Engineering Mechanics

Types of Forces in Mechanics Explained for Students

Not all forces are the same. Gravity pulls you down without touching you. Friction only acts when two surfaces rub. A rope can pull but never push. Each of these behaves in its own way.

In mechanics we sort forces into clear groups so problems become easier to handle. Once you know which type of force you are dealing with, you know how to draw it and how to solve it.

In this lesson you will learn the main types of forces, starting with contact and non-contact forces, then moving to force systems like collinear, coplanar, concurrent, and parallel forces. By the end you will be able to name and classify any force you meet.

This builds on the last few lessons. Quick recall: a force is a push or a pull, it is a vector, and we draw it as an arrow.

What Are the Types of Forces?

A type of force is simply a category that groups forces by how they act.

There are two main ways to classify forces. The first is by whether the objects touch, giving contact and non-contact forces. The second is by how a group of forces is arranged in space, which gives us different force systems.

Both classifications are useful. Knowing them helps you pick the right method to solve a problem.

What Are Contact Forces?

A contact force is a force that acts only when two objects physically touch.

Think of pushing a table. Your hand must touch the table for the force to act. The moment you lift your hand, the force is gone. That is the sign of a contact force.

Common contact forces include:

  • Applied force, like pushing or pulling an object by hand.

  • Friction, which resists sliding between two surfaces.

  • Normal force, the support a surface gives to an object resting on it.

  • Tension, the pull inside a rope, cable, or string.

  • Spring force, the push or pull of a stretched or squeezed spring.

All of these need direct contact to exist.

What Are Non-Contact Forces?

A non-contact force acts from a distance, without the objects touching.

Gravity is the clearest example. The Earth pulls an apple down even though nothing connects them. The apple simply falls. This action across empty space is what makes it a non-contact force.

Common non-contact forces include:

  • Gravitational force, which pulls objects toward the Earth.

  • Magnetic force, which acts between magnets.

  • Electric force, which acts between charged objects.

These forces are sometimes called body forces because they act on the whole body at once, not just at the point of contact.

What Is a Force System?

A force system is a group of two or more forces acting on a body at the same time.

Real objects rarely have just one force on them. A parked car has gravity pulling down, the road pushing up, and maybe a hand pushing sideways. All of these together form a force system.

We classify force systems by how the forces are arranged. The main types are collinear, coplanar, concurrent, and parallel. Let us look at each.

What Are Collinear Forces?

Collinear forces act along the same straight line.

Picture a tug of war rope. Both teams pull along the very same line, just in opposite directions. Those pulls are collinear because they share one common line of action.

So the test for collinear forces is simple. If all the forces lie on a single line, they are collinear. This is the easiest force system to solve, because you can just add and subtract along that one line.

What Are Coplanar Forces?

Coplanar forces all act in the same flat plane.

Imagine several forces drawn on a sheet of paper. As long as every arrow stays on that flat sheet, the forces are coplanar. They may point in different directions, but they all share the same plane.

Most beginner problems in mechanics deal with coplanar forces because they are easier to draw and calculate. When forces leave the flat plane and act in three dimensions, we call them non-coplanar or spatial forces.

coplanar forces

What Are Concurrent Forces?

Concurrent forces all pass through a single common point.

Think of several ropes tied to one ring, each pulled in a different direction. Every rope pulls through that one ring. Because all the forces meet at the same point, they are concurrent.

This is a very common and useful case. When forces are concurrent, they cannot rotate the body, only push or pull it. That makes them simpler to solve, which is why concurrent force problems appear so often in exams.

What Are Parallel Forces?

Parallel forces act along lines that are parallel to each other. They never meet.

A good example is a table with a weight on each end. Both weights push straight down, along parallel lines. They point the same way but act at different places.

Parallel forces come in two kinds. Like parallel forces point in the same direction, such as two downward weights. Unlike parallel forces point in opposite directions. Parallel forces are important when studying beams and balancing.

What Are Non-Concurrent and Non-Coplanar Forces?

What Are Non-Concurrent and Non-Coplanar Forces

Not every force system is neat. Two more types cover the harder cases.

Non-concurrent forces do not meet at a single point. Because their lines do not cross at one place, these forces can both move and rotate a body, which makes the problem more involved.

Non-coplanar forces, also called spatial forces, act in three dimensions rather than a single flat plane. These need vector methods with x, y, and z components to solve. You will meet them later when problems become three dimensional.

Types of Forces with Examples

Let us tie it together with a single everyday scene, a book resting on a table while you push it sideways.

  • Gravity pulling the book down is a non-contact force.

  • The normal force from the table pushing up is a contact force.

  • Your sideways push is also a contact force.

  • Gravity and the normal force act along the same vertical line, so they are collinear.

  • All three forces act in the same flat plane, so they are coplanar.

One simple scene shows several types of forces at once. That is how mechanics works in the real world.

Where Do Engineers Use the Types of Forces?

Classifying forces is the first move in almost every real analysis.

Structural engineers identify parallel and coplanar forces when checking whether a beam is balanced. Mechanical engineers spot concurrent forces at joints and pins where several members meet. Recognising the type of force system tells the engineer which equations to use and how much work the problem will take.

When force systems become three dimensional and complex, engineers use simulation tools to handle them. That skill is developed in the FEA with ANSYS course.

Frequently Asked Questions

Q: What are the types of forces? A: Forces are mainly grouped as contact and non-contact forces. When several forces act together, they form force systems such as collinear, coplanar, concurrent, and parallel forces.

Q: What is the difference between contact and non-contact forces? A: Contact forces need the objects to touch, like friction and tension. Non-contact forces act from a distance, like gravity and magnetism.

Q: What are concurrent forces? A: Concurrent forces are forces that all pass through a single common point, such as several ropes tied to one ring.

Q: What is the difference between coplanar and non-coplanar forces? A: Coplanar forces all act in the same flat plane. Non-coplanar or spatial forces act in three dimensions and need x, y, and z components.

Q: What are parallel forces? A: Parallel forces act along parallel lines that never meet. Like parallel forces point the same way, and unlike parallel forces point in opposite directions.

Key Takeaways

  • Forces are first classed as contact or non-contact.

  • Contact forces need touch, such as friction, tension, and the normal force.

  • Non-contact forces act from a distance, such as gravity and magnetism.

  • A force system is a group of forces acting together on a body.

  • Collinear forces share one line, coplanar forces share one plane.

  • Concurrent forces meet at a point, and parallel forces never meet.

Quick Revision Box

  • Contact forces: applied, friction, normal, tension, spring

  • Non-contact forces: gravity, magnetic, electric

  • Collinear forces: act along the same straight line

  • Coplanar forces: act in the same plane

  • Concurrent forces: pass through one common point

  • Parallel forces: act along parallel lines (like or unlike)

  • Non-coplanar forces: act in three dimensions

Practice Corner

  1. What is the difference between a contact force and a non-contact force?

  2. Give one everyday example each of gravity, friction, and tension.

  3. Two teams pull a rope in opposite directions. What type of force system is this?

  4. Several cables tied to one hook pull in different directions. What are these forces called?

  5. What is the difference between like and unlike parallel forces?

Answers

  1. A contact force needs the objects to touch, while a non-contact force acts from a distance.

  2. Gravity: an apple falling. Friction: shoes gripping the floor. Tension: the pull in a rope while lifting a bucket. Other correct answers are fine.

  3. Collinear forces, since both pulls act along the same straight line.

  4. Concurrent forces, because they all pass through one common point.

  5. Like parallel forces point in the same direction, and unlike parallel forces point in opposite directions.

What's Next

Next we look at External Forces and Internal Forces, how loads act from outside a body and how the material resists them from inside.

Conclusion

Knowing the types of forces is like knowing the tools in a toolbox. Once you can tell whether a force is contact or non-contact, and whether a system is collinear, coplanar, concurrent, or parallel, you already know how to approach the problem. This simple habit of classifying forces makes every mechanics topic ahead much easier.

Want to sharpen these basics? Explore the free tools on the GaugeHow Learn Hub and test yourself with the Practice and MCQ tests.

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