Chapter 1
Newton’s Second law of motion
CLIL LESSON of PHYSICS
III A LICEO LINGUISTICO
A. S. 2014/2015
Prof. ssa Anna Lucia DanieleProf. ssa Anna Maria De Francisci
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 • force of friction between• pulling with your hand your sneakers and the floor on a fishing line • gravitational force• electric 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
Question:What can you say about acceleration by looking at this formule?(Try to answer)
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»
Newton’s 2nd law of motion
The net force on an object is equal to the product of its massand acceleration or
Newton’s 2nd law enables us to compare the results of the same force exerted on objects of different mass.
r F m
r a
inertial mass & weight
inertial mass weight
symbol m
definition • 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 measuringthe acceleration that results from that force
• is a vector quantity• acts downwards, towards the centre ofthe Earth
• is equal to thegravitational force thatthe Earth exerts on an object
SI unit of measurement kg N
learning the basics
1. An object of 2 kg mass, acted upon by a net force of 20 N, will experience whatacceleration?
a 5.00 m/s2
b 10.0 m/s2
c 7.50 m/s2
d 12.4 m/s2
2. 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?
Glossary
English word Italian meaningAcceleration accelerazione
Act upon agire suApply applicareArrow frecciaAxis asse (direzione)
Dynamics dinamicaFriction attrito
Hit colpire, urtareInertial inerziale
Inertial reference frame sistema di riferimento inerzialeMagnitude intensità (modulo)Net force forza netta
Rest riposo, fermoResultant risultante
Scalar scalareUndergo subireVector vettore
Velocity velocità