What is Contact force: Definition and 43 Discussions

A contact force is any force that requires contact to occur. Contact forces are ubiquitous and are responsible for most visible interactions between macroscopic collections of matter. Pushing a car up a hill or kicking a ball across a room are some of the everyday examples where contact forces are at work. In the first case the force is continuously applied by the person on the car, while in the second case the force is delivered in a short impulse. Contact forces are often decomposed into orthogonal components, one perpendicular to the surface(s) in contact called the normal force, and one parallel to the surface(s) in contact, called the friction force.The microscopic origin of contact forces is diverse. Normal force is directly a result of Pauli exclusion principle and not a true force per se: Everyday objects do not actually touch each other; rather, contact forces are the result of the interactions of the electrons at or near the surfaces of the objects. The atoms in the two surfaces cannot penetrate one another without a large investment of energy because there is no low energy state for which the electron wavefunctions from the two surfaces overlap; thus no microscopic force is needed to prevent this penetration. On the more macroscopic level, such surfaces can be treated as a single object, and two bodies do not penetrate each other due to the stability of matter, which is again a consequence of Pauli exclusion principle, but also of the fundamental forces of nature: Cracks in the bodies do not widen due to electromagnetic forces that create the chemical bonds between the atoms; the atoms themselves do not disintegrate because of the electromagnetic forces between the electrons and the nuclei; and the nuclei do not disintegrate due to the nuclear forces.As for friction, it is a result of both microscopic adhesion and chemical bond formation due to the electromagnetic force, and of microscopic structures stressing into each other; in the latter phenomena, in order to allow motion, the microscopic structures must either slide one above the other, or must acquire enough energy to break one another. Thus the force acting against motion is a combination of the normal force and of the force required to widen microscopic cracks within matter; the latter force is again due to electromagnetic interaction. Additionally, strain is created inside matter, and this strain is due to a combination of electromagnetic interactions (as electrons are attracted to nuclei and repelled from each other) and of Pauli exclusion principle, the latter working similarly to the case of normal force.

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  1. G

    I Moment of inertia and contact force

    Two rotating cylinders are held in contact by a force F1. The force is applied through the center of one of the cylinders. One cylinder is the driving cylinder and the other is the driven cylinder . Does the moment of inertia of the system depends on the force contact force F1? Why? And...
  2. F

    Inconsistent problem about centrifugal/contact force

    This is problem 49 in chapter 6 of "Physics - 9th edition". A similar question was asked here several years ago (although with a different height). The figure is below. I added point A and angle \theta . The solution is pretty easy. For the purpose of my discussion I'm assuming that the height...
  3. P

    I Does the Normal contact force act through the centre of mass?

    Consider the following situation: You have 1 rectangular block lying on a table, and an identical block is placed above the block on the table. Now, this new block is constantly pushed to the right, right before it topples off. Consider the torque about an axis passing through the rightmost...
  4. jamiebean

    What is the contact force for a 20kg object with an acceleration of 2.7?

    I have watched a couple of videos regarding contact force, but I am still confused in solving this problem. which is its contact force? Fc=ma =20kg x 9.8=196N ?? then what's the acceleration a=2.7 for? im kind of self-taught right now.. my professor does not explain these simple questions...
  5. devilish_wit

    A question about contact forces and friction

    Homework Statement Two blocks of masses m1 and m2 are placed on a table in contact with each other as shown in the figure below. The coefficient of kinetic friction between the block of mass m1 and the table is μ1, and that between the block of mass m2 and the table is μ2. A horizontal force of...
  6. SirMarx01

    Automotive What is the compression force of a ring seated inside a cylinder

    Hello. I am finding out how many normal force between ring and cylinder. I try to find around for many hours but get noting. there are 8.2 mm inner diameters than put in 8.6 mm cylinder. The hardness of sealing element is 55 ShA. Contact area is 48.63 mm^2. I have data and drawing in attachment...
  7. R

    I How Do Attractive and Repulsive Electromagnetic Forces Combine in Contact Force?

    If friction is electromagnetically attractive force and the normal reaction is electromagnetically repulsive force which it obviously is. But how is it possible to have different type of force as the component of a single force i. e. Contact force over the nature of which I have got confused!
  8. Alexanddros81

    Calculate the contact force between the skis and the track

    Homework Statement 14.37 A 75-kg ski jumper starts his run in the position shown on the parabolic track. The equation of the parabola is ##y = (12/225)x^2##, where x and y are in meters. Neglecting friction, calculate the contact force between the skis and the track at O. Homework...
  9. J

    I Where is a contact force labeled on a diagram of a pivoted beam?

    Hi...What is a contact force and where is it labelled in a diagram showing a beam pivoted?
  10. D

    Contact force of block on a wall

    Homework Statement In this sketch, the mass m = 1.6 kg is pushed against a wall by force F, as shown, in the horizontal direction. The values of the coefficients of kinetic and static friction for the contact between are 0.81 and 0.84 respectively. The magnitude of F is slowly and continuously...
  11. H

    I Normal contact force for a sliding slope

    For the following question, how do we know that the acceleration of ##M## is constant over time? And is the normal contact force between the two masses smaller as compared to that where ##M## is fixed? The acceleration depends on the net force on ##M##, which depends on the normal contact...
  12. L

    Contact Force with two masses given

    Homework Statement A 3.0 kg and a 5.0 kg box rest side by side on a smooth, level floor. A horizontal force of 32 N is applied to the 3.0 kg box pushing it against the 5.0 kg box, and, as a result, both boxes slide along the floor. How large is the contact force between the two boxes? a) 32N...
  13. T

    Is Contact Force Responsible for Molecular Bending in Objects?

    Hello, When we have 2 bodies in contact with each other, for example a book lying on the surface of a table. The table's molecules bend a little bit because of the weight of the book thus producing the contact force. My question is this contact force acting on the book does also bend the...
  14. gracy

    Normal Contact Force Explained: What My Teacher Says

    My teacher says In case (A) there would be normal contact force between the blocks.But in case (B)There will not be any normal contact force between the blocks. I am really not getting this.I think The normal force is the support force exerted upon an object that is in contact with another...
  15. A

    Determine the magnitude of the contact force between the two blocks.

    Homework Statement Two blocks of masses m1 and m2, with m1 > m2, are placed in contact with each other on a frictionless, horizontal surface. A constant horizontal force is applies to m1. a) find the magnitude of the acceleration b) determine the magnitude of the contact force between the...
  16. S

    Finding the contact force in a hinge?

    I have been working on a slightly tricky calculus problem and was hoping someone could verify my solution. Homework Statement A 4m long beam whose mass is 5 kg is attached to the wall by a wire and a hinge that allows the beam to rotate. There is a sign (with a mass of 20 kg) attached to...
  17. T

    How do we get the formula for the contact force ?

    My teacher said there isn't a special kind of formula, you just derive it from f=ma. This is the diagram:
  18. D

    Out of curiosity how is the contact force forumla derived?

    Hello! I know that the contact force formula is Fc = F(m2/(m1+m2)) but I was wondering, how did this equation come into being? How is it derived? No this is not a homework question, I was just curious to know. Thanks!
  19. F

    Normal contact force with angles

    Homework Statement A small smooth ring R, of mass 0.6 kg, is threaded on a light inextensible string. One end of the string is attached to the fixed point A and the other end is attached to a ring B, of mass 0.2 kg, which is threaded on a fixed rough horizontal wire which passes through A...
  20. N

    Calculating Contact Force & Plate Stiffness of Composite Laminated Plate

    hi.. This is abdul I am carrying a impact of sphere on a composite laminated plate. i wanted to calculate the contact force when sphere impacts the plate.. or can anyone help me how to get the stiffness of plate.. or deflections in plate.. with respect to time Thanking you Your help will...
  21. M

    What is the contact force between the blocks?

    Homework Statement Two blocks are in contact on a frictionless, horizontal tabletop. An external force, F, is applied to block 1, and the two blocks are moving with a constant acceleration a = 2.45 m/s^2. Homework Equations what is the contact force between the blocks? The Attempt...
  22. H

    What is the maximum value of the contact force during the collision?

    Homework Statement The Figure shows an approximate representation of the contact force versus time during the collision of a 42-g tennis ball with a wall. The initial velocity of the ball is 35 m/s perpendicular to the wall; it rebounds with the same speed, also perpendicular to the wall...
  23. S

    Does normal contact force exert torque?

    I came across a question in which a cubical body of mass 'm', edge 'a' is slipping down an inclination with constant velocity and torque due to normal contact force is to be found about the centre of the block. As friction will exert an anticlockwise torque= 0.5amgsinx, where 'x' is the...
  24. B

    Calculating Normal Reaction & Contact Force on 800kg Van Attached to Car

    Homework Statement The following camping van with a total mass of 800 kg is connected at point P to the back of a car. The car accelerates with constant acceleration a during 4 seconds from rest until it achieves 60 km/h. Assuming there is no resistance (from air and ground), calculate the...
  25. I

    Newtons Law and Friction Question (along with a contact force question)

    Homework Statement Two crates, of mass 75 kg and 110 kg are in contact and at rest on a horizontal surface. A 620N force is exerted on the 75 kg crate. If the coefficient of kinetic friction is 0.15 calculate: a) the acceleration of the system b)the force that each crate exerts on the...
  26. J

    How Is Contact Force Calculated in Physics Problems?

    1. A student who's standing still on level ground weights 570 N and is wearing a backpack that is 81 N. a) What's the magnitude of net force on the student? b) What's the magnitude of the contact force on the student by the backpack? c) What's the magnitude of the contact foce on the...
  27. J

    Acceleration and magnitude of contact force

    Two blocks of masses m1 = 4.00 kg and m2 = 3.00 kg are placed in contact with each other on a frictionless horizontal surface. A constant force F = 9.00 N is applied to the block of mass m1. a) Determine the magnitude of the acceleration of the two-block system. b) Determine the magnitude of...
  28. K

    Net force on an object and contact force between objects

    Homework Statement "Three blocks (m1, m2 and m3) are in contact with each other on a frictionless, horizontal surface. A horizontal force is applied to m1. http://i4.photobucket.com/albums/y111/kathy_felldown/sb-pic0556.png What is the net force on block 1 and block 2? What is the...
  29. C

    Newton's Law's Problem (Contact Force)

    Basically 3 boxes, somehting like this; Masses are as followed: M1= 28 kg, M2= 18.7 kg, M3= 28.7 kg. The applied force on the box is 644 N Part A) What is the magnitude of the contact force between M1 and M2 Part B) What is the magnitude of the contact force between M2 and M3 To find...
  30. S

    Contact force, EM force and the loop

    The maximum I have found about contact force is very roughly this: it is nothing but electromagnetic force, meaning that, if two bodies collide, the electrons of the atoms of the outer shell of each body repel each other, those atoms displace towards their neighbours and repel them in turn, thus...
  31. P

    How to Calculate Contact Force Between Boxes in Physics?

    Homework Statement As shown in Figure 5-19, a force of magnitude 7.50 N pushes three boxes with masses m1 = 1.30 kg, m2 = 3.10 kg, and m3 = 5.80 kg. Figure 5-19 the figure depicts 3 boxes, in order m1, m2, m3 with a force pushing directly on m1 to the right on a flat level surface...
  32. B

    Calculating Magnitude of Contact Force Between Boxes 1 & 2

    Homework Statement A force of magnitude 9.00 N pushes three boxes with masses m1 = 1.30 kg, m2 = 2.80 kg, and m3 = 4.90 kg Find the magnitude of the contact force between boxes 1 and 2. Homework Equations Fnet,x = ma? The Attempt at a Solution I thought that it would be 9.00 N...
  33. R

    Calculating Contact Forces Between Three Blocks on a Frictionless Surface

    Homework Statement Three blocks on a frictionless horizontal surface are in contact with each other. A force F is applied to block A (mass mA ). If mA=mB=mC=10.0 kg and F = 96.0 N, determine the force of contact that each block exerts on its neighbor. Homework Equations The Attempt...
  34. A

    Find the Contact Force Between Two Blocks

    Two blocks are in contact on a frictionless table. A horizontal force F is applied to M2, as shown. If M1 = 1.51kg, M2 = 3.96kg, and F = 4.55N, find the size of the contact force between the two blocks. So first I found the acceleration (F=ma) 4.55/(1.51+3.96) = 0.83 = acceleration Im...
  35. S

    Find Contact Force Between 2 Blocks

    [SOLVED] Contact Force Homework Statement a.Two blocks are in contact on a frictionless table. A horizontal force F Is applied to M2. The force's magnitude is 4 N. [The diagram shows the force pushing on the left side of M2, which has M1 on its right side.]If M1=1.09 kg, M2=3.02 kg, find the...
  36. J

    Solving the Mountain Climber Problem: Tension & Contact Force

    Homework Statement A mountain climber is rappelling down a vertical wall. The rope attaches to a buckle strapped to the climber's waist 15 cm to the right of his center of gravity and makes an angle of = 15° with the wall. The climber weighs 780 N. (a) Find the tension in the rope N...
  37. T

    Calculate Contact Force: Car and Truck Collision on Icy Road

    Homework Statement A car of mass 8.50E+2 kg and a truck of mass 3.55E+3 kg run into one another due to ice on the road. 60.0 ms after the collision, the car is pushing on the truck with a force whose magnitude is 1.56671E+5 N. Calculate the size of the force on the car due to the truck at...
  38. M

    Tennis ball hitting a wall and rebounding - contact force

    A 57.0 g tennis ball with an initial speed of 25.2 m/s hits a wall and rebounds with the same speed. The figure below shows the force of the wall on the ball during the collision. What is the value of Fmax, the maximum value of the contact force during the collision, if the force is applied for...
  39. S

    Force Relationships: P + C = W

    A woman is straining to lift a large crate, without success. It is too heavy. We denote the forces on the crate as follows: P is the upward force being exerted on the crate by the person, C is the contact force on the crate by the floor, and W is the crate’s weight. How are the magnitudes of...
  40. Y

    What is the magnitude of the contact force between the boxes?

    I'm really confused about this problem - As shown in Figure 5-22, a force of magnitude 7.50 N pushes three boxes with masses m1 = 1.30 kg, m2 = 3.30 kg, and m3 = 5.10 kg. (a) Find the magnitude of the contact force between boxes 1 and 2. (b) Find the magnitude of the contact force...
  41. T

    Contact force in an ideal situation

    Assume I am holding a bar parallel to the ground. I let go of the bar and it lands on something at an arbitrary point on the bar before it hits the ground. How much force is dealt to the object (and bar)? This is the problem, but I'm going to simplify it to make a calculation possible. First...
  42. G

    Which direction does the normal contact force act?

    A ring of mass 0.3kg is threaded on a fixed, rough, horizontal curtain pole. A light inextensible string is attached to the ring. The string and the pole lie in the same vertical plane. The ring is pulled downwards by the string which makes an angle "A" to the horizontal, where tan A=3/4. The...