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Updated 23 Feb 2026
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Understanding Balanced and Unbalanced Forces: Effects on Motion
1 / 7
What Are Forces?
Think of forces as invisible pushes and pulls that are constantly acting on everything around you. You can't see them, but you definitely see what they do - like when you push a door open or gravity pulls your phone to the ground when you drop it.
Forces are measured in Newtons (N), named after Sir Isaac Newton. Every time something starts moving, stops, speeds up, or changes direction, it's because of forces doing their job.
The big idea here is simple: balanced forces keep things as they are, whilst unbalanced forces create change. Master this concept and you'll understand why a book stays on your desk and why a football flies through the air when you kick it.
Key Insight: Forces might be invisible, but their effects are everywhere - from the friction that stops you sliding off your chair to the gravity that keeps your feet on the ground!
Balanced Forces - When Nothing Changes
Balanced forces are like a perfectly even tug-of-war - both sides pull with equal strength, so nobody moves. When forces acting on an object are equal in size but opposite in direction, they cancel each other out completely.
The magic number here is zero. When forces are balanced, the net force (the total of all forces) equals 0 N. This means the object's motion won't change at all.
Here's the tricky bit that catches loads of students: if something is already moving when forces become balanced, it doesn't stop - it keeps moving at the same speed in the same direction! Think of a car on cruise control on a straight motorway.
Take a book on your desk. Gravity pulls it down whilst the normal force from the desk pushes up with exactly the same strength. These balanced forces mean your book stays put instead of falling through the desk or floating to the ceiling.
Remember: Balanced forces don't always mean "not moving" - they mean "not changing motion"!
Unbalanced Forces - When Change Happens
This is where things get exciting! Unbalanced forces occur when the forces acting on an object aren't equal - one direction "wins" over the other. The net force is greater than 0 N, and that's when you see acceleration.
Acceleration doesn't just mean speeding up - it's any change in motion. Things can speed up, slow down, or change direction. All of these count as acceleration in physics.
Picture kicking a football. Before you kick it, the ball sits still because gravity downwards equals the ground's upward push. But when your foot applies a massive forward force, suddenly the forces become unbalanced.
Your kick creates a much bigger force than air resistance can provide in the opposite direction. The net force sends the ball flying forward, and that's unbalanced forces in action!
Test Tip: If you see acceleration happening, you know the forces must be unbalanced - no exceptions!
Working Out Net Force
Let's make this practical with some maths - don't worry, it's easier than it looks! You just need to add up all the forces, keeping track of which direction they're pushing or pulling.
Example 1: Sarah pushes a box right with 50 N, whilst Tom pushes left with 50 N. Net force = 50 N + = 0 N. The forces are balanced, so the box won't change its motion.
Example 2: Now Sarah pushes right with 80 N, and Tom still pushes left with 50 N. Net force = 80 N + = 30 N to the right. These unbalanced forces will accelerate the box rightward.
The trick is picking a direction as positive (usually right or up) and making the opposite direction negative. Then it's just simple addition and subtraction to find your net force.
Study Hack: Always draw arrows showing force direction - it makes the maths much clearer and helps avoid silly mistakes!
Common Mistakes and Key Points
Here's the mistake that trips up nearly everyone: thinking that moving objects always have unbalanced forces acting on them. That's completely wrong! A car travelling at steady speed on a straight road has perfectly balanced forces - the engine's push forward exactly equals friction and air resistance pushing back.
Unbalanced forces are only needed when motion changes. If something moves at constant speed in a straight line, the forces are balanced. It's only when things speed up, slow down, or turn that you need unbalanced forces.
Don't forget about invisible forces like friction and air resistance - they're always there, even if you can't see them. These forces often balance out the more obvious pushes and pulls.
The direction of your net force always matches the direction of acceleration. If the net force points left, the object accelerates left. If it points right, acceleration goes right too.
Exam Success: Remember that constant velocity (steady speed, straight line) always means balanced forces - this question appears on nearly every test!
Quick Revision Summary
Forces are pushes or pulls measured in Newtons (N). When they're balanced (equal and opposite), the net force is 0 N and motion doesn't change. When they're unbalanced (not equal), you get a net force greater than 0 N that causes acceleration.
To find net force, add all forces together, remembering that direction matters. Use positive for one direction and negative for the opposite.
Objects at rest have balanced forces. Objects moving at constant speed also have balanced forces. Only accelerating objects have unbalanced forces acting on them.
Final Tip: If you can remember that balanced forces mean "no change" and unbalanced forces mean "change happens", you'll ace this topic!
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Elisha
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This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
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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 S
iOS 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 Klich
Android 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.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE Knowunity AI. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
Understanding Balanced and Unbalanced Forces: Effects on Motion
Forces are everywhere - when you kick a football, sit on a chair, or even just stand still, forces are acting on you and everything around you. Understanding whether these forces are balanced or unbalanced helps explain why things move... Show more
What Are Forces?
Think of forces as invisible pushes and pulls that are constantly acting on everything around you. You can't see them, but you definitely see what they do - like when you push a door open or gravity pulls your phone to the ground when you drop it.
Forces are measured in Newtons (N), named after Sir Isaac Newton. Every time something starts moving, stops, speeds up, or changes direction, it's because of forces doing their job.
The big idea here is simple: balanced forces keep things as they are, whilst unbalanced forces create change. Master this concept and you'll understand why a book stays on your desk and why a football flies through the air when you kick it.
Key Insight: Forces might be invisible, but their effects are everywhere - from the friction that stops you sliding off your chair to the gravity that keeps your feet on the ground!
Sign up to see the contentIt's free!
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Balanced Forces - When Nothing Changes
Balanced forces are like a perfectly even tug-of-war - both sides pull with equal strength, so nobody moves. When forces acting on an object are equal in size but opposite in direction, they cancel each other out completely.
The magic number here is zero. When forces are balanced, the net force (the total of all forces) equals 0 N. This means the object's motion won't change at all.
Here's the tricky bit that catches loads of students: if something is already moving when forces become balanced, it doesn't stop - it keeps moving at the same speed in the same direction! Think of a car on cruise control on a straight motorway.
Take a book on your desk. Gravity pulls it down whilst the normal force from the desk pushes up with exactly the same strength. These balanced forces mean your book stays put instead of falling through the desk or floating to the ceiling.
Remember: Balanced forces don't always mean "not moving" - they mean "not changing motion"!
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Unbalanced Forces - When Change Happens
This is where things get exciting! Unbalanced forces occur when the forces acting on an object aren't equal - one direction "wins" over the other. The net force is greater than 0 N, and that's when you see acceleration.
Acceleration doesn't just mean speeding up - it's any change in motion. Things can speed up, slow down, or change direction. All of these count as acceleration in physics.
Picture kicking a football. Before you kick it, the ball sits still because gravity downwards equals the ground's upward push. But when your foot applies a massive forward force, suddenly the forces become unbalanced.
Your kick creates a much bigger force than air resistance can provide in the opposite direction. The net force sends the ball flying forward, and that's unbalanced forces in action!
Test Tip: If you see acceleration happening, you know the forces must be unbalanced - no exceptions!
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Working Out Net Force
Let's make this practical with some maths - don't worry, it's easier than it looks! You just need to add up all the forces, keeping track of which direction they're pushing or pulling.
Example 1: Sarah pushes a box right with 50 N, whilst Tom pushes left with 50 N. Net force = 50 N + = 0 N. The forces are balanced, so the box won't change its motion.
Example 2: Now Sarah pushes right with 80 N, and Tom still pushes left with 50 N. Net force = 80 N + = 30 N to the right. These unbalanced forces will accelerate the box rightward.
The trick is picking a direction as positive (usually right or up) and making the opposite direction negative. Then it's just simple addition and subtraction to find your net force.
Study Hack: Always draw arrows showing force direction - it makes the maths much clearer and helps avoid silly mistakes!
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Improve your grades
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By signing up you accept Terms of Service and Privacy Policy
Common Mistakes and Key Points
Here's the mistake that trips up nearly everyone: thinking that moving objects always have unbalanced forces acting on them. That's completely wrong! A car travelling at steady speed on a straight road has perfectly balanced forces - the engine's push forward exactly equals friction and air resistance pushing back.
Unbalanced forces are only needed when motion changes. If something moves at constant speed in a straight line, the forces are balanced. It's only when things speed up, slow down, or turn that you need unbalanced forces.
Don't forget about invisible forces like friction and air resistance - they're always there, even if you can't see them. These forces often balance out the more obvious pushes and pulls.
The direction of your net force always matches the direction of acceleration. If the net force points left, the object accelerates left. If it points right, acceleration goes right too.
Exam Success: Remember that constant velocity (steady speed, straight line) always means balanced forces - this question appears on nearly every test!
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Quick Revision Summary
Forces are pushes or pulls measured in Newtons (N). When they're balanced (equal and opposite), the net force is 0 N and motion doesn't change. When they're unbalanced (not equal), you get a net force greater than 0 N that causes acceleration.
To find net force, add all forces together, remembering that direction matters. Use positive for one direction and negative for the opposite.
Objects at rest have balanced forces. Objects moving at constant speed also have balanced forces. Only accelerating objects have unbalanced forces acting on them.
Final Tip: If you can remember that balanced forces mean "no change" and unbalanced forces mean "change happens", you'll ace this topic!
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We thought you’d never ask...
What is the Knowunity AI companion?
Our AI Companion is a student-focused AI tool that offers more than just answers. Built on millions of Knowunity resources, it provides relevant information, personalised study plans, quizzes, and content directly in the chat, adapting to your individual learning journey.
Where can I download the Knowunity app?
You can download the app from Google Play Store and 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.
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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 S
iOS 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 Klich
Android 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.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE Knowunity AI. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
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 S
iOS 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 Klich
Android 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.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE Knowunity AI. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user