We simply can describe the resultant force as the total force acting upon a body and this force acts in the direction of the body. Next, the net force is described as the sum of all forces acting on the body which is added by the individual vector forces. This is the basic notion for resultant force and net force
The resultant force is the sum of all the forces acting on the body with the torque associated and obtained by a system of forces acting on the body.
Resultant Force Concept
When several forces act upon the body, the force is replaced by a single force having the same effect called the resultant force.
Let’s consider a few examples for better understanding.
For instance, 20N of force pushes a car backward, and a force of 30N pulls the car forward; the resultant force is,
Fr = 30N-20N
Resultant force examples
A parachutist is falling from a height at a constant velocity. A force of 500N acts downwards on the parachutist due to gravity; also, he experiences an upward force of 500N at the same time due to air resistance. In this way, the forces are balanced.
The example is understood by a free-body diagram. In this diagram, the object is shown by a point, and different arrows show the forces. The length of the arrow indicates the magnitude, and the direction of the arrow indicates the direction of the force.
To understand this concept better a free-body diagram is used to describe the whole process and this diagram gives a clear view of what exactly is the logic behind the calculation of total forces acting on the body. This is explained along with an example.
Consider a plane flying up high and calculate the resultant force acting on the plane.
A circle shows a plane. Forces acting on the plane are depicted by using different arrows. Here, there are four different forces, namely, lift (upward force), thrust, backward drag (air resistance), and weight of the airplane pulled by gravity (downward force).
Since all these forces are vector forces, each of them must have magnitude and direction. To indicate the direction and the magnitude here we use arrows.
To which direction the arrow is pointed gives the direction of the force and how far the arrow travels gives the magnitude of the force. The forces here are acting in different directions canceling out each other, and at the end, what remains is calculated as the resultant force.
In order to calculate the resultant force, let’s deal with horizontal and vertical force components separately.
Considering the vertical component first we get,
The force is = 70,000N – 60,000N
Now the horizontal component is,
The force is = 1,10,000N – 80,000N
The resultant force is = 10,000N + 30,000N = 40,000N
Net Force Concept
As we all know that the force acts on an object zero when the object stays motionless unless any force is applied to it; also, there is no change in velocity or when the body is moving with constant velocity, in accordance with Newton’s First Law.
Suppose in order to accelerate an object; there must be a force to act upon. For instance, if a balling is falling on the ground has only the gravitational force, that is, the downward force, the length will tell the amount of force acting, and the velocity changes the direction of the force.
In another case, if there are multiple forces are acting upon this ball, like if the wind blows towards the right half as strong as the gravitational force due to the gravity pulling the ball downwards, then we need to add these forces using vector determination. Now the net force on the ball is evaluated.
Net Force Formula
The net force formula can be of two types, the one where the body is at rest and the one where the body is in motion.
Net force formula for a system when the body is at rest.
When the body is at rest, only the force applied and the gravitational force acts upon the body,
FNet = Faf + Fgf
Net force formula when the body is in motion, there are multiple forces acting on the body, here we take only a few to illustrate the formula.
FNet = Fag + Fgf + FF + FN
Where, Ff = frictional force; FN = normal force.
The net force has the ability to accelerate the mass, whereas other forces only act upon the body while at rest and in motion.
The basic formula for the net force is, FNet = F1 + F2 + F3 +…+ FN
Where, FN = number of forces.
Net force can also be calculated using Newton’s Second Law, F = ma. Since force is a vector quantity, it will have both the magnitude and the direction. And while calculating the net force, the force of the same magnitude and the opposite directions will cancel out.
In a system of forces, either horizontal or vertical components of force do not cancel out on each other; the system is said to have unbalanced forces existing. This can easily be identified from a free-body diagram.
For instance, we consider three such diagrams to find the net force of each system.
From these free-body diagrams, there seems to exist a net force that is acting upon the body. The net force is simply the complete forces existing in a body while at rest or in motion with unchanging velocity.
In all three cases, the net force is simply determined by adding the individual force vectors that are acting on the body.
Concluding this, now we come to a better understanding of how resultant force and the net force differ from each other, although with few similarities.