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FORCES
Lesson 1
Friction and Gravity
What is a Force?
A push or a pull on an object in
a particular direction.
CONTACT FORCES
Force through CONTACT:
*Virtually all actions require a…
NON-CONTACT FORCES
Does not require contact:
Static
:
Magnetic:
Gravity:
Forces are measured in
NEWTONS
GRAVITY
An attractive force that exists
between all objects that have
mass.
This force is dependent on mass
and distance from the object.
WEIGHT VS MASS
Mass:
Amount of matter in an object.
What is the difference?
Weight: Is the gravitational force
exerted on an object.
Your weight is actually a force measured in Newton’s.
Demonstration: Mass & Gravity
LINK
GRAVITY AND AIR RESISTANCE
Most objects falling through air
experience a type of fluid friction
called air resistance.
Air resistance is not the same for all
objects.
The greater the surface area of the
object the greater the air resistance.
(paper drop)
However, since the elephant has more
mass, it has more downward force of
gravity and falls faster.
GRAVITY AND FREE FALL
An object is in free fall when the only
force acting on the object is
gravity.
Free-falling objects do not encounter
air resistance.
In free fall, the force of gravity is an
unbalanced force.
Take away
ALL
air, so that
only
the force of
Gravity is
being
used.
GRAVITY AND FREE FALL
Gravity Tube Demonstration
Video link
https://www.youtube.com/watch?v=z_sJ15feNGw
CALCULATING FREE FALL
All objects in free fall accelerate at the same
rate – 9.8 m/s² - regardless of their mass.
in one second = 9.8 m/s²
in two seconds = 19.6 m/s²
in three seconds = 29.4 m/s²
in four seconds = ________
The velocity continues to increase as the object
falls.
LAW OF UNIVERSAL GRAVITATION
The law of universal gravitation states
that the force of gravity acts between
all objects in the universe.
https://www.youtube.com/watch?v=Jk5
E-CrE1zg
WHAT IS FRICTION?
Friction is a force that resists the motion of
two surfaces that are touching.
When a moving object comes in contact with another
object, friction is the opposing force that slows or
stops the moving object.
*Static…prevents objects sliding
*Sliding...resists objects while they are moving
*Fluid…air
or water
Without friction, an object would continue to
move at constant speed forever.
The strength of the force of friction depends on
the type of surfaces and how hard the
surfaces push together.
Rough surfaces produce greater friction than
smooth surfaces.
Types of friction
Video link
https://www.youtube.com/watch?v
=MAqrWvkBoHk&feature=youtu.be
SLIDING FRICTION
•A resistance to movement that is created
when two things rub together.
WAYS TO REDUCE FRICTION
Smooth the surface / Put ball bearings in wheels
Replace rolling with sliding / Add oil or another type of
lubricant
Video link
https://www.youtube.com/watch?v=mrnQGTG
o3ZU
A WORLD WITHOUT FRICTION
Video link
https://www.youtube
.com/watch?v=VUfqj
SeeZng&list=PLB6cN
Wa8De8scFYktaZ10avaNNQG
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FLUID FRICTION
The force that tries to slow objects down when
they move through a liquid or a gas. It's also
known as "drag", or "air resistance".
All gases and liquids are fluids.
An airplane and a swimmer both experience
fluid friction.