normal force

(noun)

Any force acting normal, to a surface, or perpendicular to the tangent plane.

Related Terms

Examples of normal force in the following topics:

  • Normal Forces

    • The normal force, $F_N$, comes about when an object contacts a surface.
    • This is the reason that the normal force exists.
    • The person remains still because the forces due to weight and the normal force create a net force of zero on the person.
    • When the elevator goes up, the normal force is actually greater than the force due to gravity.
    • The second is the normal force.

  • Physics and Engineering: Fluid Pressure and Force

    • Pressure is given as $p = \frac{F}{A}$ or $p = \frac{dF_n}{dA}$, where $p$ is the pressure, $\mathbf{F}$ is the normal force, and $A$ is the area of the surface on contact.
    • Mathematically, $p = \frac{F}{A}$, where $p$ is the pressure, $\mathbf{F}$ is the normal force, and $A$ is the area of the surface on contact.
    • It relates the vector surface element (a vector normal to the surface) with the normal force acting on it.
    • The subtraction (–) sign comes from the fact that the force is considered towards the surface element while the normal vector points outward.
    • The total force normal to the contact surface would be:

  • Banked and Unbacked Highway Curves

    • The components of the normal force $N$ in the horizontal and vertical directions must equal the centripetal force and the weight of the car, respectively.
    • The only two external forces acting on the car are its weight $w$ and the normal force of the road $N$.
    • (A frictionless surface can only exert a force perpendicular to the surface—that is, a normal force. ) These two forces must add to give a net external force that is horizontal toward the center of curvature and has magnitude $\frac{mv^2}{r}$.
    • Only the normal force has a horizontal component, and so this must equal the centripetal force—that is:
    • From the figure, we see that the vertical component of the normal force is $N\cos\theta$, and the only other vertical force is the car's weight.

  • Internal vs. External Forces

    • External forces: forces caused by external agent outside of the system.
    • There are mainly three kinds of forces: Gravity, normal force (between ice & pucks), and frictional forces during the collision between the pucks
    • With this in mind, we can see that gravity and normal forces are external, while the frictional forces between pucks are internal.
    • (Gravity and normal force on each puck have the same magnitude, but are in the opposite directions) Therefore, we conclude that the total momentum of the two pucks should be a conserved quantity.
    • Also note that, in the previous example, if we include the rest of the Earth in our system, the gravity and normal forces themselves become internal.

  • Problem-Solving With Friction and Inclines

    • Recall that the force of friction depends on both the coefficient of friction and the normal force.
    • $F_f = \mu F_n$ When on an incline with an angle $\theta$, the normal force becomes $F_n=mg\cos(\theta)$
    • If the frictional force is equal to the gravitational force the block will not slide down the incline.
    • If the maximum frictional force is greater than the force of gravity, the sum of the forces is still 0.
    • The force of friction can never exceed the other forces acting on it.

  • Friction: Kinetic

    • The force of friction is what slows an object sliding over a surface.
    • $F_n$ is called the normal force and is the force of the surface pushing up on the object.
    • In most cases on level ground, the normal force will be the equal and opposite of the object's weight.
    • Thus, a force is required just to set the object in motion.
    • Some of the peaks will be broken off, also requiring a force to maintain motion.

  • Friction: Static

    • Like kinetic friction, the force of static friction is given by a coefficient multiplied by the normal force.
    • The normal force is the force of the surface pushing up on the object, which is usually equal to the object's weight.
    • As with all frictional forces, the force of friction can never exceed the force applied.
    • Thus the force of static friction will vary between 0 and $_sF_n$ depending on the strength of the applied force.
    • Any force larger than that overcomes the force of static friction and causes sliding to occur.

  • First Condition

    • The forces acting on him add up to zero.
    • Both forces are vertical in this case.
    • There are horizontal and vertical forces, but the net external force in any direction is zero.
    • The applied force between the tires and the road is balanced by air friction, and the weight of the car is supported by the normal forces, here shown to be equal for all four tires.
    • The forces in all directions are balanced.

  • General Problem-Solving Tricks

    • N: the normal force of the ramp.
    • Ff: the friction force of the ramp.
    • The line of action of the normal force has been shown to be at the midpoint of the base but its true location can only be found if sufficient further data is given.
    • A force arrow should lie along the line of force, but where along the line is irrelevant.
    • These forces can be friction, gravity, normal force, drag, tension, etc...

  • Task Forces

    • A member in each organization may be assigned to the task force.
    • Once the task force members have achieved the defined objective, the task force dissolves.
    • There are instances, however, in which a task force can turn into a normal unit.
    • A task force is normally headed by someone of such high standing that he or she can make decisions without first consulting their superiors.
    • Task force members tend to come from different areas.