Download Friction and Gravity

FORCES
Lesson 3
Friction and Gravity
What is a Force? (p.44)
A push or a pull on an object in a
particular direction.
CONTACT FORCES (P.44)
Force through CONTACT:
*Virtually all actions require a…
NON-CONTACT FORCES (P.46)
Does not require contact:
Magnetic:
Static:
Gravity:
Forces are measured in
NEWTONS
GRAVITY (P.47)
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 (P. 48)
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.
Gravity Tube Demonstration
TRY THIS
Take away ALL
air, so that only
the force of
Gravity is being
used.
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.
UNIVERSAL GRAVITATION
The law of universal gravitation states that the
force of gravity acts between all objects in the
universe.
(1:47 min)
WHAT IS FRICTION?
Friction is a force that resists the motion of
two surfaces that are touching.
(P.49)
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.
TRY THIS
When FRICTION just isn’t there
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
Friction
In
Daily
Life
(5:41 min)
A WORLD WITHOUT FRICTION (2:41 MIN)
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.