物理でよく出てくる「力の合成と分解」について学ぼう。複数の力を1つにまとめたり、1つの力を複数に分けたりする方法で、物体の運動を理解するのに超重要な基本技術だ。
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力の合成と分解の基礎
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力の合成と分解の基本概念
物理の問題を解くとき、複数の力が同時に働いていると複雑で分かりにくいよね。そんなときに使うのが力の合成と分解という技術だ。
**合力（ごうりょく）**は、複数の力をまとめて1つの力にしたもの。元の複数の力と全く同じ効果を持つ。**分力（ぶんりょく）**は逆に、1つの力を複数の力に分けたもので、すべて合わせると元の力と同じ効果になる。
力は矢印で表現する。矢印の向きが力の方向、長さが力の大きさを表すんだ。矢印の始まる点を作用点と呼ぶから覚えておこう。
重要ポイント: 力の平行四辺形の法則は、2つの力を2辺とする平行四辺形を描いて、その対角線が合力になるという基本ルールだ。
力の合成のやり方
力の合成は力の向きによって方法が変わる。まずは簡単なパターンから見ていこう。
同じ向きの力なら、単純に足し算するだけ。右向き3Nと5Nなら、合力は右向き8Nだ。反対向きの力は、大きい方から小さい方を引き算して、向きは大きい方と同じになる。
角度がある2つの力が一番重要で、ここで平行四辺形の法則を使う。2つの力の矢印を作用点で合わせて描き、それぞれの先からもう一方と平行な線を引く。できた平行四辺形の対角線が合力になるんだ。
コツ: 作図では必ず定規と分度器を使おう。フリーハンドだと正確な答えが出ないし、テストで減点される可能性が高い。
力の分解と実際の計算例
力の分解は合成の逆操作で、1つの力を指定された2つの方向に分ける作業だ。特に斜面の問題でよく使われる。
例えば質量6kgの物体の重力60Nを考えてみよう。この重力を斜面に平行な力と垂直な力に分解すると、物体がなぜ滑り落ちるかが分かる。平行な分力が物体を下向きに押し、垂直な分力が斜面に押し付ける力になる。
作図の手順は、まず分解したい力を描き、作用点から2つの方向へ直線を引く。力の終点からそれぞれの直線に平行な線を引いて、作用点との交点までが分力になる。
テストの注意点: 重力は必ず真下向き！斜面に対して垂直に描いてしまうミスが多いから気をつけよう。
作図練習と具体例
60°の角度で4Nずつの力が働く場合を実際に作図してみよう。方眼紙で1N=1cmとして、正確に角度を測って矢印を描く。
平行四辺形を完成させると、この場合はひし形になる。対角線の長さを測ると約6.9cmになるので、合力は約6.9Nだ。数学の知識も活用して、120°の二等辺三角形として計算で確認できる。
作図では三角定規を2つ使うと平行な線が正確に描けるよ。始点と終点を間違えないよう、合成では2つの力の作用点を合わせ、分解では元の力の終点から補助線を引くのがポイント。
実用的なコツ: 定規、分度器、三角定規をセットで使えば、テストでも確実に正解できる。道具の使い方を普段から練習しておこう。
斜面問題での力の分解
斜面上の物体は物理でよく出る重要なパターンだ。質量6kg（重力60N）の台車が斜面にある場合を考えてみよう。
重力を斜面に平行な分力F_Aと斜面に垂直な分力F_Bに分解する。F_Aが物体を滑らせようとする力で、F_Bが物体を斜面に押し付ける力になる。この分解によって、物体の運動が力の成分で説明できるようになるんだ。
作図では重力の矢印を真下向きに描き、その終点から斜面に平行・垂直な方向への垂線を引く。重力の作用点から垂線との交点まで引いた矢印が分力だ。
理解のポイント: この分解により、なぜ斜面の角度が急になると物体が滑りやすくなるのかが、数値で説明できるようになる。
テストで気をつけるポイント
作図問題では丁寧さが命。フリーハンドは絶対にダメで、必ず定規を使おう。平行な線は三角定規を2つ使うと正確に描ける。
力の矢印の始点と終点を正確に。合成では2つの力の始点（作用点）を合わせ、分解では元の力の終点から補助線を引くのを忘れずに。始点から引くと間違いの元だ。
重力の向きは常に真下。斜面に対して垂直に描いてしまうミスが本当に多いから注意しよう。また、合力とつり合いを混同しないこと。合力は複数の力をまとめたもので、つり合いは合力がゼロの状態だ。
最終チェック: 答案では矢印の向きと長さが正確か、計算結果と作図結果が一致しているかを必ず確認しよう。
重要事項の総まとめ
力の合成は複数の力を1つにまとめて合力を求めること。力の分解は1つの力を複数に分けて分力を求めることだ。
角度のある2力の合成・分解には平行四辺形の法則を使う。合成では2力を2辺として平行四辺形を描き対角線が合力、分解では1力を対角線として平行四辺形を描き2辺が分力になる。
作図の手順をしっかり覚えて、斜面上の物体にはたらく重力は「平行」と「垂直」な力に分解するのが基本パターンだ。この基礎をマスターすれば、物理の力学問題がぐっと解きやすくなるよ。
合格への道: この単元は物理の基礎中の基礎。ここを完璧にすれば、後の運動方程式や エネルギーの問題も楽に解けるようになる。
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 in 物理
Can't find what you're looking for? Explore other subjects.
Students love us — and so will you.
4.6/5
App Store
4.7/5
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 Knowunity AI. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This 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 Knowunity AI. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This 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
力の合成と分解の基礎
物理でよく出てくる「力の合成と分解」について学ぼう。複数の力を1つにまとめたり、1つの力を複数に分けたりする方法で、物体の運動を理解するのに超重要な基本技術だ。
力の合成と分解の基本概念
物理の問題を解くとき、複数の力が同時に働いていると複雑で分かりにくいよね。そんなときに使うのが力の合成と分解という技術だ。
**合力（ごうりょく）**は、複数の力をまとめて1つの力にしたもの。元の複数の力と全く同じ効果を持つ。**分力（ぶんりょく）**は逆に、1つの力を複数の力に分けたもので、すべて合わせると元の力と同じ効果になる。
力は矢印で表現する。矢印の向きが力の方向、長さが力の大きさを表すんだ。矢印の始まる点を作用点と呼ぶから覚えておこう。
重要ポイント: 力の平行四辺形の法則は、2つの力を2辺とする平行四辺形を描いて、その対角線が合力になるという基本ルールだ。
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力の合成のやり方
力の合成は力の向きによって方法が変わる。まずは簡単なパターンから見ていこう。
同じ向きの力なら、単純に足し算するだけ。右向き3Nと5Nなら、合力は右向き8Nだ。反対向きの力は、大きい方から小さい方を引き算して、向きは大きい方と同じになる。
角度がある2つの力が一番重要で、ここで平行四辺形の法則を使う。2つの力の矢印を作用点で合わせて描き、それぞれの先からもう一方と平行な線を引く。できた平行四辺形の対角線が合力になるんだ。
コツ: 作図では必ず定規と分度器を使おう。フリーハンドだと正確な答えが出ないし、テストで減点される可能性が高い。
Sign up to see the contentIt's free!
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力の分解と実際の計算例
力の分解は合成の逆操作で、1つの力を指定された2つの方向に分ける作業だ。特に斜面の問題でよく使われる。
例えば質量6kgの物体の重力60Nを考えてみよう。この重力を斜面に平行な力と垂直な力に分解すると、物体がなぜ滑り落ちるかが分かる。平行な分力が物体を下向きに押し、垂直な分力が斜面に押し付ける力になる。
作図の手順は、まず分解したい力を描き、作用点から2つの方向へ直線を引く。力の終点からそれぞれの直線に平行な線を引いて、作用点との交点までが分力になる。
テストの注意点: 重力は必ず真下向き！斜面に対して垂直に描いてしまうミスが多いから気をつけよう。
Sign up to see the contentIt's free!
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作図練習と具体例
60°の角度で4Nずつの力が働く場合を実際に作図してみよう。方眼紙で1N=1cmとして、正確に角度を測って矢印を描く。
平行四辺形を完成させると、この場合はひし形になる。対角線の長さを測ると約6.9cmになるので、合力は約6.9Nだ。数学の知識も活用して、120°の二等辺三角形として計算で確認できる。
作図では三角定規を2つ使うと平行な線が正確に描けるよ。始点と終点を間違えないよう、合成では2つの力の作用点を合わせ、分解では元の力の終点から補助線を引くのがポイント。
実用的なコツ: 定規、分度器、三角定規をセットで使えば、テストでも確実に正解できる。道具の使い方を普段から練習しておこう。
Sign up to see the contentIt's free!
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斜面問題での力の分解
斜面上の物体は物理でよく出る重要なパターンだ。質量6kg（重力60N）の台車が斜面にある場合を考えてみよう。
重力を斜面に平行な分力F_Aと斜面に垂直な分力F_Bに分解する。F_Aが物体を滑らせようとする力で、F_Bが物体を斜面に押し付ける力になる。この分解によって、物体の運動が力の成分で説明できるようになるんだ。
作図では重力の矢印を真下向きに描き、その終点から斜面に平行・垂直な方向への垂線を引く。重力の作用点から垂線との交点まで引いた矢印が分力だ。
理解のポイント: この分解により、なぜ斜面の角度が急になると物体が滑りやすくなるのかが、数値で説明できるようになる。
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テストで気をつけるポイント
作図問題では丁寧さが命。フリーハンドは絶対にダメで、必ず定規を使おう。平行な線は三角定規を2つ使うと正確に描ける。
力の矢印の始点と終点を正確に。合成では2つの力の始点（作用点）を合わせ、分解では元の力の終点から補助線を引くのを忘れずに。始点から引くと間違いの元だ。
重力の向きは常に真下。斜面に対して垂直に描いてしまうミスが本当に多いから注意しよう。また、合力とつり合いを混同しないこと。合力は複数の力をまとめたもので、つり合いは合力がゼロの状態だ。
最終チェック: 答案では矢印の向きと長さが正確か、計算結果と作図結果が一致しているかを必ず確認しよう。
Sign up to see the contentIt's free!
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重要事項の総まとめ
力の合成は複数の力を1つにまとめて合力を求めること。力の分解は1つの力を複数に分けて分力を求めることだ。
角度のある2力の合成・分解には平行四辺形の法則を使う。合成では2力を2辺として平行四辺形を描き対角線が合力、分解では1力を対角線として平行四辺形を描き2辺が分力になる。
作図の手順をしっかり覚えて、斜面上の物体にはたらく重力は「平行」と「垂直」な力に分解するのが基本パターンだ。この基礎をマスターすれば、物理の力学問題がぐっと解きやすくなるよ。
合格への道: この単元は物理の基礎中の基礎。ここを完璧にすれば、後の運動方程式や エネルギーの問題も楽に解けるようになる。
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.
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Students love us — and so will you.
4.6/5
App Store
4.7/5
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 Knowunity AI. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This 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 Knowunity AI. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This 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