Forces (continued)
Overview
Push a door near its handle and it swings open easily; push near the hinge and it barely moves. That everyday difference is the turning effect of a force, or moment, and it explains spanners, see-saws, cranes and why a wide base stops you toppling over.
In this lesson you will meet friction and drag, define and calculate the moment of a force, apply the principle of moments to balance a beam, and use the centre of gravity to judge whether an object is stable. These ideas turn into reliable marks once you practise the calculations.
Objectives
- Describe solid friction as the force between two surfaces that may impede motion and produce heating
- Know that friction (drag) acts on an object moving through a liquid
- Know that friction (drag) acts on an object moving through a gas (e.g. air resistance)
- Describe the moment of a force as a measure of its turning effect and give everyday examples
- Define the moment of a force as moment = force × perpendicular distance from the pivot; recall and use this equation
- Apply the principle of moments to situations with one force each side of the pivot, including balancing of a beam
- State that, when there is no resultant force and no resultant moment, an object is in equilibrium
- State what is meant by centre of gravity
- Describe an experiment to determine the position of the centre of gravity of an irregularly shaped plane lamina
- Describe, qualitatively, the effect of the position of the centre of gravity on the stability of simple objects
- [Supplement] Apply the principle of moments to other situations, including those with more than one force each side of the pivot
- [Supplement] Describe an experiment to demonstrate that there is no resultant moment on an object in equilibrium
Audio Lesson
Listen to this lesson in the app
Mind map
This topic is mapped out so you can see how the ideas connect.
Open the mind map in the app
Flashcards
Quick recall practice on the facts this topic is tested on.
Practise these cards in the app
Lesson Note
Complete Note Available on the Green Bridge App
Get the Green Bridge CBT app on your phone or computer for the complete IGCSE library: past papers, mark schemes, mind maps, flashcards and audio lessons.
Lesson Evaluation
Congratulations on completing the lesson on Forces (continued). Now that youve explored the key concepts and ideas, its time to put your knowledge to the test. This section offers a variety of practice questions designed to reinforce your understanding and help you gauge your grasp of the material.
You will encounter a mix of question types, including multiple-choice questions, short answer questions, and essay questions. Each question is thoughtfully crafted to assess different aspects of your knowledge and critical thinking skills.
Use this evaluation section as an opportunity to reinforce your understanding of the topic and to identify any areas where you may need additional study. Don't be discouraged by any challenges you encounter; instead, view them as opportunities for growth and improvement.
- The moment of a force is calculated using: A. force / distance B. force x perpendicular distance C. force + distance D. force x time Answer: B
- A force of 25 N acts 0.40 m from a pivot. The moment is: A. 0.016 N m B. 10 N m C. 62.5 N m D. 25.4 N m Answer: B
- An object is in equilibrium when: A. it is moving fast B. there is no resultant force and no resultant moment C. only the forces balance D. only the moments balance Answer: B
- An object is most stable when it has: A. a high centre of gravity and narrow base B. a low centre of gravity and wide base C. a high centre of gravity and wide base D. a low centre of gravity and narrow base Answer: B
- Drag on a moving object: A. is constant at all speeds B. increases as speed increases C. acts in the direction of motion D. only acts in liquids Answer: B
Work through these questions in the app
Work through these questions in the app
Recommended Books
Further learning from open sources
-
Textbook section
Stability
It is one thing to have a system in equilibrium; it is quite another for it to be stable. The toy doll perched on the man’s hand in Figure 9.9 , for example, is not in stable equilibrium. There are three types of equilibrium : stable , unstable , and neutral . Figures throughout this module illustra
"College Physics: Stability" by OpenStax, OpenStax, Rice University, licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Source: https://openstax.org/books/college-physics/pages/9-3-stability. Access for free at https://openstax.org/books/college-physics/pages/1-introduction
-
Textbook section
Drag Forces
Another interesting force in everyday life is the force of drag on an object when it is moving in a fluid (either a gas or a liquid). You feel the drag force when you move your hand through water. You might also feel it if you move your hand during a strong wind. The faster you move your hand, the h
"College Physics: Drag Forces" by OpenStax, OpenStax, Rice University, licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Source: https://openstax.org/books/college-physics/pages/5-2-drag-forces. Access for free at https://openstax.org/books/college-physics/pages/1-introduction
Published by other organisations under open licences, credited as they ask. Links open their websites.
Practice Mock Questions
Want to practice mock questions on Forces (continued)? Download the Green Bridge CBT app to access mock questions and full practice assessments for this topic.
Download The App On Google Playstore
Everything you need to excel in your exams
