Forces are everywhere around us - from the weight pulling... Show more
Physics
SociologySign up to see the contentIt's free!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
0
0
Maddie
14/12/2025
Physics
Physics - Forces
42
•
14 Dec 2025
•
Understanding Physics: Forces - AQA Combined Science
Maddie
@mads_lh
1 / 4
Physics - Forces
Vectors and scalars are the foundation of forces. A vector has both size and direction (like velocity and force), whilst a scalar only has size (like speed and mass). Think of vectors as arrows - the longer the arrow, the bigger the magnitude.
Forces are simply pushes or pulls between objects. Contact forces happen when objects touch (like friction when you rub your hands together), while non-contact forces work at a distance (like gravity pulling you towards Earth).
Weight isn't the same as mass - your mass stays constant, but your weight changes depending on the gravitational field strength. On Earth, weight = mass × 9.8 N/kg. The Moon has weaker gravity, so you'd weigh less there but have the same mass.
The resultant force is what you get when you add up all forces acting on an object. If forces balance out , the object either stays still or moves at constant speed. Unbalanced forces cause acceleration in the direction of the resultant force.
💡 Quick Tip: Work done = force × distance. When you push against friction, this energy becomes heat - that's why your hands warm up when you rub them together!
Springs and Motion Basics
Springs demonstrate how objects deform under force. Elastic deformation means the spring bounces back to its original shape - like a rubber band. Plastic deformation means it stays bent permanently, like a paperclip that's been twisted too far.
Hooke's Law shows that extension is directly proportional to applied force: F = k × e . This only works up to the limit of proportionality - push too hard and the spring breaks this rule.
When you stretch a spring, you're storing elastic potential energy. The energy stored equals ½ × k × e². This energy gets released when the spring returns to its original length.
Distance vs displacement and speed vs velocity are crucial distinctions. Distance and speed are scalars (no direction), while displacement and velocity are vectors (include direction). A car going round a roundabout might travel 100m distance but have zero displacement if it ends where it started.
💡 Quick Tip: Typical speeds to remember - walking , cycling , cars , and sound in air . These often appear in exam questions!
Graphs and Newton's Laws
Displacement-time graphs have velocity as their gradient. For curved lines, draw a tangent at any point to find the instantaneous velocity. Velocity-time graphs have acceleration as their gradient, and the area under the line gives you distance travelled.
A steeper gradient means greater acceleration, negative gradients show deceleration, and horizontal lines indicate constant speed. When the line is at zero velocity, the object is stationary.
Newton's First Law explains inertia - objects resist changes to their motion. A book on a table stays put, and a moving car keeps moving unless forces act on them. This is why you lurch forward when a car brakes suddenly.
Newton's Second Law gives us the fundamental equation: F = ma . Doubling the force doubles the acceleration, but doubling the mass halves the acceleration for the same force.
💡 Quick Tip: On velocity-time graphs, count the squares under the line to find distance travelled. Each square represents a specific distance based on the graph's scale.
Newton's Third Law and Vehicle Safety
Newton's Third Law states that every action has an equal and opposite reaction. When you walk, you push backwards on the ground, and the ground pushes you forwards. The forces are equal in size but opposite in direction.
Stopping distances involve two parts: thinking distance (how far you travel while reacting) and braking distance (how far you travel while slowing down). Stopping distance = thinking distance + braking distance.
Thinking distance increases with speed, tiredness, alcohol, drugs, and distractions. Braking distance increases with speed, wet/icy roads, worn tyres, and faulty brakes. Typical reaction times range from 0.2 to 0.9 seconds.
Momentum is always conserved in collisions and explosions. The total momentum before equals the total momentum after, assuming no external forces like friction interfere. This principle explains everything from car crashes to rocket launches.
💡 Quick Tip: Remember that momentum is a vector - direction matters! In head-on collisions, the momentums are in opposite directions, so you subtract rather than add them.
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.
Most popular content in Physics
Most popular content
English - inspector calls quotes and analysis
Quotes from every main character
English Literature10
Can't find what you're looking for? Explore other subjects.
Students love us — and so will you.
4.9/5
App Store
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 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 THE SCHOOLGPT. 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 THE SCHOOLGPT. 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 Physics: Forces - AQA Combined Science
Maddie
@mads_lh
Forces are everywhere around us - from the weight pulling you down to the friction stopping you from slipping. Understanding how forces work is crucial for explaining everything from why objects fall to how cars brake safely.
Physics - Forces
Vectors and scalars are the foundation of forces. A vector has both size and direction (like velocity and force), whilst a scalar only has size (like speed and mass). Think of vectors as arrows - the longer the arrow, the bigger the magnitude.
Forces are simply pushes or pulls between objects. Contact forces happen when objects touch (like friction when you rub your hands together), while non-contact forces work at a distance (like gravity pulling you towards Earth).
Weight isn't the same as mass - your mass stays constant, but your weight changes depending on the gravitational field strength. On Earth, weight = mass × 9.8 N/kg. The Moon has weaker gravity, so you'd weigh less there but have the same mass.
The resultant force is what you get when you add up all forces acting on an object. If forces balance out , the object either stays still or moves at constant speed. Unbalanced forces cause acceleration in the direction of the resultant force.
💡 Quick Tip: Work done = force × distance. When you push against friction, this energy becomes heat - that's why your hands warm up when you rub them together!
Sign up to see the contentIt's free!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Springs and Motion Basics
Springs demonstrate how objects deform under force. Elastic deformation means the spring bounces back to its original shape - like a rubber band. Plastic deformation means it stays bent permanently, like a paperclip that's been twisted too far.
Hooke's Law shows that extension is directly proportional to applied force: F = k × e . This only works up to the limit of proportionality - push too hard and the spring breaks this rule.
When you stretch a spring, you're storing elastic potential energy. The energy stored equals ½ × k × e². This energy gets released when the spring returns to its original length.
Distance vs displacement and speed vs velocity are crucial distinctions. Distance and speed are scalars (no direction), while displacement and velocity are vectors (include direction). A car going round a roundabout might travel 100m distance but have zero displacement if it ends where it started.
💡 Quick Tip: Typical speeds to remember - walking , cycling , cars , and sound in air . These often appear in exam questions!
Sign up to see the contentIt's free!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Graphs and Newton's Laws
Displacement-time graphs have velocity as their gradient. For curved lines, draw a tangent at any point to find the instantaneous velocity. Velocity-time graphs have acceleration as their gradient, and the area under the line gives you distance travelled.
A steeper gradient means greater acceleration, negative gradients show deceleration, and horizontal lines indicate constant speed. When the line is at zero velocity, the object is stationary.
Newton's First Law explains inertia - objects resist changes to their motion. A book on a table stays put, and a moving car keeps moving unless forces act on them. This is why you lurch forward when a car brakes suddenly.
Newton's Second Law gives us the fundamental equation: F = ma . Doubling the force doubles the acceleration, but doubling the mass halves the acceleration for the same force.
💡 Quick Tip: On velocity-time graphs, count the squares under the line to find distance travelled. Each square represents a specific distance based on the graph's scale.
Sign up to see the contentIt's free!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Newton's Third Law and Vehicle Safety
Newton's Third Law states that every action has an equal and opposite reaction. When you walk, you push backwards on the ground, and the ground pushes you forwards. The forces are equal in size but opposite in direction.
Stopping distances involve two parts: thinking distance (how far you travel while reacting) and braking distance (how far you travel while slowing down). Stopping distance = thinking distance + braking distance.
Thinking distance increases with speed, tiredness, alcohol, drugs, and distractions. Braking distance increases with speed, wet/icy roads, worn tyres, and faulty brakes. Typical reaction times range from 0.2 to 0.9 seconds.
Momentum is always conserved in collisions and explosions. The total momentum before equals the total momentum after, assuming no external forces like friction interfere. This principle explains everything from car crashes to rocket launches.
💡 Quick Tip: Remember that momentum is a vector - direction matters! In head-on collisions, the momentums are in opposite directions, so you subtract rather than add them.
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.
0
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Mock Exam
Quiz
Flashcards
Essay
Most popular content in Physics
Most popular content
English - inspector calls quotes and analysis
Quotes from every main character
English Literature10
Can't find what you're looking for? Explore other subjects.
Students love us — and so will you.
4.9/5
App Store
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 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 THE SCHOOLGPT. 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 THE SCHOOLGPT. 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