Newton's 2nd Law connects force, mass, and acceleration in physics,... Show more
Earth and Space Science
Algebra
Calculus 1
Algebra 1
OverigeSign 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
4
0
haley
11/30/2025
Physics
Physics: Newton's second law
1 / 4
Free Body Diagrams
Free body diagrams help you visualize all forces acting on an object. Each scenario shows different force combinations that determine an object's motion.
For a brick resting on a table, you'd draw two forces: the weight pointing downward and the normal force pointing upward. These forces balance each other perfectly.
When a brick slides at constant speed, the diagram includes four forces: weight downward, normal force upward, applied force in the direction of motion, and friction opposing motion. Since speed is constant, these forces must balance completely.
Think about it: A skydiver reaching terminal velocity experiences balanced forces - gravity pulling down equals air resistance pushing up. That's why they stop accelerating!
For a brick slowing down, the frictional force exceeds the applied force, creating net force opposite to motion. This causes negative acceleration (deceleration).
Applying Newton's 2nd Law
Newton's 2nd Law is expressed as F = ma, where F is force (in Newtons), m is mass (in kilograms), and a is acceleration . This powerful equation lets you calculate any of the three values when you know the other two.
To find acceleration when force and mass are known, rearrange to a = F/m. For example, when a 40 N force acts on a 2.44 kg object, the acceleration is 16.39 m/s².
When calculating force, simply multiply mass by acceleration. A 166 kg object accelerating at 0.1919 m/s² experiences a force of 31.86 N.
Remember: Net force is the combination of all forces acting on an object. When forces act in opposite directions, subtract the smaller from the larger to find net force.
For opposing forces, like when you push with 325 N and a friend pushes back with 190 N, the net force is 135 N. With this net force acting on a 2.5 kg book, the acceleration would be 54 m/s².
Gravity, Air Resistance, and Friction
A falling object experiences gravity's pull, creating a force equal to its mass × gravitational acceleration . For a 14 kg bowling ball, this force is -137.2 N (negative because it points downward).
Air resistance opposes motion through air, acting in the direction opposite to travel. When a falling bowling ball experiences 45 N of air resistance, the net force reduces to -92.2 N, slowing its acceleration.
At terminal velocity, air resistance perfectly balances the weight of the object. For our bowling ball, air resistance would equal 137.2 N upward, resulting in zero net force and constant velocity.
Pro tip: Friction always acts in the direction opposite to motion or potential motion. There's a big difference between static friction (before movement starts) and kinetic friction (during movement).
Friction comes in two types: static friction acts on stationary objects resisting movement, while kinetic friction acts on objects already in motion. Both types depend on the normal force and a coefficient of friction specific to the surfaces in contact.
Friction Problems
The maximum static friction force equals the coefficient of static friction (μs) multiplied by the normal force. For a 4 kg brick on a wooden table , this equals 0.6 × (4 × 9.81) = 23.52 N. That's how much force you need to apply before it starts moving.
Weight affects friction directly. When you stack four identical bricks (16 kg total), the maximum friction force quadruples to 94.08 N because the normal force is four times greater.
For objects already sliding, use the kinetic friction coefficient. A 9 kg rubber block sliding on concrete (μ = 0.65) experiences a friction force of 0.65 × (9 × 9.81) = 57.33 N opposing its motion.
Helpful hint: You can determine an object's normal force by working backward from the friction force when you know the coefficient of friction!
If you need 80 N of force to move an Amazon box with a friction coefficient of 0.20, the normal force must be 400 N. This is found by rearranging the friction equation: normal force = friction force ÷ coefficient of friction.
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.
Most popular content: Newton's Second Law
Most popular content in Physics
Most popular content
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
I think it’s very much worth it and you’ll end up using it a lot once you get the hang of it and even after looking at others notes you can still ask your Artificial intelligence buddy the question and ask to simplify it if you still don’t get it!!! In the end I think it’s worth it 😊👍 ⚠️Also DID I MENTION ITS FREEE YOU DON’T HAVE TO PAY FOR ANYTHING AND STILL GET YOUR GRADES IN PERFECTLY❗️❗️⚠️
Thomas R
iOS user
Knowunity is the BEST app I’ve used in a minute. This is not an ai review or anything this is genuinely coming from a 7th grade student (I know 2011 im young) but dude this app is a 10/10 i have maintained a 3.8 gpa and have plenty of time for gaming. I love it and my mom is just happy I got good grades
Brad T
Android user
Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍
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
I found this app a couple years ago and it has only gotten better since then. I really love it because it can help with written questions and photo questions. Also, it can find study guides that other people have made as well as flashcard sets and practice tests. The free version is also amazing for students who might not be able to afford it. Would 100% recommend
Aubrey
iOS user
Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀
Marco B
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 app is phenomenal down to the correct info and the various topics you can study! I greatly recommend it for people who struggle with procrastination and those who need homework help. It has been perfectly accurate for world 1 history as far as I’ve seen! Geometry too!
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
I think it’s very much worth it and you’ll end up using it a lot once you get the hang of it and even after looking at others notes you can still ask your Artificial intelligence buddy the question and ask to simplify it if you still don’t get it!!! In the end I think it’s worth it 😊👍 ⚠️Also DID I MENTION ITS FREEE YOU DON’T HAVE TO PAY FOR ANYTHING AND STILL GET YOUR GRADES IN PERFECTLY❗️❗️⚠️
Thomas R
iOS user
Knowunity is the BEST app I’ve used in a minute. This is not an ai review or anything this is genuinely coming from a 7th grade student (I know 2011 im young) but dude this app is a 10/10 i have maintained a 3.8 gpa and have plenty of time for gaming. I love it and my mom is just happy I got good grades
Brad T
Android user
Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍
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
I found this app a couple years ago and it has only gotten better since then. I really love it because it can help with written questions and photo questions. Also, it can find study guides that other people have made as well as flashcard sets and practice tests. The free version is also amazing for students who might not be able to afford it. Would 100% recommend
Aubrey
iOS user
Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀
Marco B
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 app is phenomenal down to the correct info and the various topics you can study! I greatly recommend it for people who struggle with procrastination and those who need homework help. It has been perfectly accurate for world 1 history as far as I’ve seen! Geometry too!
Paul T
iOS user
Understanding Newton's Second Law of Motion
Newton's 2nd Law connects force, mass, and acceleration in physics, forming the foundation for understanding how objects move when forces act upon them. This study guide explores free body diagrams and applications of Newton's 2nd Law, including problems involving friction... Show more
Free Body Diagrams
Free body diagrams help you visualize all forces acting on an object. Each scenario shows different force combinations that determine an object's motion.
For a brick resting on a table, you'd draw two forces: the weight pointing downward and the normal force pointing upward. These forces balance each other perfectly.
When a brick slides at constant speed, the diagram includes four forces: weight downward, normal force upward, applied force in the direction of motion, and friction opposing motion. Since speed is constant, these forces must balance completely.
Think about it: A skydiver reaching terminal velocity experiences balanced forces - gravity pulling down equals air resistance pushing up. That's why they stop accelerating!
For a brick slowing down, the frictional force exceeds the applied force, creating net force opposite to motion. This causes negative acceleration (deceleration).
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
Applying Newton's 2nd Law
Newton's 2nd Law is expressed as F = ma, where F is force (in Newtons), m is mass (in kilograms), and a is acceleration . This powerful equation lets you calculate any of the three values when you know the other two.
To find acceleration when force and mass are known, rearrange to a = F/m. For example, when a 40 N force acts on a 2.44 kg object, the acceleration is 16.39 m/s².
When calculating force, simply multiply mass by acceleration. A 166 kg object accelerating at 0.1919 m/s² experiences a force of 31.86 N.
Remember: Net force is the combination of all forces acting on an object. When forces act in opposite directions, subtract the smaller from the larger to find net force.
For opposing forces, like when you push with 325 N and a friend pushes back with 190 N, the net force is 135 N. With this net force acting on a 2.5 kg book, the acceleration would be 54 m/s².
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
Gravity, Air Resistance, and Friction
A falling object experiences gravity's pull, creating a force equal to its mass × gravitational acceleration . For a 14 kg bowling ball, this force is -137.2 N (negative because it points downward).
Air resistance opposes motion through air, acting in the direction opposite to travel. When a falling bowling ball experiences 45 N of air resistance, the net force reduces to -92.2 N, slowing its acceleration.
At terminal velocity, air resistance perfectly balances the weight of the object. For our bowling ball, air resistance would equal 137.2 N upward, resulting in zero net force and constant velocity.
Pro tip: Friction always acts in the direction opposite to motion or potential motion. There's a big difference between static friction (before movement starts) and kinetic friction (during movement).
Friction comes in two types: static friction acts on stationary objects resisting movement, while kinetic friction acts on objects already in motion. Both types depend on the normal force and a coefficient of friction specific to the surfaces in contact.
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
Friction Problems
The maximum static friction force equals the coefficient of static friction (μs) multiplied by the normal force. For a 4 kg brick on a wooden table , this equals 0.6 × (4 × 9.81) = 23.52 N. That's how much force you need to apply before it starts moving.
Weight affects friction directly. When you stack four identical bricks (16 kg total), the maximum friction force quadruples to 94.08 N because the normal force is four times greater.
For objects already sliding, use the kinetic friction coefficient. A 9 kg rubber block sliding on concrete (μ = 0.65) experiences a friction force of 0.65 × (9 × 9.81) = 57.33 N opposing its motion.
Helpful hint: You can determine an object's normal force by working backward from the friction force when you know the coefficient of friction!
If you need 80 N of force to move an Amazon box with a friction coefficient of 0.20, the normal force must be 400 N. This is found by rearranging the friction equation: normal force = friction force ÷ coefficient of friction.
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.
4
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Mock Exam
Quiz
Flashcards
Essay
Similar Content
Dynamics and Forces
Explore the fundamental concepts of dynamics, including weight, mass, gravity, acceleration, and Newton's laws of motion. This summary covers key topics such as terminal velocity, speed calculations, and the relationship between force and mass. Ideal for students preparing for exams or seeking to understand the principles of motion and forces.
PhysicsS3
Distance and Displacement
Notes on the differences between distance and displacement, including definitions of position, distance, and displacement, explanations of how to use cardinal directions in physics, vector vs. scalar, and word problem examples.
Physicsintro to kinematics
kinematic terms in physics
Physics10th
Acceleration
Definition and examples
Physics2D kinematics notes
2 dimension kinematics in physics
Physics10th
Physics: Forces
- Applied Force - Normal Force - Frictional Force - Tension Force - Free body diagrams - Force & Newton's second law
PhysicsMost popular content: Newton's Second Law
Most popular content in Physics
Most popular content
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
I think it’s very much worth it and you’ll end up using it a lot once you get the hang of it and even after looking at others notes you can still ask your Artificial intelligence buddy the question and ask to simplify it if you still don’t get it!!! In the end I think it’s worth it 😊👍 ⚠️Also DID I MENTION ITS FREEE YOU DON’T HAVE TO PAY FOR ANYTHING AND STILL GET YOUR GRADES IN PERFECTLY❗️❗️⚠️
Thomas R
iOS user
Knowunity is the BEST app I’ve used in a minute. This is not an ai review or anything this is genuinely coming from a 7th grade student (I know 2011 im young) but dude this app is a 10/10 i have maintained a 3.8 gpa and have plenty of time for gaming. I love it and my mom is just happy I got good grades
Brad T
Android user
Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍
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
I found this app a couple years ago and it has only gotten better since then. I really love it because it can help with written questions and photo questions. Also, it can find study guides that other people have made as well as flashcard sets and practice tests. The free version is also amazing for students who might not be able to afford it. Would 100% recommend
Aubrey
iOS user
Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀
Marco B
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 app is phenomenal down to the correct info and the various topics you can study! I greatly recommend it for people who struggle with procrastination and those who need homework help. It has been perfectly accurate for world 1 history as far as I’ve seen! Geometry too!
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
I think it’s very much worth it and you’ll end up using it a lot once you get the hang of it and even after looking at others notes you can still ask your Artificial intelligence buddy the question and ask to simplify it if you still don’t get it!!! In the end I think it’s worth it 😊👍 ⚠️Also DID I MENTION ITS FREEE YOU DON’T HAVE TO PAY FOR ANYTHING AND STILL GET YOUR GRADES IN PERFECTLY❗️❗️⚠️
Thomas R
iOS user
Knowunity is the BEST app I’ve used in a minute. This is not an ai review or anything this is genuinely coming from a 7th grade student (I know 2011 im young) but dude this app is a 10/10 i have maintained a 3.8 gpa and have plenty of time for gaming. I love it and my mom is just happy I got good grades
Brad T
Android user
Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍
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
I found this app a couple years ago and it has only gotten better since then. I really love it because it can help with written questions and photo questions. Also, it can find study guides that other people have made as well as flashcard sets and practice tests. The free version is also amazing for students who might not be able to afford it. Would 100% recommend
Aubrey
iOS user
Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀
Marco B
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 app is phenomenal down to the correct info and the various topics you can study! I greatly recommend it for people who struggle with procrastination and those who need homework help. It has been perfectly accurate for world 1 history as far as I’ve seen! Geometry too!
Paul T
iOS user