Gravity, forces, and motion are the foundation of physics that... Show more
Physics
Algebra
Overige
Algebra 1Sign 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
9
•
Dec 21, 2025
•
Understanding Gravitational Acceleration and Newton's Laws
Smriti Naresh
@doctor_smriti_4_life
1 / 5
Gravitational Acceleration & Force
When you drop your phone (accidentally, of course!), it accelerates toward the ground at approximately -10 m/s² on Earth. This means every second it falls, it gains 10 m/s of speed. But drop that same phone on the moon, and it would accelerate much slower, at only -1.625 m/s².
This difference happens because the force of gravity varies depending on where you are in the universe. We calculate this force using the equation Fg = mg, where Fg is the weight (measured in Newtons), m is mass (measured in kilograms), and g is the gravitational acceleration.
An important distinction in physics: mass and weight are different things! Your mass stays the same whether you're on Earth or the Moon, but your weight changes because the gravitational acceleration is different.
Physics Fun Fact: If you weigh 600 Newtons on Earth (about 135 pounds), you'd only weigh about 98 Newtons on the Moon. You could jump six times higher there!
Forces and Free Body Diagrams
Forces are pushes or pulls that can make objects move when unbalanced. They come in two main categories: contact forces and field forces.
Contact forces require physical touching to work. These include applied force (when you push something), tension force (pulling with a rope), friction force (resisting motion), normal force (surfaces pushing back), and spring force. Think about trying to move a heavy box—you need to touch it!
Field forces work without contact. Gravity is the most familiar—it pulls you down even when you're jumping and not touching the ground. Magnetic and electrical forces also work through fields.
The normal force is what a surface exerts on an object sitting on it. It's called "normal" because it acts perpendicular to the surface. When you stand on the floor, it pushes back against you with exactly the force needed to keep you from falling through.
Think about it: When you're sitting in your chair right now, the normal force is pushing up on you with exactly the same strength that gravity is pulling down on you. That's why you don't sink through the chair!
Tension and Free Body Diagrams
Tension force is what a rope, string, or cord applies when it pulls on an object. What makes tension special is that it can only pull, never push—try pushing something with a rope and you'll see it just goes slack!
Free Body Diagrams (FBDs) are simple but powerful visual tools that show all the forces acting on an object. In these diagrams, we represent the object as a dot or box, with arrows showing the direction and relative strength of each force.
Different situations create different force patterns. A box sitting on a flat surface has just two forces: gravity pulling down and normal force pushing up. A free-falling object experiences only gravity. When someone pushes a box across a rough floor, we see normal force, gravity, friction, and the pushing force all at once.
Pro Tip: When drawing Free Body Diagrams, start by identifying if the object is moving or stationary, then figure out what forces could be causing that state. The diagram should tell the complete force "story" of the object.
Newton's Laws
Newton's First Law (Law of Inertia) states that objects keep doing what they're doing unless acted upon by an unbalanced force. If something's moving, it keeps moving; if it's still, it stays still. This resistance to change is called inertia—like when you slide across the floor in socks and can't easily stop.
Forces can be balanced (equal in opposite directions, causing no motion) or unbalanced (causing motion). Imagine two people pushing equally on opposite sides of a door versus one person pushing harder than the other.
Newton's Second Law gives us the formula ΣF = ma, which can be rearranged to a = ΣF/m. This means an object's acceleration equals the net force applied divided by its mass. The heavier something is, the more force needed to accelerate it. The Σ (sigma) symbol means "sum" or "net"—we add forces in the same direction and subtract opposing ones.
Real World Application: This is why your car accelerates faster when it's just you versus when it's full of friends and luggage! The same engine force has to move more mass, resulting in less acceleration.
Newton's Third Law & Practice Problems
Newton's Third Law states that for every force, there is an equal and opposite force acting on the other object. These paired forces are called "third law pairs." When you push against a wall, the wall pushes back on you with equal strength—which is why your hand feels pressure!
This law applies everywhere: The Earth pulls on the Moon with the same force that the Moon pulls on Earth. Even though the effects look different (due to their mass difference), the forces are identical.
Let's see these concepts in practice problems:
Problem 1: A car accelerates at 2m/s² for 5 seconds from rest. To find distance traveled:
- First find final velocity: v = a × t = 2m/s² × 5s = 10m/s
- Then calculate distance: d = average velocity × time = 10m/s × 5s ÷ 2 = 25m
Problem 2: A ball thrown upward at 15m/s reaches its highest point when:
- At highest point, final velocity = 0 m/s
- Using t = Δv ÷ a = 15m/s ÷ 9.8m/s² = 1.53 seconds
Study Tip: For problems like these, always identify what you know, what you need to find, and which equation connects them. Start with the simplest formula first!
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 Laws of Motion
Most popular content in AP Physics 1
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 Gravitational Acceleration and Newton's Laws
Smriti Naresh
@doctor_smriti_4_life
Gravity, forces, and motion are the foundation of physics that explain how everything moves around us. These concepts help us understand why objects fall, why we feel "heavy" on Earth but would feel "lighter" on the Moon, and how objects... Show more
Gravitational Acceleration & Force
When you drop your phone (accidentally, of course!), it accelerates toward the ground at approximately -10 m/s² on Earth. This means every second it falls, it gains 10 m/s of speed. But drop that same phone on the moon, and it would accelerate much slower, at only -1.625 m/s².
This difference happens because the force of gravity varies depending on where you are in the universe. We calculate this force using the equation Fg = mg, where Fg is the weight (measured in Newtons), m is mass (measured in kilograms), and g is the gravitational acceleration.
An important distinction in physics: mass and weight are different things! Your mass stays the same whether you're on Earth or the Moon, but your weight changes because the gravitational acceleration is different.
Physics Fun Fact: If you weigh 600 Newtons on Earth (about 135 pounds), you'd only weigh about 98 Newtons on the Moon. You could jump six times higher there!
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
Forces and Free Body Diagrams
Forces are pushes or pulls that can make objects move when unbalanced. They come in two main categories: contact forces and field forces.
Contact forces require physical touching to work. These include applied force (when you push something), tension force (pulling with a rope), friction force (resisting motion), normal force (surfaces pushing back), and spring force. Think about trying to move a heavy box—you need to touch it!
Field forces work without contact. Gravity is the most familiar—it pulls you down even when you're jumping and not touching the ground. Magnetic and electrical forces also work through fields.
The normal force is what a surface exerts on an object sitting on it. It's called "normal" because it acts perpendicular to the surface. When you stand on the floor, it pushes back against you with exactly the force needed to keep you from falling through.
Think about it: When you're sitting in your chair right now, the normal force is pushing up on you with exactly the same strength that gravity is pulling down on you. That's why you don't sink through the chair!
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
Tension and Free Body Diagrams
Tension force is what a rope, string, or cord applies when it pulls on an object. What makes tension special is that it can only pull, never push—try pushing something with a rope and you'll see it just goes slack!
Free Body Diagrams (FBDs) are simple but powerful visual tools that show all the forces acting on an object. In these diagrams, we represent the object as a dot or box, with arrows showing the direction and relative strength of each force.
Different situations create different force patterns. A box sitting on a flat surface has just two forces: gravity pulling down and normal force pushing up. A free-falling object experiences only gravity. When someone pushes a box across a rough floor, we see normal force, gravity, friction, and the pushing force all at once.
Pro Tip: When drawing Free Body Diagrams, start by identifying if the object is moving or stationary, then figure out what forces could be causing that state. The diagram should tell the complete force "story" of the object.
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 Laws
Newton's First Law (Law of Inertia) states that objects keep doing what they're doing unless acted upon by an unbalanced force. If something's moving, it keeps moving; if it's still, it stays still. This resistance to change is called inertia—like when you slide across the floor in socks and can't easily stop.
Forces can be balanced (equal in opposite directions, causing no motion) or unbalanced (causing motion). Imagine two people pushing equally on opposite sides of a door versus one person pushing harder than the other.
Newton's Second Law gives us the formula ΣF = ma, which can be rearranged to a = ΣF/m. This means an object's acceleration equals the net force applied divided by its mass. The heavier something is, the more force needed to accelerate it. The Σ (sigma) symbol means "sum" or "net"—we add forces in the same direction and subtract opposing ones.
Real World Application: This is why your car accelerates faster when it's just you versus when it's full of friends and luggage! The same engine force has to move more mass, resulting in less acceleration.
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 & Practice Problems
Newton's Third Law states that for every force, there is an equal and opposite force acting on the other object. These paired forces are called "third law pairs." When you push against a wall, the wall pushes back on you with equal strength—which is why your hand feels pressure!
This law applies everywhere: The Earth pulls on the Moon with the same force that the Moon pulls on Earth. Even though the effects look different (due to their mass difference), the forces are identical.
Let's see these concepts in practice problems:
Problem 1: A car accelerates at 2m/s² for 5 seconds from rest. To find distance traveled:
- First find final velocity: v = a × t = 2m/s² × 5s = 10m/s
- Then calculate distance: d = average velocity × time = 10m/s × 5s ÷ 2 = 25m
Problem 2: A ball thrown upward at 15m/s reaches its highest point when:
- At highest point, final velocity = 0 m/s
- Using t = Δv ÷ a = 15m/s ÷ 9.8m/s² = 1.53 seconds
Study Tip: For problems like these, always identify what you know, what you need to find, and which equation connects them. Start with the simplest formula first!
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.
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: Newton's Laws of Motion
Most popular content in AP Physics 1
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