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

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 • 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»

Let’s watch this video

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?

Practice

To sum up

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

And now… it's up to you!

I’d like you to do something like this:

Good work!

Conclusions

To explore the topic…

… you can watch these two videos, too:

Video 1: http://study.com/academy/lesson/newtons-second-law-of-motion-the-relationship-between-force-and-acceleration.html

Video 2: http://study.com/academy/lesson/newtons-laws-and-weight-mass-gravity.html