Newton’s First Law. To know and apply Newton’s First Law. Identify the forces acting on the objects below: A + S C B N iron D F H J G I K E Newton’s First Law. To know and apply Newton’s First Law. Success criteriaIdentify the forces on a moving object Describe how an object is moving if the resultant force on it is 0 Apply Newton’s First Law to explain the motion of objects Describe inertia Newton’s First Law. To know and apply Newton’s First Law. Newton’s First Law“An object at rest stays at rest, or an object in motion stays in motion with the same speed and in the same direction, unless acted upon by an unbalanced force.” 1. What does this mean? 2. Re-write in in language that makes more sense. Newton’s First Law. To know and apply Newton’s First Law. Implications of Newton’s 1st Law • If there is zero net force on a body, it cannot accelerate, and therefore must move at constant velocity, which means • it cannot turn, • it cannot speed up, • What is Zero Net Force? The table pushes up on the book. FT A book rests on a table. Physics Gravity pulls down on the book. FG Even though there are forces on the book, they are balanced. Therefore, there is no net force on the book. SF = 0 Example An object will remain at rest or will continue to move with constant velocity in a straight line unless acted on by a resultant force. For a car parked on a hill at rest, the three forces (friction, weight and normal reaction force) sum to zero. Example An object will remain at rest or will continue to move with constant velocity in a straight line unless acted on by a resultant force. A vehicle moving at a constant velocity; resistive force are equal in size and act in opposite directions. the driving force and A short history lesson... Newton’s first law was actually discovered by Galileo NEWTON NICKED IT! A short history lesson... Galileo imagined a marble rolling in a very smooth (i.e. no friction) bowl. A short history lesson... If you let go of the ball, it always rolls up the opposite side until it reaches its original height (this actually comes from the conservation of energy) A short history lesson... No matter how long the bowl, this always happens... A short history lesson... No matter how long the bowl, this always happens... A short history lesson... No matter how long the bowl, this always happens... A short history lesson... Galileo imagined an infinitely long bowl where the ball never reaches the other side Resultant force: The resultant force is the single force that can replace a number of forces acting on an object. Example 1: The resultant force here is 2 N to the left. The forces are unbalanced, they will cause the object to move to the left. 7N 5N Example 2: The resultant force here is 0 N. The forces are balanced, they will have no influence on the motion of the object. 3N 3N Newton’s First Law. To know and apply Newton’s First Law. What is happening when … • A person is standing still • A stationary boat is on still water • A skier is travelling at a constant speed • A parachutist is falling at terminal velocity • A stationary block is on a tilted ramp In each case, we have no resultant force Mini Wboards 2000 N 6000 N 300 N 3000 N 2000 N 6000 N 4000 N 3000 N 1500 N 4000 N 1000 N 2000 N 7N What is the resultant force on the block? 3N 10N 20N 13N Show your working. 10N Mini Wboards state whether the objects are under balanced or unbalanced forces: 4N 3N A D 4N 5N 3N B 2N 3N C 2N E 2N 2N 2N F 4N G 4N 2N Laws Of Motion Inertia- the tendency for an object to resist changes in motion - a moving object keeps moving - an object at rest stays at rest Both the car and the driver are moving at 60 mph. The car hits a cement road divider and is stopped. The driver, who is not wearing his seat belt, will continue to move at 60 mph. http://www.physicsclassroom.com/mmedia/newtlaws/cci.cfm Newton’s First Law – Law of Inertia An object that is moving at a constant velocity, (or is at rest), does not change its state of motion, unless a net force acts on it. Inertia – (1st Law) A moving object keeps moving http://www.physicsclassroom.com/mmedia/newtlaws/il.cfm http://teachertech.rice.edu/Participants/louviere/Newton/law1.html Likewise, an object at rest wants to remain at rest. An object at rest remains at rest. https://www.youtube.com/watch?v=ZJxIS53Yt8s Newton’s First Law. To know and apply Newton’s First Law. What affects inertia? • Massive objects like space shuttles have a large amount of inertia. • The ISS has a mass of 400,000kg and is in low Earth orbit on average about 350km above the surface of the Earth, travelling at 7700m/s (about 17,0000mph). Bigger mass means… Newton’s First Law. To know and apply Newton’s First Law. • http://www.youtube.com/watch?v=8qB-tvEnVrU The tool bag became unattached and due to inertia started to move away from the astronaut. Until it burnt up on re-entering the Earth’s atmosphere, it was a small piece of space junk in orbit around Earth moving in a circular orbit. This is due to the attraction of the force of gravity and moving at the same speed forever. Friction Friction is a common force. It is experienced whenever 2 things try to slide over each other. In each of the following pictures decide where the friction is and if it is useful or a nuisance or both! 1. 2. 30 Summary: Resultant force: The resultant force is the single force that can replace a number of forces acting on an object. Any object can be: stationary moving constant velocity Balanced forces Balanced forces Changing velocity (accelerating/decelerating) Unbalanced forces Quiz- The van here is moving at constant velocity, What is a possible value of the force A ?N a. 0 N b. 50 N c. 100 N d. 150 N 100N The hot air balloon here is accelerating upwards, what is a possible value of its uplift force? ? N a. 0 N b. 500 N c. 1000 N d. 2000 N 1000 N The hot air balloon here is accelerating upwards, what is a possible value of its uplift force? ? N a. 0 N b. 500 N c. 1000 N d. 2000 N 1000 N The helicopter here is stationary, What is a possible value of its weight? 2000 N a. 0 N b. 1000 N c. 2000 N d. 4000 N ? N The helicopter here is stationary, What is a possible value of its weight? 2000 N a. 0 N b. 1000 N c. 2000 N d. 4000 N ? N The plane here is decelerating, what is a possible value of the engine force? 700 N a. 0 N b. 700 N c. 1000 N d. 1400 N ?N The plane here is decelerating, what is a possible value of the engine force? 700 N a. 0 N b. 700 N c. 1000 N d. 1400 N ?N The car here and is decelerating, what is a possible value of the braking force? ?N a. 0 N b. 500 N c. 1000 N d. 1500 N 1000 N The car here and is decelerating, what is a possible value of the braking force? ?N a. 0 N b. 500 N c. 1000 N d. 1500 N 1000 N The car here has a mass of 1000 kg, calculate the deceleration? 1000 N 1500 N a. 0 m/s2 b. 0.5 m/s2 c. 2.0 m/s2 d. 5.0 m/s2 The car here has a mass of 1000 kg, calculate the deceleration? 1000 N 1500 N a. 0 m/s2 b. 0.5 m/s2 c. 2.0 m/s2 d. 5.0 m/s2 Find someone who… 1. How do we represent forces? 2. What do we measure forces in? 3. What is meant by balances forces? 4. What is meant by unbalanced forces? 5. When would an object move left? 6. What is friction? 7. What is a resultant force? 8. When will a car accelerate? 9. How does a ball thrown in space move? 10. Why does the ball move like this? 11. When does a car move at a constant speed? 12. If the resultant force is zero... Find someone who… 1. How do we represent forces? 2. What do we measure forces in? 3. What is meant by balances forces? 4. What is meant by unbalanced forces? Newtons Forces in opposite directions that are the same size Forces in opposite directions that are different sizes 5. When would an object move left? 6. What is friction? 7. What is a resultant force? 8. When will a car accelerate? If left force is larger Force that slows down movement when 2 surfaces touch Overall force acting on an object, size and direction When force on it to accelerate is larger 9. How does a ball thrown in space move? 10. Why does the ball move like this? 11. When does a car move at a constant speed? 12. If the resultant force is zero... Will continue to move in the same direction at the same speed No opposing force, no friction Push, pull, spin, move Arrows, directions, sizes, N Either not moving or constant speed When both forces in opposite directions are balanced, no resultant force 4 Marks Grade 4 You have 4 minutes. 1 minute per mark. 4 Marks Swap your paper with the person next to you and use the mark scheme to mark your paper. Don’t forget to mark your questions using a green pen. How did you do? 2 Marks Grade 5 You have 2 minutes. 1 minute per mark. 2 Marks Swap your paper with the person next to you and use the mark scheme to mark your paper. Don’t forget to mark your questions using a green pen. How did you do?
