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Chapter 5
Matter in Motion
Motion is a change in position.
A reference point is a place or
object used for comparison to
determine if something is in
motion.
(see pg 118)
Speed is the change in position
of an object per unit of time (the
“rate of change” in position).
-is always positive
-is nondirectional
speed = distance
time
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v=d/t
Velocity is the speed of an
object and its direction.
-may be a negative depending
on direction.
Instantaneous speed is the
speed of an object at any given
instant.
Average speed is the total
distance traveled divided by the
total time of travel.
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total
distance
avg speed =
total time
Acceleration is the rate at which
velocity changes.
Acceleration refers to:
 Increasing speed
 Deceleration (decreasing speed)
A negative acceleration!
 Changing direction
Acceleration formula:
acceleration =
final velocity - initial velocity
time of change
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Vf - Vi
a=
t
(practice problems)
Centripetal acceleration occurs
to objects traveling in circular
motion (even if it is at constant speed).
 The direction of the object (and
therefore its velocity) is constantly
changing, so the object is constantly
accelerating!
A force is a push or a pull.
 forces have size & direction
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Forces are measured in units
called newtons (N).
Two forces can combine so that
they add together, or subtract
from each other. They may also
cancel each other out.
The overall force on an object
after all forces are added
together is called the net force.
Unbalanced forces acting on an
object will change the object’s
motion.
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Equal forces acting in opposite
directions are called balanced
forces.
(balanced forces will NOT change the
motion of an object!)
Friction is a force that opposes
motion between two surfaces
that are in contact.
Types of friction:
 static friction is friction when
an object is not moving.
(static friction disappears as soon
as an object starts moving)
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 kinetic friction is friction
between moving surfaces.
-sliding friction
-rolling friction
-fluid friction
Gravity is a force of attraction
between objects due to their
masses.
All objects have mass. Gravity is a
result of mass. Therefore, all
objects have and are affected by
gravity.
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The Law of Universal
Gravitation:
The force of gravity acts
between all objects in the
universe.
 The force of gravity varies
with mass and distance.
Differences in mass
small
mass
large
mass
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Differences in distance
Weight is a measure of the
force of gravity on an object
(use newtons).
-may change depending on location.
Mass is the amount of matter in
an object (use grams).
-does not change.
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measures
unit
what affects it?
mass
weight
amount of matter
force of gravity
kg
N
does not
change
may change
due to location
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