force - Liceo Megara

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