VCE Physics Forces (Part 1) PDF

VCE PHYSICS CLICK TO EDIT [HSC/QCE/VCE] [SUBJECT NAME] CLICK UNIT 2 TO AOSEDIT 1: HOW [UNIT IS MOTION #] [AOSUNDERSTOOD? #]: [UNIT NAME] CHAPTER CLICK TO9:EDIT FORCES AND...

VCE PHYSICS CLICK TO EDIT [HSC/QCE/VCE] [SUBJECT NAME] CLICK UNIT 2 TO AOSEDIT 1: HOW [UNIT IS MOTION #] [AOSUNDERSTOOD? #]: [UNIT NAME] CHAPTER CLICK TO9:EDIT FORCES AND MOTION [LESSON GROUPING] NEW! Forces Click to(Part edit 1) lesson Presented by Patrick Robertson 1 © Patrick Roberston & Edrolo 2022 What's in this lesson? Study design dot points [model forces as vectors acting at the Click to edit KU headings + Representing forces1 superscript 1 point of application (with magnitude and direction)]1, labelling these forces using Newton’s first law Click to edit KU 2headings + the convention ‘force on A by B’ superscript 2 Newton’s second Click to edit KUlaw headings 3 + or on A by B superscript 3 [apply Newton’s three laws of motion]2 Click to edit KU headings + superscript 4 to a body on which forces act:[]3 Click to edit KU headings + and on A by B superscript 5 Click to edit KU headings + superscript 6 2 © Patrick Roberston & Edrolo 2022 Representing forces Key takeaway What are forces? Recap: From describing Forces are push or pull actions that have Forces act on objects by other objects. motion, we learnt a magnitude (in Newtons, N) and a There are contact and non-contact vectors have direction. forces. a magnitude and a direction. Remember Forces are vectors represented by arrows. to define one direction as being positive. Free body diagrams visualize all forces Friction (n.) acting on an object: A force that resists motion when two – The contact force is drawn objects are in contact. at the point of contact. – The non-contact force is drawn from the centre of the object. 3 © Patrick Roberston & Edrolo 2022 Multiple choice activity Which of the following statements about A. A force can only be exerted on contact with an forces is true? object. B. Forces are scalars with a magnitude. C. Forces are always caused by other objects. D. Friction forces can act at a distance. E. I don’t know. 4 © Patrick Roberston & Edrolo 2022 Multiple choice – response Which of the following statements about A. A force can only be exerted on contact with an object. forces is true? B. Forces are scalars with a magnitude. C. Forces are always caused by other objects. D. Friction forces can act at a distance. E. I don’t know. 5 © Patrick Roberston & Edrolo 2022 Newton’s first law A simulation 6 © Patrick Roberston & Edrolo 2022 Newton’s first law Key takeaway Deep dive Did you know? An object will accelerate only when An object remains at rest (stationary or at Newton’s first law it experiences a non-zero net force. a constant velocity) until an unbalanced is also called the force acts on it. Law of Inertia. The net force is the sum of all forces acting on an object. What this means: Spacecrafts don’t carry much fuel. Seat belts are life savers! The net force is found by adding up all the forces acting on an object (using vector addition) in each dimension Teacher’s tip! The net force is sometimes represented as 7 © Patrick Roberston & Edrolo 2022 which means the “sum of the forces”. Multiple choice activity Which of the following situations involves A. An ice skater moving across frictionless a non-zero net force? ice. B. A parachuter falling through the air at terminal velocity (constant velocity). C. A car coming to a stop at a red light without brakes. D. A stationary box on an inclined ramp. E. I don’t know. 8 © Patrick Roberston & Edrolo 2022 Multiple choice – response Which of the following situations involves A. An ice skater moving across frictionless a non-zero net force? ice. B. A parachuter falling through the air at terminal velocity (constant velocity). C. A car coming to a stop at a red light without brakes. D. A stationary box on an inclined ramp. E. I don’t know. 9 © Patrick Roberston & Edrolo 2022 Newton’s second law Newton’s second law (formula) or Key takeaway : acceleration (m s-2) The acceleration of an object is equal to the : net force (N) net force applied to an object divided by its mass. : mass (kg) Deep dive From Newton’s first law: an object needs a non-zero net force to accelerate. The magnitude of acceleration depends on the magnitude of force and the mass of an object. The direction of acceleration is equal to the direction of the net force. 10 © Patrick Roberston & Edrolo 2022 Worked example Whilst moving an 80 kg fridge, Freya and Georgia apply forces of 20 N and 30 N Newton’s second law respectively. There is an average frictional force of 5 N. (formula) or What is the acceleration of the fridge? : acceleration (m s-2) (2 marks) : net force (N) : mass (kg) Marking guide Key criteria Mark allocation Calculates the net force 1 mark States the acceleration with correct units 1 mark 11 © Patrick Roberston & Edrolo 2022 Multiple choice activity A 2000 kg car is accelerating up a highway. A. 1000 N Newton’s second law The driving force from the engine is 3000 N, (formula) and there are resistive forces (forces due to B. 2000 N or air resistance and friction) acting on it. C. 3000 N : acceleration (m s-2) : net force (N) If the car is accelerating at 2 m s-2, what is the D. 4000 N magnitude of the resistive forces? : mass (kg) E. I don’t know. 12 © Patrick Roberston & Edrolo 2022 Multiple choice – response A 2000 kg car is accelerating up a highway. A. 1000 N Newton’s second law The driving force from the engine is 3000 N, (formula) and there are resistive forces (forces due to B. 2000 N or air resistance and friction) acting on it. C. 3000 N : acceleration (m s-2) : net force (N) If the car is accelerating at 2 m s-2, what is the D. 4000 N magnitude of the resistive forces? : mass (kg) E. I don’t know. 13 © Patrick Roberston & Edrolo 2022 Summary Newton’s laws Net force What’s coming next Newton’s third law and First law: An object will accelerate only The sum of all forces acting on an types of forces when object in each dimension. it experiences a non-zero net force. Key term Friction Second law: The acceleration of an object is equal to the net force applied to an object divided by its mass: Newton’s second law (formula) or : acceleration (m s-2) : net force (N) : mass (kg) 14 © Patrick Roberston & Edrolo 2022 Image credits and further material links Further material links: Page 1: Janitor Turns Heads in Florida With 'Leaf Blower-Powered' Vehicle – YouTube video Page 6: PhET | Forces and Motion: Basics – Interactive media Image attribution: Pages 3, 7: Image by lobpreis / Pixabay.com license Page 10: Images © PhET Regular HTML Simulation Files / CC BY 4.0 Interactive media attribution: Page 6: PhET Interactive Simulations | University of Colorado Boulder – https://phet.colorado.edu Question sources: All questions are written by Patrick Robertson. 15 © Patrick Roberston & Edrolo 2022  The copyright in substantial portions of this material is owned by the Victorian Curriculum and Assessment Authority. Used with permission. The VCAA does not endorse this product and makes no warranties regarding the correctness or accuracy of its content. To the extent permitted by law, the VCAA excludes all liability for any loss or damage suffered or incurred as a result of accessing, using or relying on the content. Current and past VCAA exams and related content can be accessed directly at https://www.vcaa.vic.edu.au/. We do our best to make these slides comprehensive and up-to-date, however there may be errors. We'd appreciate it if you pointed these out to us! 16 © Patrick Roberston & Edrolo 2022