Post on 21-Jan-2021
UNIT 3.3 – FRICTION
AND GRAVITY
FRICTION
Friction - the force that two surfaces exert on
each other when they rub against each other.
The amount of friction is determined by two
factors:
1. How hard the surfaces push together
2. The type (roughness) of the two surfaces
4 Types of Friction
1. Static Friction- friction between 2 things not
moving past each other
2. Sliding Friction- friction between 2 things
that are moving
3. Rolling Friction- friction between a rolling
object and the object it rolls on
4. Fluid Friction – friction that occurs when a
solid object moves through a fluid (liquids and
gases are fluids)
Copyright 2009 Pearson-
Motion, Forces, and Energy
Gravity
Gravity – a force that pulls objects toward each other Anything that has mass can cause a
gravitational force
Law of Universal Gravitation – the force of gravity acts between all objects in the universe.
Factors Affecting Gravity
There are two factors that affect gravitational attraction between two objects:
1. Mass – amount of matter an object has
2. Distance – how far the two objects are from each other
Weight vs. Mass
Mass – how much matter an object has.
Weight – the force of gravity on a person
Weight = Mass x Gravity
Free Fall
Free Fall – when
the only force acting
on an object is
gravity
During free fall,
gravity is an
unbalanced force!
Free Fall
During free fall, objects
accelerate (or increase
velocity)
Acceleration due to gravity
is 9.8 m/s2
A ball starts at 0 m/s
After 1 second, its velocity is
9.8 m/s
After 2 seconds, its speed is
19.6 m/s (9.8 m/s + 9.8 m/s )
Air Resistance
Theoretically, all
objects are supposed
to fall at the same rate
(due to free fall).
Air Resistance – fluid
friction experienced by
objects falling
The leaf experiences
more air resistance
Projectile Motion
Projectile – an object that is thrown
Projectile Motion occurs when you throw a ball in any direction except vertically (up or down).
As a ball is dropped vertically, the ball in projectile motion is thrown at the same time. They will land on the ground at the same time as well.
This is because the force of gravity acts on both balls the same way, in a downward direction.
Friction Gravity
Effect on motion Opposes motion Pulls objects toward one
another
Depends on
Types of surfaces
involved, how hard the
surfaces push together
Mass and distance
Measured in Newtons Newtons
- Friction and Gravity
Comparison Chart