behind it?
  18. rudransh verma

    What is the tension in a rope when a monkey accelerates up?

    I think the tension in the rope will be equal to its weight , mg. I want to ask what if the monkey accelerates up with acceleration a, then what will be the tension in the rope?
  19. rudransh verma

    Two Blocks, a Pulley and an Inclined Plane

    1. ##-f_k\cos\theta-T\cos\theta+F_n\cos\alpha=m_2a_x## 2. ##f_k\sin\theta+T\sin\theta+F_n\sin\alpha-m_2g=-m_2a_y## 3. ##T-m_1g=m_1a_y## I am unable to get anywhere. There are accelerations in x , y directions. I need the value of acceleration. Then I can simply use ##s=ut+\frac12at^2##
  20. rudransh verma

    Double Differentiation and Acceleration in a Four Pulley System

    We can differentiate twice the y displacement with respect to time t and get the acceleration of block B. $$a_B= \frac12 m/s^2$$. But I don’t think it’s that simple.
  21. rudransh verma

    Car's maximum acceleration on a road is proportional to what?

    Since the car starts from rest it’s accelerating. So, $$F_a-f_k=ma$$ $$F_a-\mu mg=ma$$ $$\frac{F_a-\mu mg}m=a$$ Now from second eqn, ##s=ut+\frac12at^2## $$s=\frac12\frac{F_a-\mu mg}mt^2$$ $$\frac{2sm}{F_a-\mu mg}=t^2$$ $$\sqrt{\frac{2sm}{F_a-\mu mg}}=t$$ I don’t think I am getting any where!
  22. rudransh verma

    Contact and electromagnetic force

    I don’t know what is contact force. Are friction and normal forces called contact forces? And we have to take the resultant of the two to get the net contact force?
  23. rudransh verma

    A system of two bodies and wall

    I think there is normal force from wall and applied force will balance each other but there is no counter force against mg.Both bodies will slip and fall. I am not sure.
  24. rudransh verma

    Three blocks pulled by a force

    $$a= -40/(10+6+4)$$ $$a=-2 m/s^2$$ Taking one mass of 10 kg. $$T-40=10(-2)$$ $$T=20 N$$ This is correct. But if I make the eqn of the system then $$-40+T-T+T-T=20(-2)$$ I have also drawn the diagram. It looks like the second body m2 is subject to no force. But it’s accelerating. How?
  25. rudransh verma

    B Understanding Friction: Causes and Applications in Physics

    I read friction is the vector sum of the forces acting between the atoms of one surface and another. But the direction of friction is parallel to surface. I don’t get how friction occurs. I will also add the paragraph from my book “resnik” for further clarification. Other question is...
  26. rudransh verma

    Exploring the Advantage of Using Pulleys in Two Block Problems

    ##(T-m1g)-(T-m2g)=(m1+m2)a## But I think this is wrong eqn.
  27. rudransh verma

    B Atwood machine -- Question about the pulley and weights

    I want to ask in this machine when there are two masses hanging down then the tension T is directed upwards along the rope. Is it the force applied by the rope on the mass? Is it the force applied by the pulley? When the anyone mass of the machine moves downwards is it because the force of...
  28. rudransh verma

    Can You Solve This Motion Problem Using a Simple Trick?

    ##v^2=u^2+2as## ##v=10m/s## Again ##v^2=u^2+2as## ##a=25 m/s^2## So ##F=(200*25)/1000## ##F=5 N## Wrong answer!
  29. rudransh verma

    A Projectile problem -- Time to reach 1/3 of the max height

    Assuming it’s one body whose initial speed is u. First it attains height h then H. t1 and t2 are two times at which they attain h and H. ##h=ut1-\frac12gt1^2## ##H=ut2-\frac12gt2^2## ##\frac {t1}{t2}=1/3## Replacing t2 with 3t1, I am stuck.
  30. rudransh verma

    How Does Acceleration Affect Velocity in 1D Motion?

    ##v=\frac12 *1*4+\frac12*1*4= 4 m/s## but the answer is wrong.
  31. rudransh verma

    Integration of velocity to get displacement

    Integration of v= integration of##(alpha \sqrt x)dx##. But I am getting wrong answer.
  32. rudransh verma

    Understanding Distance and Displacement on Velocity-Time Graphs

    3) and 4) is easy. Average and instantaneous acceleration is same from 1 to 4 sec since it’s constant acceleration. 1) and 2) I am unable to get the correct area under the curve. ##s = \frac 12*(-5)*1 + \frac12*10*2 + 10*1 + \frac12*10*1## Same I guess will be distance. 5) what is the graph...
  33. rudransh verma

    Why do we use area under the curve to find displacement in particle motion?

    I calculated v=0 at t=3. s(3) =24 m. s(5)=16 m. So reverse distance that the particle travelled=24-16=8 m. So total distance =24+8=32 m.
  34. rudransh verma

    B Speed/velocity as a derivative

    [Note: Link to the quote below has been pasted in by the Mentors -- please always provide attribution when quoting another source] https://www.feynmanlectures.caltech.edu/I_08.html Let s=16t^2 and we want to find speed at 5 sec. s = 16(5.001)2 = 16(25.010001) = 400.160016 ft. In the last...
  35. Dario56

    I Action in Lagrangian Mechanics

    Lagrangian mechanics is built upon calculus of variation. This means that we want to find out function which is a stationary point of particular function (functional) which in Lagrangian mechanics is called the action. To know what this function is, action needs to be defined first. Action is...
  36. rudransh verma

    B About Second equation of motion

    I was wondering how the second equation of motion produces negative displacements ##s= ut+\frac 12 at^2## . Is ##\frac12 at^2## kind of distance operator?
  37. T

    A Noether's theorem time invariance -- mean value theorem use?

    how does the first step use mean value theorem? I don't get it , can anyone explain , thanks.
  38. brochesspro

    Roundtrip by Plane: Understanding Wind & Velocity Effects

    The question I have is that if the aero plane is traveling in the same direction as the wind, would it not increase its velocity, as in with boats and streams? So, if by chance, ##w = v##, then the velocity of the aero plane would double. It feels weird as going by the same logic, if the speed...
  39. brochesspro

    Find the unit vectors perpendicular to the given vectors

  40. mattlfang

    A bullet collides perfectly elastically with one end of a rod

    A bullet with mass m, velocity v perfectly elastically, vertically collide with one end of a rod on a slippery plane and the bullet stops moving after the collision. Find the mass of the stick M the bullet stops moving after an elastic collision, so all energy is transformed to the rod. There...
  41. P

    B Confused about force body diagram for 2 body collision

    I'm trying to understand Newton's third law in the context of collisions. Assume that one body has mass M kg and is traveling in the positive x direction with acceleration A m/s^2. Assume that the second body has mass m kg and is traveling in the negative x direction with acceleration a m/s^2...
  42. rudransh verma

    B How do mechanical (weighing) scales work?

    I want to understand how the weight machines work that we use in homes and shops. I have been working on force and motion chapter and I was curious how this weight machine actually push up and how it applies force to the feet of the person being weighed? What reading is this that we see in...
  43. tworitdash

    A Applications of weak measurement of quantum mechanics in other domains

    This is a surface level question and I don't want to go into detail. Imagine an algorithm which when used with a sensor output gives the statistical moments of a variable in nature (for example mean and standard deviation of a variable). The sensor measures this once in a while (like once in a...
  44. R

    Boats in a triangle colliding after some time

    Assume that three boats, ##B_1##, ##B_2## and ##B_3## travel on a lake with a constant magnitude velocity equal to ##v##. ##B_1## always travels towards ##B_2##, which in turn travels towards ##B_3## which ultimately travels towards ##B_1##. Initially, the boats are at points on the water...
  45. rudransh verma

    What are the forces at play in an elevator cab?

    I mentioned answers above in the question.
  46. rudransh verma

    B A question from Resnik about g-force

    Suppose there is one force gravitational force ##\vec{f_g}##. We can relate this downward force and downward acceleration with Newton sec law. This law can be written as ##F_{net,y}=ma_y## which becomes $$-F_g=m(-g)$$ or $$F_g=mg$$ $$\vec{F_g}=-F_g \hat j=-mg \hat j=m\vec g$$. Is it right...
  47. rudransh verma

    Confusion with force components

    x component of ##F_3## ##F_{3x}= m a_x- F_{1x}-F_{2x}## = ##ma\cos 50-F_1\cos(-150)-F_2\cos90## y component of ##F_3## ##F_{3y}= m a_y-F_{1y}-F_{2y}## =##ma\sin50-F_1\sin(-150)-F_2\sin90## And so on… My question how we can represent it in diagram ##F_1\sin(-150)##. I suppose...
  48. brochesspro

    Relative Velocity of a Passenger Hitting the Dashboard in a Car Crash

    Where exactly have I gone wrong? I think it is the part where I assume that the person gains the deceleration of the car, but I have no other way to proceed in this case. Also please only use the equations that I have posted below, and it would help if you would not use the equation for...
  49. rudransh verma

    Understanding the Use of the Long Jump Formula R=9.21m and Its Derivation

    $$R=9.21 m$$ $$Difference = 9.21-8.95$$ $$D=0.26m$$ My question is when do we use the formula for R given above. Because we could have calculated the Rmax by ##R=(v0\cos(\theta))t## and then subtracted R from it to get the answer. Why the x and y component in the derivation of this (R)formula...
  50. rudransh verma

    A stone projectile hitting the target

    $$(y-y0)=ut-1/2gt^2$$ $$y= -1/2gt^2$$ $$t^2=-1/98$$ If I get t I will be able to solve for x=ut
Back
Top