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# FORCES

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• pg 1
```									FORCES
What is a force?
• A force is a PUSH or a PULL.
• Forces do not have mass nor do they
occupy a space.
• Forces can
– tear, bend, twist, or stretch an object.
– Change the direction of the motion
• Measured in Newtons (N)
2 main types of forces
• Contact forces
– A force between two objects in direct contact
with one another.
Frictional
• Non-Contact forces
– Forces that can act on objects at a distance
and between two objects which are not in
direct contact with one another.
Magnetic
Gravitational
Gravitational Force
• Pulls objects towards the center of the earth
• Objects exert a force of attraction on all
objects around it.
– The force may be small that we can’t feel it.
• The larger the mass, the stronger the
gravitational force
– The sun’s gravitational force pulls smaller bodies
towards it
• The closer the two objects are, the stronger
the gravitational force
Gravitational force
• Objects fall to the ground at the same rate,
regardless of their mass in the absence of
air
• Overcoming gravity:
– Energy is needed to overcome gravity
– More energy if you’re going against it
– Less energy if you’re going towards it.
Gravitational energy in our daily
lives
Frictional Force
• A force that opposes motion.
• Produced when two surfaces are in contact
with each other
• Can cause an object to move slower
• More friction is exerted if the object’s mass is
great
• Surfaces play a role in the amount of friction
generated
Frictional Force
• Types of friction
– Sliding
• Two solid objects with one object sliding over the other
• snowboarding
– Rolling
• When a circular object rolls over a surface
• cycling
– Fluid
• Involves a solid object moving through a wet or fluid (liquid or
gas)surface
• Parachuting, wakeboarding
Infer the friction generated in the
given pictures
Frictional energy
• Energy is required to overcome friction.
• How much energy is needed to overcome
friction over smoother surfaces?
• How much energy is needed to overcome
friction over rougher surfaces?
• When is frictional energy beneficial? When
is frictional energy harmful?
Frictional energy in our lives
Magnetic Force
• A force of attraction that pulls unlike poles.
• A force of repulsion that pushes like poles.
• A MAGNET attracts magnetic materials,
which include those made up of Iron, steel,
cobalt and nickel
Magnetic force
• A stronger magnet exerts a stronger force
of attraction
– The material may move faster
– A stronger force is needed to overcome a
stronger magnet

N              S         N                    S
Magnetism in our daily lives
The PENDULUM
String

Metal ball

gravity
The PENDULUM
• Found in clocks; has a weight and a string
• Air resistance (frictional force) and gravity
affect the motion of the pendulum
• The length of the string also affects the
time for the pendulum to complete its
swings

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