Force – Contact and Non-contact 11 September 2021 09:59 1. Force Force can be defined as a push or a pull. To be more scientific, we can say force is that which tries to overcome the inertia of an object. Inertia: Tendency of an object at rest to remain at rest and tendency of an object in motion to continue to be in motion. 2. Effect of force: Force can change the: a. Shape and size of an object b. Speed of an object c. Direction at which an object is moving. Remember, force will always try to do one of the above but it may not always succeed. For example, if you push a mountain the mountain does not move. It is not because force is not being applied but rather the force applied by you is very less for the mountain to move. 3. Force always act in pairs Example 1, In the above example, we see that the book applies a force on the table (its weight) and the table applied an equal and opposite force on the book (reaction force) Example 2, In the above example, the earth applies a force on the apple (gravity of earth on apple) and the apple also applies a force on the earth (gravity of apple on earth). I know it is difficult to comprehend because we have never seen the earth moving towards the apple but always seen the apple fall towards the earth. Do not be confused it is not because the apple is not pulling the earth but because its pulling force is too less to move the earth (Similar to you trying to move a mountain) Also note, if the earth pulls the apple with 2 N then the apple also pulls the earth with 2 N 4. Contant and Non-contact forces Contact forces occur when objects are touching each other. Non-contact forces occur both when the objects are touching and when they are not touching each other. Examples of contact force: friction, normal reaction force, air resistance, water resistance, upthrust, etc. Examples of non-contact force: electrostatic force, magnetic force and gravitational force Some properties of non-contact force: a. Electrostatic and magnetic are both attractive as well as repulsive but gravitational force is only attractive in nature. b. In the case of all three non-contact forces, the farther the objects are the lesser is the force. 5. PowerPoint used in class: <<Type of Force_8.ppt>> <<KS3 Forces L1 Contact and Non Contact Forces PowerPoint.pptx>> 6. Video Links: a. What is Force? | Force and Pressure | Physics | Don't Memorise b. What are CONTACT Forces? - Part 1 | Physics | Don't Memorise c. What are CONTACT Forces? - Part 2 | Physics | Don't Memorise d. What are NON-CONTACT Forces? - Part 1 | Physics | Don't Memorise e. What are NON-CONTACT Forces? - Part 2 | Physics | Don't Memorise 7. Solved worksheet This worksheet was solved in the class. If you have not done it then attempt the questions before going through the answer key <<Investigating Forces Results Table LA.pdf>> Balanced and Unbalanced Forces 11 September 2021 10:26 1. Remember in the last topic - Force we learned three effects of Force. Force can change the: 1. Shape and size of an object 2. Speed of an object 3. Direction at which an object is moving. These effects are seen only when an object experiences unbalanced force and never when an object experiences balanced force. Now you may wonder what balanced and unbalanced forces are. Let's learn about them. 2. Balanced Forces: Balanced forces are forces that are act in equal size and opposite direction on an object. In the above example we can see from the force arrows that the force acting on the pineapple is equal and opposite. So we can say that the pineapple is being acted by balanced force. Hence, this force cannot change the shape of the pineapple, direction of the pineapple nor the speed of the pineapple. The last point needs more clarity. When we say balanced forces cannot change the speed of the pineapple we mean to say that if it is at rest then it will remain at rest. If it is moving then it will move with constant velocity. (no change in speed or direction) The above is also an example of balanced forces as you can see from the force arrows (they are equal in size and opposite to each other). This does not mean that the parachutist is at rest as in the case of the pineapple above but that the parachutist is moving with constant speed downwards. Unbalanced force When forces acting on an object is not equal to each other then the object experiences unbalanced force. In the above case of a falling feather, we can see that the downward force arrow is more than the upward force arrow. Hence weight is more than air resistance. This feather is falling down with acceleration; with increasing speed. In the above example, we see that the forces acting up and down are balanced. Hence these forces do not affect the child and the sledge in any way. But the forwards force is more than the backwards force. These forces are unbalanced and hence the sledge moves forwards with increasing speed. In the above example, we see that the upwards force of air resistance is more than the downward force of weight. These forces are unbalanced. Students often mistake this as the parachute moving upwards. That is incorrect because the parachute always move down. The unbalanced forces are causing the parachute to slow down while falling. For a falling object: If the forces are balanced then the object is falling with constant velocity. If the forces are unbalanced and the downwards force is more, then the object is falling with increasing speed. If the forces are unbalanced and the upwards force is more, then the object is falling with decreasing speed. PowerPoint for self-study: <<Forces L2 Measuring Forces PowerPoint.pptx>> 5. Video links: Balanced & Unbalanced Forces | Forces & Motion | Physics | FuseSchool FLYING PHONE SCAM EXPOSED (so I built a REAL one) 6. Balanced and Unbalanced Forces-Explanation and Real-Life Examples 7. Playlist for more: https://youtube.com/playlist?list=PLurjkZV1ykGZlx51bTBiw7X_908PRzgMe 8. Measurement of Force: Force is measured by a newton meter. It is measured in newtons. The symbol of newton is N. Remember when we write units in full form we always start with small letter. When we write symbols we starts with capital only if the unit is named after a person. Newton meter 9. Solved worksheet: <<Forces L2 Measuring Forces Worksheet HA.pdf>> 10. Interactive simulation: https://www.physicsclassroom.com/Physics-Interactives/Newtons-Laws/RocketSledder/Rocket-Sledder-Interactive https://phet.colorado.edu/en/simulations/forces-and-motion-basics 11. Simulation to draw force diagrams: https://www.physicsclassroom.com/Physics-Interactives/Newtons-Laws/Free-BodyDiagrams/Free-Body-Diagram-Interactive 12. Worksheets Balanced and Unbalanced Forces/ Speed, Velocity, and Acceleration 13. For the ones who need something extra to push their limits: https://www.generationgenius.com/?share=E7FDE Air Resistance Saturday, September 11, 2021 11:12 AM 1. Air resistance is a drag force that slows down objects moving through air. Drag force is any force that resists motion. 2. Misconception It is commonly believed by people that heavy objects fall faster than lighter objects. Galileo proved it to be wrong with an experiment. He proved that both heavy and light objects fall at the same rate. This does not mean that the force of gravity on both of them is same because force of gravity is more on heavier objects. It only means that the acceleration (change in velocity with time) produced in objects do not depend on their mass. Hence, even if an elephant and a man jump into a swimming pool from a height they will land at the same time. People often used the case of a feather or balloon to state that lighter objects fall slower than heavier objects. They were ignorant of air resistance. It is not that the lighter object is falling slower but that air was stopping it from falling at the same rate as a heavy object. Brian Cox visits the world's biggest vacuum | Human Universe - BBC Brainiac - Do heavy objects fall faster than light objects ? Aristotle vs Galileo Misconceptions About Falling Objects 3. PowerPoint for self-study <<Forces L4 Air Resistance PowerPoint.pptx>> 4. Investigation – Air resistance <<Investigating Air Resistance Worksheet HA.pdf>> <<Investigating Parachute Method Worksheet.pdf>> 5. Advantages of air resistance: It causes meteors to burn away. Without air resistance we would have never existed on the planet. The huge craters on moon would have been the face of the earth too. It allows for the operation of parachutes. Without air resistance parachutes, gliders would not have worked. Disadvantages of air resistance: It slows down moving objects which leads to huge energy losses. A company is working to remove air resistance to improve travel time: Hyperloop Explained Friction Saturday, September 11, 2021 11:32 AM 1. Friction Definition: Friction is the force that resists relative motion between objects. 2. Friction does not act on an object which is at rest on a flat surface and is not acted by any external push or pull. It only starts acting when an object moves or even tries to move. 3. Types of friction: a. Static friction: This friction acts when a force tries to move an object but it does not move. For example, when you try to push a heavy bed which does not move it is because of static friction. b. Sliding friction: This friction acts when force applied on an object makes it slide over a surface. c. Rolling friction: This friction acts when force applied on an object makes the object roll over something such as wheels. For example, when you push your trolley bag there is rolling friction acting on the wheels of the trolley. d. Fluid friction: Friction that acts on an object which moves in a fluid. Example, air resistance and water resistance. Video to understand: Types of frictional forces with examples Friction - Why is it difficult to pull a boat on the beach than on the sea? | #aumsum #kids #science c. PowerPoint: <<Resistive Forces Friction PowerPoint.pptx>> 4. Investigating air resistance: Do the investigation on a simulation software. Details are mentioned in the document and then complete the worksheet. Answer to the worksheet is given at the end but do not go through it until you attempt the worksheet. <<Investigating Friction.docx>> <<Friction Investigation Method 2 Worksheet HA Eco B&W.pdf>> 5. Reason for friction: Friction comes into play due to the interaction between the molecules in contact with each other. Example, a rubber eraser placed on glass encounters a lot of friction. This is because the molecules of rubber is attracted to the molecules of glass which causes friction when rubber eraser tries to move over the glass. Often rough surfaces offer greater friction due to the nature of molecules of interacting objects but there are soft surfaces that can offer an even greater friction when other soft material come into contact with it. 6. Friction – A necessary evil We cannot live without friction but at the same time friction is the reason why much of our energy is wasted. Friction: A Necessary Evil | Advantages and Disadvantages of Friction | Class 8th Physics | 7. Teflon Why doesn’t anything stick to Teflon? - Ashwini Bharathula 8. Manipulating friction Rolling friction is much less than sliding friction. If you want to move a heavy object it is better to put some wheels or even logs under the object. This will reduce friction and make your work easier. (That is why invention of wheels changed our lives) Running on a football field is difficult with normal shoes and hence we use shoes with spikes that increase friction with the surface. In order to reduce friction cars are designed aerodynamically. In order to increase road grip for cars we need more friction. This can be done by using large tyres. Think of other ways in which you can manipulate friction. . Mass, Weight and Gravity 21 November 2021 18:36 Are Mass and Weight the same thing? | Physics | Don't Memorise The Difference Between Mass and Weight Less Than Five - What’s the Difference Between Mass and Weight? PowerPoints and Worksheets: <<Forces L3 Gravity Mass and Weight PowerPoint.pptx>> <<Gravity Calculations Worksheet.pdf>> <<Gravity Mass and Weight Worksheet LA.pdf>> <<Mass vs Weight Card Sort.pdf>> Check your weight on different plan https://theplanets.org/weight-on-planets/ Driving on other planets: What It's Like to Drive on Other Planets Newton's Laws 21 November 2021 18:03 <<1.Laws of Motion - First Law.PPTX>> Newton's First Law of Motion Newton's First Law of Motion | Forces and Motion | Physics | Don't Memorise What Is Newton's First Law Of Motion? The Dr.Binocs Show|Best Learning Videos For Kids|Peekaboo Kidz Inertia and Mass | Physics | Don't Memorise Newton's 1st Law - Inertia Newton's First Law of Motion - Science of NFL Football Simple Examples of Inertia Newton's First Law of Motion | Law of Inertia | Real Life Applications | Physics Newton's First Law of Motion | Forces and Motion | Physics | Don't Memorise Second Law of Motion <<2.Laws of Motion - Second Law.PPTX>> What Is Momentum? "A Tale Of Momentum & Inertia" - Short Film Newton's Second Law of Motion | Physics | Don't Memorise Newton's Second Law of Motion - Science of NFL Football Formula for Newton's Second Law Force = Mass x acceleration Force is directly proportional to mass. (More the mass more the force needed to move or stop the object) Acceleration is directly proportional to force. (More the force more would be the acceleration of an object) Acceleration is inversely proportional to mass (more the mass less would be the acceleration of an object pushed with the same force) Newton's Second Law of Motion (F=ma) | GCSE Physics | Doodle Science Accelerating Mass: F=ma Investigation of Second Law Investigating Newton’s 2nd Law Experimental Verification Of Newton's Second Law Of Motion Do this investigation yourself: <<Second Law Investigation.docx>> Worksheet on Second Law: <<Second Law_Worksheet.pdf>> Third Law <<3.Laws of Motion - Third Law.PPTX>> Newton's Third Law of Motion | Forces and Motion | Physics | Don't Memorise Newton's Third Law of Motion - Science of NFL Football Newton's Third Law of Motion | Real Life Examples | Physics Newton's third law - Best Demonstration EVER !! - by Prof. Walter Lewin Third Law – funny # Newtons 3rd law of motion- funny Another one � � � MAN KICK COW AND KARMA KICK HIM BACK� � � Worksheet: <<Worksheet 1_Newton's 3rd Law.pdf>> Revision: Newton's 3 Laws, with a bicycle - Joshua Manley Article on Newton's first law examples: https://blog.praxilabs.com/2021/06/07/newtons-first-law-of-motion-examples-in-everyday-life/ Article on applications of Newton's laws in daily life: https://blog.praxilabs.com/2021/02/24/applications-of-newtons-laws-of-motion-in-daily-life/ Link for self study: https://www.physicsclassroom.com/Physics-Interactives/Newtons-Laws Try this simulation: Forces and Motion: Basics
