net force

Examples of net force in the following topics:

• First Condition

  • The first condition of equilibrium is that the net force in all directions must be zero.
  • This means that both the net force and the net torque on the object must be zero.
  • Here we will discuss the first condition, that of zero net force.
  • For example, the net external forces along the typical x- and y-axes are zero.
  • There are horizontal and vertical forces, but the net external force in any direction is zero.

• Constant Velocity Produces a Straight-Line

  • If a charged particle's velocity is parallel to the magnetic field, there is no net force and the particle moves in a straight line.
  • There are many cases where a particle may experience no net force.
  • Or there could be two or more forces on the particle that are balanced such that the net force is zero.
  • If the net force on a particle is zero, then the acceleration is necessarily zero from Newton's second law: F=ma.
  • If the acceleration is zero, any velocity the particle has will be maintained indefinitely (or until such time as the net force is no longer zero).

• Two-Component Forces

  • In equilibrium, the net force and torque in any particular direction equal zero.
  • so objects with constant velocity also have zero net external force.
  • If no net force is applied to the object along the x-axis, it will continue to move along the x-axis at a constant velocity, with no acceleration .
  • A moving car for which the net x and y force components are zero
  • Calculate the net force and the net torque for an object in equilibrium

• Forces in Two Dimensions

  • In this simple one-dimensional example, without knowing the direction of the forces it is impossible to decide whether the net force is the result of adding the two force magnitudes or subtracting one from the other.
  • Associating forces with vectors avoids such problems.
  • When two forces act on a point particle, the resulting force or the resultant (also called the net force) can be determined by following the parallelogram rule of vector addition: the addition of two vectors represented by sides of a parallelogram gives an equivalent resultant vector which is equal in magnitude and direction to the transversal of the parallelogram.
  • Ideally, these diagrams are drawn with the angles and relative magnitudes of the force vectors preserved so that graphical vector addition can be done to determine the net force.
  • Forces are resolved and added together to determine their magnitudes and the net force.

• Translational Equilibrium

  • An object is said to be in equilibrium when there is no external net force acting on it.
  • In both cases – static or dynamic – net external forces and torques are zero.
  • A body is said to be in mechanical equilibrium when net external force is equal to zero and net external torque is also zero.
  • Since there is no net force on the object, the object does not accelerate.
  • In the second type, the object has a velocity, but since there are no net forces acting on it, the velocity remains constant.

• Second Condition

  • The second condition of static equilibrium says that the net torque acting on the object must be zero.
  • If a given object is in static equilibrium, both the net force and the net torque on the object must be zero.
  • The net force acting on the object must be zero.
  • Therefore all forces balance in each direction.
  • In equation form, the magnitude of torque is defined to be τ=rFsinθ where τ (the Greek letter tau) is the symbol for torque, r is the distance from the pivot point to the point where the force is applied, F is the magnitude of the force, and θ is the angle between the force and the vector directed from the point of application to the pivot point.

• Applications of Newton's Laws

  • Net force affects the motion, postion and/or shape of objects (some important and commonly used forces are friction, drag and deformation).
  • We know that a net force affects the motion, position and shape of an object.
  • Another interesting force in everyday life is the force of drag on an object when it is moving in a fluid (either gas or liquid).
  • Like friction, the force of drag is a force that resists motion.
  • We see an illustrated example of drag force in.

• Circular Motion

  • It states that an object will maintain a constant velocity unless a net external force is applied.
  • Therefore, uniform linear motion indicates the absence of a net external force.
  • Therefore, uniform circular motion indicates the presence of a net external force.
  • Consequently, the net external force $F_{\text{net}}$ required to sustain circular motion is:
  • Develop an understanding of uniform circular motion as an indicator for net external force

• Impulse

  • Impulse, or change in momentum, equals the average net external force multiplied by the time this force acts.
  • where F is the net force on the system, and Δt is the duration of the force.
  • change in momentum equals the average net external force multiplied by the time this force acts.
  • Forces are usually not constant.
  • A graph of force versus time with time along the x-axis and force along the y-axis for an actual force and an equivalent effective force.

• Internal vs. External Forces

  • Net external forces (that are nonzero) change the total momentum of the system, while internal forces do not.
  • Newton's 2nd law, applied to an isolated system composed of particles, $\bf{F}_{tot} = \frac{d\bf{p}_{tot}}{dt} = 0$ indicates that the total momentum of the entire system $\bf{p}_{tot}$ should be constant in the absence of net 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
  • Since all the external forces cancel out with each other, there are no net external forces.