Physics is all about understanding how objects move and interact.... Show more
Physics133 views·Updated May 22, 2026·2 pagesUnderstanding Physics: A Guide to Forces
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Understanding Forces and Free Body Diagrams
Forces are pushes or pulls that cause objects to accelerate. Several common forces affect objects in our daily lives. An applied force is what we create when we physically push or pull an object. The normal force acts perpendicular to a surface, pushing back when objects press against it. Frictional force opposes motion between surfaces in contact, while tension force is the pulling force transmitted through a string, rope, or cable.
Free Body Diagrams (FBDs) are visual tools that show all forces acting on an object. These diagrams help us see when forces cancel each other out or when they combine to create a net force. Remember, according to Newton's laws, an object accelerates only when there's a net force acting on it.
When drawing an FBD for a book resting on a table, we include two main forces: the gravitational force pulling down and the normal force pushing up. Since the book isn't moving, these forces must be equal in magnitude but opposite in direction, resulting in zero net force.
💡 When forces are balanced (equal and opposite), the net force is zero and the object won't accelerate—it will either remain at rest or continue moving at constant speed in a straight line.
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Applying Newton's Second Law
When a book slides across a table at constant speed, the applied force pushing it forward exactly balances the friction force pushing backward. Since these forces cancel out (making net force zero), the book maintains constant speed rather than accelerating.
For a heavier book sliding with increasing speed, the applied force must be greater than the friction force. This creates a net force in the direction of motion, causing the book to accelerate as it moves across the table.
Newton's Second Law gives us the equation F = ma, which means the net force equals mass times acceleration. This powerful formula lets us calculate unknown forces or predict an object's acceleration. For example, a 4.5 kg object accelerating at 5 m/s² experiences a force of 22.5 Newtons (N).
💡 Whenever you see an object accelerating, you can be certain there's a net force acting on it in the direction of acceleration. The size of this force determines how quickly the object's speed changes.
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Physics133 views·Updated May 22, 2026·2 pagesUnderstanding Physics: A Guide to Forces
Physics is all about understanding how objects move and interact. Forces are the pushes and pulls that cause objects to accelerate, and understanding them is key to explaining almost everything in the physical world around us.
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Understanding Forces and Free Body Diagrams
Forces are pushes or pulls that cause objects to accelerate. Several common forces affect objects in our daily lives. An applied force is what we create when we physically push or pull an object. The normal force acts perpendicular to a surface, pushing back when objects press against it. Frictional force opposes motion between surfaces in contact, while tension force is the pulling force transmitted through a string, rope, or cable.
Free Body Diagrams (FBDs) are visual tools that show all forces acting on an object. These diagrams help us see when forces cancel each other out or when they combine to create a net force. Remember, according to Newton's laws, an object accelerates only when there's a net force acting on it.
When drawing an FBD for a book resting on a table, we include two main forces: the gravitational force pulling down and the normal force pushing up. Since the book isn't moving, these forces must be equal in magnitude but opposite in direction, resulting in zero net force.
💡 When forces are balanced (equal and opposite), the net force is zero and the object won't accelerate—it will either remain at rest or continue moving at constant speed in a straight line.
2
of 2Sign up to see the content. It's free!
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Applying Newton's Second Law
When a book slides across a table at constant speed, the applied force pushing it forward exactly balances the friction force pushing backward. Since these forces cancel out (making net force zero), the book maintains constant speed rather than accelerating.
For a heavier book sliding with increasing speed, the applied force must be greater than the friction force. This creates a net force in the direction of motion, causing the book to accelerate as it moves across the table.
Newton's Second Law gives us the equation F = ma, which means the net force equals mass times acceleration. This powerful formula lets us calculate unknown forces or predict an object's acceleration. For example, a 4.5 kg object accelerating at 5 m/s² experiences a force of 22.5 Newtons (N).
💡 Whenever you see an object accelerating, you can be certain there's a net force acting on it in the direction of acceleration. The size of this force determines how quickly the object's speed changes.
We thought you’d never ask...
What is the Knowunity AI companion?
Our AI companion is specifically built for the needs of students. Based on the millions of content pieces we have on the platform we can provide truly meaningful and relevant answers to students. But its not only about answers, the companion is even more about guiding students through their daily learning challenges, with personalised study plans, quizzes or content pieces in the chat and 100% personalisation based on the students skills and developments.
Where can I download the Knowunity app?
You can download the app in the Google Play Store and in the Apple App Store.
Is Knowunity really free of charge?
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
Similar Content
Most popular content: Force
1Most popular content in Physics
9Most popular content
9Can't find what you're looking for? Explore other subjects.
Students love us — and so will you.
4.6/5App Store
4.7/5Google Play
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan SiOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha KlichAndroid user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
AnnaiOS user