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15 Dec 2025
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GCSE Physics Guide: Key Topics and Concepts
Y
Yana ๐ ๐ฉโโ๏ธ
@yans26
1 / 6
Scalar and Vector Quantities
Think about giving directions to your mate - saying "walk 5 metres" isn't very helpful, but "walk 5 metres north" gets them where they need to go. That's the difference between scalar and vector quantities in physics.
Scalar quantities only have size (magnitude) - like distance, speed, mass, and temperature. You just need a number to describe them completely. Vector quantities need both size and direction - like displacement, velocity, acceleration, and force.
Forces are always vectors because they push or pull in specific directions. They come in two types: contact forces (like friction) where objects must touch, and non-contact forces (like gravity) that work across empty space. You can represent forces using arrows - longer arrows mean stronger forces, and the arrow points in the force's direction.
Quick tip: If you need to know "which way", it's probably a vector quantity!
Understanding Resultant Forces
In real life, multiple forces usually act on objects simultaneously, like when you're cycling against wind resistance whilst pedaling forward. The resultant force is the single force that has the same effect as all these forces combined.
When forces act in the same line, you simply add forces going the same way and subtract opposing forces. If the resultant force equals zero, the forces are balanced and the object won't change its motion - it'll keep doing exactly what it was doing before.
Free body diagrams help visualise all forces acting on an object. For more complex situations where forces don't act in straight lines, you can use the parallelogram rule to find the resultant force geometrically.
Remember: Zero resultant force doesn't mean no forces - it means all forces cancel each other out perfectly!
Work Done and Energy Transfer
When you push your bike up a hill, you're doing work in the physics sense - and that's why you get knackered! Work happens whenever a force makes an object move, and it always involves transferring energy.
The equation W = Fs tells you how much work is done. Work is measured in joules (J), where 1 joule equals the work done when 1 newton of force moves an object 1 metre. When you do work against friction (like air resistance), energy gets transferred to heat - that's why car brakes get hot.
Distance and displacement aren't the same thing. Distance is how far you actually travel (scalar), whilst displacement is the straight-line distance from start to finish (vector). If you run around a football pitch and end up where you started, your displacement is zero even though you've covered loads of distance.
Real-world connection: This is why sat-navs calculate different routes for "shortest distance" vs "quickest time"!
Newton's Three Laws of Motion
Newton's First Law explains why you slide forward when a bus brakes suddenly - moving objects keep moving unless a resultant force stops them. Stationary objects stay put for the same reason. This tendency to resist changes in motion is called inertia.
Newton's Second Law gives us the famous equation F = ma. More force means more acceleration, but heavier objects accelerate less for the same force. This is why it's harder to push a car than a shopping trolley with the same force.
Newton's Third Law states that forces always come in pairs - when you jump, you push down on the ground and it pushes back up on you with equal force. This isn't just about contact either; rockets work in space because the gases they push out push back on the rocket.
Memory trick: Every action has an equal and opposite reaction - think about walking, swimming, or even sitting in a chair!
Moments and Simple Machines
Ever noticed it's much easier to open a door by pushing near the handle rather than near the hinges? That's because of moments - the turning effect of forces around a pivot point.
The moment equation M = Fd shows that both the force size and distance from the pivot matter. For balanced objects like see-saws, clockwise moments equal anticlockwise moments. This principle helps you work out unknown forces or distances.
Levers and gears are simple machines that make work easier. Levers can be force multipliers (like bottle openers) or distance multipliers (like brooms). Gears work similarly - small gears driving large ones multiply force, whilst large gears driving small ones multiply speed.
Everyday example: Your bike gears use these principles - low gear multiplies your pedaling force for hills, high gear multiplies speed for flat roads!
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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
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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 didnโt even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as Iโm sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH ๐๐๐ฒ๐ค๐โจ๐๐ฎ
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 itโs 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 didnโt even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as Iโm sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH ๐๐๐ฒ๐ค๐โจ๐๐ฎ
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
GCSE Physics Guide: Key Topics and Concepts
Y
Yana ๐ ๐ฉโโ๏ธ
@yans26
Ever wonder why you can't push a door open by pressing right next to the hinges, or how a small gear can move something much heavier? Forces aren't just about pushing and pulling - they're about balance, direction, and clever... Show more
Scalar and Vector Quantities
Think about giving directions to your mate - saying "walk 5 metres" isn't very helpful, but "walk 5 metres north" gets them where they need to go. That's the difference between scalar and vector quantities in physics.
Scalar quantities only have size (magnitude) - like distance, speed, mass, and temperature. You just need a number to describe them completely. Vector quantities need both size and direction - like displacement, velocity, acceleration, and force.
Forces are always vectors because they push or pull in specific directions. They come in two types: contact forces (like friction) where objects must touch, and non-contact forces (like gravity) that work across empty space. You can represent forces using arrows - longer arrows mean stronger forces, and the arrow points in the force's direction.
Quick tip: If you need to know "which way", it's probably a vector quantity!
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Understanding Resultant Forces
In real life, multiple forces usually act on objects simultaneously, like when you're cycling against wind resistance whilst pedaling forward. The resultant force is the single force that has the same effect as all these forces combined.
When forces act in the same line, you simply add forces going the same way and subtract opposing forces. If the resultant force equals zero, the forces are balanced and the object won't change its motion - it'll keep doing exactly what it was doing before.
Free body diagrams help visualise all forces acting on an object. For more complex situations where forces don't act in straight lines, you can use the parallelogram rule to find the resultant force geometrically.
Remember: Zero resultant force doesn't mean no forces - it means all forces cancel each other out perfectly!
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By signing up you accept Terms of Service and Privacy Policy
Work Done and Energy Transfer
When you push your bike up a hill, you're doing work in the physics sense - and that's why you get knackered! Work happens whenever a force makes an object move, and it always involves transferring energy.
The equation W = Fs tells you how much work is done. Work is measured in joules (J), where 1 joule equals the work done when 1 newton of force moves an object 1 metre. When you do work against friction (like air resistance), energy gets transferred to heat - that's why car brakes get hot.
Distance and displacement aren't the same thing. Distance is how far you actually travel (scalar), whilst displacement is the straight-line distance from start to finish (vector). If you run around a football pitch and end up where you started, your displacement is zero even though you've covered loads of distance.
Real-world connection: This is why sat-navs calculate different routes for "shortest distance" vs "quickest time"!
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Newton's Three Laws of Motion
Newton's First Law explains why you slide forward when a bus brakes suddenly - moving objects keep moving unless a resultant force stops them. Stationary objects stay put for the same reason. This tendency to resist changes in motion is called inertia.
Newton's Second Law gives us the famous equation F = ma. More force means more acceleration, but heavier objects accelerate less for the same force. This is why it's harder to push a car than a shopping trolley with the same force.
Newton's Third Law states that forces always come in pairs - when you jump, you push down on the ground and it pushes back up on you with equal force. This isn't just about contact either; rockets work in space because the gases they push out push back on the rocket.
Memory trick: Every action has an equal and opposite reaction - think about walking, swimming, or even sitting in a chair!
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Moments and Simple Machines
Ever noticed it's much easier to open a door by pushing near the handle rather than near the hinges? That's because of moments - the turning effect of forces around a pivot point.
The moment equation M = Fd shows that both the force size and distance from the pivot matter. For balanced objects like see-saws, clockwise moments equal anticlockwise moments. This principle helps you work out unknown forces or distances.
Levers and gears are simple machines that make work easier. Levers can be force multipliers (like bottle openers) or distance multipliers (like brooms). Gears work similarly - small gears driving large ones multiply force, whilst large gears driving small ones multiply speed.
Everyday example: Your bike gears use these principles - low gear multiplies your pedaling force for hills, high gear multiplies speed for flat roads!
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We thought youโd 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?
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Is Knowunity really free of charge?
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Students love us โ and so will you.
4.9/5
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4.8/5
Google 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 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 itโs 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 didnโt even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as Iโm sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH ๐๐๐ฒ๐ค๐โจ๐๐ฎ
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 itโs 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 didnโt even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as Iโm sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH ๐๐๐ฒ๐ค๐โจ๐๐ฎ
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