1. Physics & Chemistry Department
UNIT 5. FORCES
2nd ESO
5. SUMMARY
Most forces are either a push or a pull .
Forces can:
a) change the shape of an object
b) Change the lenght of an object.
c) Make something speed up or slow down .
d) Make something move or stop .
e) Change the direction of movement.
But they can never change the mass of an object.
Forces can be classified into:
Friction: it acts in the opposite direction of
movement.
Air resistance :force acting in the opposite
Contact forces direction of movement when an object moves
through the air.
Push
Pull
Upthrust : force that pushes an object up in a
liquid.
Magnetic forces: forces between magnets (N, S)
opposite poles attract
like poles repel
Non-contact Electric forces: forces between charges (+, -)
forces opposite charges attract
like charges repel
Gravitational forces: forces between masses
they are always forces of attraction
Unit 5. Forces 1

2. IES Llorenç Garcías i Font María Pérez Galván; Emma Sánchez Clark
Physics and Chemistry Department
Contact forces are not classified as forces of attraction or repulsion.
Mass is the amount of matter in a body. Its units are kilograms. It is measured
using a balance. It is always the same on any planet.
Weight is the force of attraction between an object and the planet .
Its units are newtons. It is measured using a force meter. It depends on the planet.
The weight of an object is calculated using this equation: W=m·g
In this formula mass is expressed in kilograms and the value of gravity
depends on the planet you are on (Earth’s gravity is 9.8 m/s2 and Moon’s
gravity is 1.6 m/s2).
When the resultant force acting on an object is zero, we say that the forces are
balanced. If the resultant force is not zero the forces are not balanced.
How does the state of motion of an object change when the forces acting on it
are balanced or not?
Balanced forces: the object will not move .
For a steady
Unbalanced forces: the object will start moving
object in the direction of the net force
Balanced forces: the object will move at a constant
speed
For a moving
Unbalanced forces:
object
The object will accelerate if the net
force acts in the direction of movement.
The object will slow down if the
net force acts in the opposite direction of
movement.
Unit 5. Forces 2

3. IES Llorenç Garcías i Font María Pérez Galván; Emma Sánchez Clark
Physics and Chemistry Department
6. GLOSSARY [30 WORDS]
air resistance resistència/resistència aerodinàmica
arrow fletxa
balanced forces forces en equilibri
constant speed velocitat constant
contact forces forces per contacte
direction direcció
drawer calaix
driving force força motora/força motriu
electric force força elèctrica
force força
force meter dinamòmetre
force of attraction força d’atracció
force of repulsion força de repulsió
friction força de fricció/força de fregament
gravitational force força gravitatòria
gravity gravetat
magnetic force força magnètica
mass massa
motion movement
non-contact forces forces a distància
shape forma
spring molla
still aturat
to pull estirar
to push empenyer
to slow down frenar
to speed up accelerar
unbalanced forces forces que no es troben en equilibri
upthrust força ascensional/empenyiment
weight pes
Unit 5. Forces 3