Net Force Formula: Meaning, Types, and Examples

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Net Force Formula is FNet = Fa + Fg + Ff + FN (Where, F1, F2, F3…FN is the force acting on a body). Net force is the sum of all the forces acting on an object together. A net force can accelerate a mass. Some other forces act on any person at rest or in motion. The term ‘net force’ is used in systems with multiple forces.

  • A force is pushing or pulling anything caused by the connection of an object with another object.
  • Without force, nothing can move, stop or change course.
  • It is a quantitative communication between two real entities between an article and its present circumstances. There are different types of energies in nature.
  • Assuming an object is in its state of motion then its current state will be either stationary or in motion. Its position can change assuming it is pushed or pulled. 
  • An external pressure or pull applied to an object changing its current state of motion is known as a force.

Key Terms: Net Force, Applied force, Gravitational Force, Frictional force, Net Force Formula, Types of Forces


What is Net Force?

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Net force is the sum of all forces acting on an object in a single plane. The net force is important because it helps describe the motion of an object and can be used to determine acceleration.

Newton's first law of motion explains that an object in motion will remain in motion and an object at rest unless acted upon by an unbalanced net force. Forces that move backward or downward are generally considered negative and forces that move forward or upward are considered positive. The sum of these forces equals the net force.

Net Force

Net Force


Magnitude of Net Force

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The magnitude of the net force is how large the net force is, which is different from the direction of the net force.

  • It is a numerical value assigned to force measured in the unit newton (N).
  • The magnitude of the net force is important because it indicates how much force is acting on the object and thus how much acceleration the object will experience.
  • For example, a net force of 1N will have much less impact on an object than a net force of 100N.

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Types Of Forces

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A force is a real cause that can meaningfully change the state of motion of any object or aspect. Various types of forces are noted below,

  • Contact Forces: Contact forces are the forces that occur when we apply for work on an object.
  • Non-Contact Forces: Non-contact forces are forces that occur without connection or contact, other than distance.
  • Spring Force: This force acts against the dispersion of molecules. Like spring or flexible elastic bands and so on.
  • Gravitational Force: Gravitational force is defined as the force acting between objects because of the presence of matter.

Net Force Formula

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When N = the number of forces acting on a body, the formula of the net force is

FNet = F1 + F2 + F3 ....+ FN

Where F1, F2, and F3 as the forces acting on the body.

When a body is at rest, the formula of the net force is

FNet = Fa + Fg

Where,

  • Fa = Applied force
  • Fg = Gravitational force

A net force is when a body is in motion and many forces act on it such as gravitational force Fg, frictional force Ff and normal force.

Therefore, the formula of the net force will be,

FNet = Fa + Fg + Ff + FN

Where,

  • Fa = Applied Force
  • Fg = Gravitational Force
  • Ff = Frictional Force
  • FN = Normal Force Acting

As per Newton's second law of motion, for an object to accelerate, some force must be the net force acting on it. Conversely, we can say that the object will accelerate if a net force acts on that object. The magnitude of the net force acting on an object can be calculated as the product of the mass of the object times the acceleration of the object. Hence,

FNet = m × a


Things to Remember

  • The net force is the force that is the sum of all the forces acting on an object together.
  • Newton's first law of motion explains that an object in motion will remain in motion and an object at rest unless acted upon by an unbalanced net force.
  • The magnitude of the net force is how large the net force is, which is distinct from the direction of the net force. It is a numerical value given to force estimated in the unit newton (N).
  • Various types of forces are Contact forces, Non-Contact forces, Spring forces, and Gravitational forces.
  • The formula of the net force is FNet = Fa + Fg + Ff + FN, where Fa = applied force, Fg = gravitational force, Ff = frictional force, and FN = Normal force acting.

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Sample Questions

Ques. In a tug of war, a fat man pulls on one side with a force of 100 N, and a lean man pulls on the other side with a force of 90 N. Decide the net force. (3 Marks)

Ans: Given,

Force F1= 100 N

Force F2 = -90 N

The net force formula is given by

FNet = F1 + F2

FNet = 100 – 90

FNet = 10 N

Hence, the net force is 10 N.

Ques. A toy car is at rest, and a force of 70 N is applied to it. If the frictional force is 20 N, define the net force. (3 Marks)

Ans: Given,

Applied force Fa = 70 N

Frictional force Ff = -20 N

The formula net force is

FNet = Fa + Ff

FNet = 70 – 20

FNet = 50 N

Hence, the net force is 50 N.

Ques. In a game of tug of war, a fat man pulls from one side with a force of 100 N, and a lean man pulls from the other side with a force of 90 N. What will be the net force? (3 Marks)

Ans: Given,

Force F1 = 100 N

Force F2 = 90 N

The formula of the net force is

FNet = F1 + F2

FNet = 100 + (-90)

FNet = 10 N.

Hence, the net force is 10 N.

Ques. A truck is stationary and a force of 70 N is applied to it. If the frictional force is 20 N, what will be the net force? (3 Marks)

Ans: Given,

Applied force Fa = 70 N

Frictional force Ff = 20 N

The formula of the net force is

FNet = Fa + Ff

FNet = 70 + (-20)

FNet = 50 N

Hence, the net force is 50 N.

Ques. Answer the following: (4 Marks)
(1) If the net force on the car is 3000 newtons, and the mass of the car is 1000 kg, what is the acceleration of the car?
(2) Find the net force on a car with a mass of 1200 kg and an acceleration of 4 m/s2.
(3) If an object is in equilibrium and the object is in motion, what can be said about the net force on the object? What can be stated about the acceleration of the object? What can be said about the speed with which the object is moving?

Ans:

  1. Using the formula

FNet = ma

We have:

3000 = 1000a

3 = a

Hence, the acceleration of the car is 3 m/s2.

  1. Using the formula

FNet = ma

with a = 4 and m = 1200, we have

FNet = 1200(4)

FNet = 4800

Hence, the value of the net force on the car is 4800 Newtons.

  1. If an object is in equilibrium, its net force is zero by definition. As the object is in equilibrium, it does not accelerate, and therefore a = 0. Since the object is in motion but has an acceleration of 0, the object must be moving at a constant speed.

Ques. Consider a block resting on the floor. If this block is balanced by 10 N of normal force and 10 N of gravitational force, what is the value of the net force acting on this block? (3 Marks)

Ans: Given,

Normal force acting on a block, FN = 10 N

Force of gravity acting on a block, Fg = -10 N (downward)

the value of net force acting on a block, Fnet =?

Applying the net force formula, (when the object is at rest)

Fnet= FN + Fg

Fnet = 10 – 10

Fnet = 0 N

Hence, the value of the net force acting on the block is 0 N.

Ques. An object has fallen on the table. If a force of 10 N is applied to this book, a frictional force of 8 N acts on it in the opposite direction. If this object is balanced by 25 N of the normal force and 25 N of the gravitational force, compute the value of the net force acting on it. (3 Marks)

Ans: Given,

The applied force acting on the object, Fa = 10 N

Friction force acting on the object, Ff = – 8 N (left)

Normal force acting on the object, FN = 25 N

Force of gravity acting on the object, Fg = – 25 N (downward)

the value of net force acting on the object, Fnet =?

Applying the net force formula, (when an object is in motion)

Fnet = Fa + Ff + FN + Fg

Fnet = 10 – 8 + 25 – 25

Fnet = 2 N

Hence, the value of the net force acting on the object is 2 N.

Ques. The vehicle is at rest, and a force of 100 N is applied to it. If the value of frictional force acting on it is 50 N, compute the net force. (3 Marks)

Ans: Given,

Applied force Fa = 100 N

Frictional force Ff = -50 N

The formula of the net force is

FNet = Fa + Ff

FNet = 100 – 50

FNet = 50 N

Hence, the net force is 50 N.

Ques. A bus gets stuck in the street and 8 people are pushing the bus in the right direction. All 8 persons push the bus with the following forces: 3N, 4N, 5N, 3N, 7N, 4N, 6N, and 2N. Compute the total net force applied on the bus. (4 Marks)

Ans:

  1. Force acting on the bus, F1 = 3 N
  2. Force acting on the bus, F2 = 4 N
  3. Force acting on the bus, F3 = 5 N
  4. Force acting on the bus, F4 = 3 N
  5. Force acting on the bus, F5 = 7 N
  6. Force acting on the bus, F6 = 4 N
  7. Force acting on the bus, F7 = 6N 
  8. Force acting on the bus, F8 = 2N

Net force acting, Fnet =?

Applying the net force formula of N forces acting upon, 

Fnet = F1 + F2 + F3 + F4 + F5 + F6 + F7 + F8

Fnet = 3 + 4 + 5 + 3 + 7 + 4 + 6 + 2

Fnet = 34 N

Hence, the value of the net force acting on the car is 34 N.

Ques. Two individuals A and B are pulling a rope from opposite ends. Individual A (who stands on the right side) pulls the rope with a force of 35 N and individual B (who stands on the left side) pulls the rope with a force of 25 N. Compute the value of net force acting on the rope. (3 Marks)

Ans: Given,

Force acting on the rope, F1 = 35 N

Force acting on the rope, F2 = -25 N (left)

The value of net force acting on the rope, Fnet =?

Applying the net force formula of N forces acting upon,

Fnet = F1 + F2

Fnet = 35 – 25

Fnet = 10 N

Hence, the value of the net force acting on the rope is 10 N.

Ques. An object is at rest, and a force of 90 N is applied to it. What will be the net force if a frictional force of 65 N acts on it? (2 Marks)

Ans: Given,

Applied force Fa = 90 N

Frictional force Ff = -65 N

The formula of the net force is,

FNet = Fa + Ff

FNet = 90 – 65

FNet = 25 N

Hence, the net force is 25 N.

Ques. A table rests on the floor. If this table is balanced by 20 N of normal force and 30 N of gravitational force, what is the value of net force acting on this table? (2 Marks)

Ans: Given,

Normal force acting on a table, FN = 20 N

Force of gravity acting on a table, Fg = -30 N (downward)

The value of net force acting on a table, Fnet =?

Applying the net force formula, (when the object is at rest)

Fnet = FN + Fg

Fnet = 20 – 30

Fnet = -10 N

Hence, the value of the net force acting on the block is -10 N.


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