# What is the gravitational force of attraction?

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an invisible force that pulls objects toward each other. Earth's gravity is what keeps you on the ground and what makes things fall. Anything that has mass also has gravity. Objects with more mass have more gravity.
1. FORCES
Lesson 1
Friction and
Gravity
2. What is a Force? (p.44)
A push or a pull on an object in
a particular direction.
3. CONTACT FORCES (P.44)
Force through CONTACT:
*Virtually all actions require a…
NON-CONTACT FORCES (P.46)
Does not require contact:
Magnetic:
Gravity:
Forces are measured in
NEWTONS
4. 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.
5. WEIGHT VS MASS (P. 48)
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
6. 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.
7. GRAVITY AND FREE FALL
Take away ALL
An object is in free fall when the only air, so that only
force acting on the object is gravity. the force of
Gravity is being
Free-falling objects do not encounter used.
air resistance.
In free fall, the force of gravity is an
unbalanced force.
Gravity Tube Demonstration
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THIS
8. 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.
9. UNIVERSAL GRAVITATION
The law of universal gravitation states that the force of gravity
acts between all objects in the universe.
Gravity, Force and Work
(1:47 min)
10. WHAT IS FRICTION? (P.49)
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
11. 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.
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12. When FRICTION just isn’t there
Friction – Bill Nye
13. SLIDING FRICTION
•A resistance to movement that is created when
two things rub together.
14. WAYS TO REDUCE FRICTION
Smooth the surface / Put ball bearings in wheels
Replace rolling with sliding / Add oil or another type of lubricant
When friction in daily life