Newton’s Second law of motion Chapter 1 CLIL LESSON of PHYSICS III A LICEO LINGUISTICO A. S. 2014/2015 Prof. ssa Anna Lucia Daniele Prof. ssa Anna Maria De Francisci Lead-in force “An impressed force is an action exerted upon a body, in order to change its state, either of rest, or of moving uniformly forward in a right line.” (Newton, Definition IV, The Mathematical Principles of Natural Philosophy) • Is a vector quantity; • its magnitude is measured in newtons (N) with a dynamometer. examples • hitting a ball with a bat • pulling with your hand on a fishing line • electric force • force of friction between your sneakers and the floor • gravitational force • magnetic force Introduction Question for you: What happens if a force acts upon a moving object? Try to answer 1) If the force acts in the direction of motion, the velocity of the object increases. 2) If the force acts contrary to the direction in which the object is moving, its velocity decreases. In both cases we have a variation of velocity, that is an… Expressing Newton’s Second Law Newton’s Second Law of motion: «The acceleration of an object moving in an inertial reference frame is proportional to the net force acting on it and inversely proportional to its mass» Question: What can you say about acceleration by looking at this formule? (Try to answer) Let’s watch this video Newton’s 2nd law of motion The net force on an object is equal to the product of its mass and acceleration or r r F ma Newton’s 2nd law enables us to compare the results of the same force exerted on objects of different mass. inertial mass & weight inertial mass symbol definition SI unit of measurement m • is a scalar quantity • is a measure of an object’s resistance to changing its state of motion or rest when a force is applied • is determined by applying a force to an object and measuring the acceleration that results from that force kg weight W • is a vector quantity • acts downwards, towards the centre of the Earth • is equal to the gravitational force that the Earth exerts on an object W = mg N learning the basics 1. 2. An object of 2 kg mass, acted upon by a net force of 20 N, will experience what acceleration? 5.00 m/s2 a b 10.0 m/s2 c 7.50 m/s2 d 12.4 m/s2 If a net force is acting on an object, then: a the object is at rest. b the object is moving with constant velocity. c the object is being accelerated. d the object is losing mass. 3. A 1,500 kg car is moving with an initial velocity of 20 m/s and comes to a stop in 5 seconds. What is the magnitude of the net force acting on the car? Practice To sum up Glossary English word Italian meaning Acceleration Act upon Apply Arrow Axis Dynamics Friction Hit Inertial Inertial reference frame Magnitude Net force Rest Resultant Scalar Undergo Vector Velocity accelerazione agire su applicare freccia asse (direzione) dinamica attrito colpire, urtare inerziale sistema di riferimento inerziale intensità (modulo) forza netta riposo, fermo risultante scalare subire vettore velocità Conclusions And now… it's up to you! I’d like you to do something like this: Good work! To explore the topic… … you can watch these two videos, too: Video 1: http://study.com/academy/lesson/newtons-second-law-of-motion-therelationship-between-force-and-acceleration.html Video 2: http://study.com/academy/lesson/newtons-laws-and-weight-massgravity.html