What is Normal reaction: Definition and 28 Discussions

In mechanics, the normal force



{\displaystyle F_{n}\ }
is the component of a contact force that is perpendicular to the surface that an object contacts, as in Figure 1. In this instance normal is used in the geometric sense and means perpendicular, as opposed to the common language use of normal meaning "ordinary" or "expected". A person standing still on a platform is acted upon by gravity, which would pull them down towards the Earth's core unless there were a countervailing force from the resistance of the platform's molecules, a force which is named the "normal force".
The normal force is one type of ground reaction force. If the person stands on a slope and does not sink into the ground or slide downhill, the total ground reaction force can be divided into two components: a normal force perpendicular to the ground and a frictional force parallel to the ground. In another common situation, if an object hits a surface with some speed, and the surface can withstand the impact, the normal force provides for a rapid deceleration, which will depend on the flexibility of the surface and the object.

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  1. V

    How can the force of a normal reaction be electromagnetic?

    I do understand that gravitational the electromagnetic force between two electrons or protons is very large compared to the gravitational force between them. I can see this by looking at the equation of gravitational force (##F= \frac {Gm_1m_2} {r^2}##) and the equation of electrical force given...
  2. brotherbobby

    Pulling with and without a pulley

    Let me draw a free body diagram for the man. I assume that for both cases (a) and (b), the man pulls the block up with uniform velocity. (1) In case (a), realising that the man is in equlibrium (##\Sigma F = 0##) the normal reaction on the man ##N_a = w_M + T## is given by ##N_a = (50+25)\times...
  3. Svelte1

    Understanding Hinge Reactions: Debunking Common Misconceptions

    https://postimg.cc/JtP2h113 I think I may have forgotten some more basic elements of tension and normal reactions. I do not understand why the vertical component of the normal reaction =Tsin60-15g Because Tsin60-15g is negative when resolving upwards, i would have thought this meant that the...
  4. D

    Equilibrium : normal reaction of a rotational center?

    Homework Statement I'm trying to figure out the reaction at D,that's where the system can rotate. Problem: A force P of magnitude 90 N is applied to member ACDE, which is supported by a frictionless pin at D and by the cable ABE. Since the cable passes over a small pulley at B, the tension...
  5. T

    Kinetic energy & Conservation of energy

    Homework Statement You are driving with your car (of total mass: 1.2tonnes) with a speed of v=50km/h, until you see an obstacle. a) What is the kinetic energy of the car? b) When you start to brake, there is still 15m until the obstacle. What must be the size of the friction coefficient (µ)...
  6. JessiLim

    Static and Kinetic Friction vs Normal Reaction Graphing

    How do i suppose to determine the uncertainty for the slope of my Static friction against normal reaction graph? My data for static friction and normal force has the uncertainty of +/- 0.0001 The uncertainty is too small for me to draw airbox/bar in the graph to draw the max and min slope...
  7. V

    Why is the normal reaction force zero in the absence of any external force?

    Homework Statement My question is not a homework problem. I am having difficulty in understanding the concept oof contact forces. Homework Equations What I don't understand is that when two bodies A and B are in contact and left on a frictionless surface, they apply normal reactions on each...
  8. W

    B Actual value of normal reaction

    I am a high school student in Hong Kong studying Physics. I am having some problems about atmospheric pressure. Imagine there is a cube block with volume 1 m3 and top surface area 1 m2 . The cube block is being placed on the floor and it has mass of 1 kg. What is the normal reaction force F...
  9. S

    The normal reaction between blocks A and B is?

    Homework Statement 2. The attempt at a solution Let rightward acceleration of the block (A+B) be $$a$$. Let downward acceleration of block (A) be $$a'$$ down. For block A: $$mg-T=ma'$$ $$N+ma=0$$ For block B: $$T+N=Ma$$ On solving $$N=-\dfrac{m^2g}{M+2m}$$ by taking $$a=a'$$.But...
  10. physea

    Normal reaction in banked road circular motion

    Homework Statement Homework Equations ΣF=0 The Attempt at a Solution Basically I don't agree with this solution, I think it is R1 + R2 - mgcos5 + mv^2sin5/r = 0. Can you help me please? thanks!
  11. physea

    Normal reaction in banked road circular motion problem

    What is the equation of forces please for the axis parallel to the banked road? Is it R1+R2-mgcosθ=mV^2/r or R1+R2-mgcosθ=-mV^2/r? Can you advise me please?
  12. M

    Normal reaction force on banked track

    If a car us on a frictionless banked track what causes the normal reaction force to be greater than the weight force? My understanding from what I've read is that the vertical component of the reaction force cancels the weight force which makes sense as the object doesn't leave the ground. And...
  13. Titan97

    Finding Normal Reaction between Wedge and Block

    Homework Statement A block of mass m is kept on a smooth wedge of angle α and mass M which is in turn kept on a smooth floor. When the system is released from rest, calculate the force exerted by block on the wedge. Homework Equations None. The Attempt at a Solution Let the block a have a...
  14. J

    Normal reaction of a circulating object on a planet

    Why is the normal reaction of an object circulating a planet, equals to the gravitational force minus the centripetal force? I thought both gravitational force and centripetal force are directed towards the centre of the circular path i.e. in the same direction, therefore having, normal reaction...
  15. G

    What happens if the normal reaction force is less than zero?

    Homework Statement why the object will fall of when the normal reaction force is less than zero ? P/s : the normal reaction force is in downward direction... How if if the normal reaction force is less than zero ? the normal reaction is in upward direction ? Homework EquationsThe Attempt at a...
  16. G

    Direction of normal reaction of the Ferriw wheel at the high

    Homework Statement As you can see , the writer state that the direction of normal reaction force(R) is acted upwards , I have another book state that the normal reaction force (R) is acted downwards , which one is correct ? Homework EquationsThe Attempt at a Solution [/B]
  17. K

    Normal Reaction in the following cases

    Homework Statement A small block is shot into each of the four tracks as shown below. Each of the tracks rise to the same height. The speed with which the block enters the track is the same in all cases. At the highest point of the track, the normal Reaction is maximum in which track? 2...
  18. Jadaav

    Free body diagram - Weight and normal reaction

    Let's consider a stationary ball lying on the floor. The weight of the ball acts downwards and the normal reaction acts upwards. They are of the same magnitude but not of the same type. So normal reaction is the reaction to what, if not weight ?
  19. K

    Normal reaction, is this a concept we really understand?

    Hi guys ^^ I am still at A level physics, so don't flame me for my lack of knowledge Now i have been taught that for ex: We have a block of wood named A at rest on a perfectly smooth surface. If we analyse a free body diagram, we have a weight mg downwards acting on the block and a normal...
  20. 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...
  21. J

    Balancing Weight (mg): Exploring the Normal Reaction Force

    The weight (mg) is balanced by the normal reaction acting on the body. But What is the reason for this force(normal reaction)?
  22. M

    Normal reaction force of a roller to a wedge and the velocity

    Homework Statement http://img32.imageshack.us/img32/6505/p450.gif Cam mechanisms are used in many machines. For example, cams open and close the valves in your car engine to admit gasoline vapor to each cylinder and to allow the escape of exhaust. The principle is illustrated in Figure P5.66...
  23. V

    Normal reaction in a rolling object

    Why is the normal reaction to a rolling object shown to the side of the CM? Forces must be equal and opposite Is there a real problem if you assume it through the C?
  24. 1

    Inclined plane + Inclined force. Normal reaction force = ?

    ok I'm desperate now lol n this is my first time on PF. I've just had an exam and I'm sure i got this question wrong. But i'd like to know: the normal reaction force and the tension/Force F. The question is: There is this object that has a weight of 20N. It is on an inclined plane that is 30...
  25. R

    Inclined plane and normal reaction force

    A block of mass M slides down a frictionless plane inclined at an angle è with the horizontal. The normal reaction force exerted by the plane on the block is a Mg. b Mg sin è. c Mg cos è. d zero, since the plane is frictionless Homework Equations Fn=mg cos è The...
  26. S

    Ball bouncing on the floor - Normal reaction?

    Hey guys, Was just wondering if you could help me with what seems like a simple physics question. When a ball bounces on the floor, is the normal force greater than that of the weight, resulting in the bloor bouncing upwards? Or Is it the case where the normal reaction force is the...
  27. T

    Equilibrium normal reaction force problem

    Homework Statement http://tunerspec.ca/school/question3.gif The Attempt at a Solution This should be easy, but I'm tired and just can't do it. If anyone can point me in the right direction that'd be great. I tried making a FBD, and had the equations: Tsin30^{\circ} - 752N = 0 344N -...
  28. V

    Why Does a Ball Sink on Water Surface?

    Homework Statement Why does a ball placed on water surface sink, while one placed on the ground does not The Attempt at a Solution I think the ball sinks because mg is more than the upthrust (Vpg), but why doesn't the ball experience normal reaction (N=mg) on the water surface like...