Matter in Motion

A Reference Point is: an object that appears to
stay in place

Motion: an object’s change in position
overtime relative to a reference point

Motion can be north, south, east, west, up and
down.

Common reference points are: the Earth’s
surface, trees, buildings, and sometimes other
moving objects
During the interval between the times
that these pictures were taken, the hotair balloon changed position relative to a
reference point—the mountain.
 Speed:
the distance traveled divided by the
time interval during which the motion
occurred
 Example:
Time = 10s and Distance=50m
Speed = distance ÷ time
= 50m ÷ 10s
= 5 m/s
 Standard
units (SI) for speed is meters per
second (m/s).
 Other



commonly used units are:
Kilometers per hour (km/hr)
Feet per second (ft/s)
Miles per hour (mi/h)
 Not
everything moves at a constant rate
though so you need to be able to calculate
average speed.
Average Speed =total distance
total time
 An
athlete swims a distance from one end of
a 50 m pool to the other end in a time of 25 s
 What
is the athlete’s average speed?
Step 1: Write the equation for average speed:
Average Speed =total distance
total time
Step 2: Replace the total distance and total
time with the values given, and solve
1.
Kira jogs to a store 72 m away in a time of
36 s. What is Kira’s average speed?
2.
If you travel 7.5 km and walk for 1.5 hr,
what is your average speed?
3.
An airplane traveling from San Francisco to
Chicago travels 1,260 km in 3.5 hr. What is
the airplane’s average speed?
 Velocity:
the speed of an
object in a particular
direction

Is like an object’s rate of
change of that objects
position

If speed and direction don’t
change then velocity is
constant, so constant
velocity is motion along a
straight line
The speeds of these cars may
be similar, but the velocities
of the cars differ because the
cars are going in different
directions.
 Resultant
Velocity: is a combination of 2 or
more velocities
 Acceleration:
the rate at which velocity
changes over time

An object accelerates if its speed, direction or
both change

Positive acceleration means an increase in
velocity

Negative Acceleration means a decrease in
velocity or what is called deceleration

faster the velocity changes, the greater the
acceleration is
Acceleration is measured in meters per second per second, or m/s2
A plane passes over point A a velocity of 240 m/s north.
Forty seconds later, it passes over point B at a velocity of
260 m/s north. What is the plane’s average acceleration?
Starting velocity = 240 m/s
Final velocity = 260 m/s
Time = 40 s
Plug in your numbers:
260-240 =
40 s
20m/s = 0.5m/s2 north
40s
What is the average acceleration of a subway
train that speeds up from 9.6 m/s to 12 m/s
in 0.8 s on a straight section of track?
 An
object traveling in a circular motion is
always changing its direction so its velocity is
always changing, so it’s accelerating.
 This
is called centripetal acceleration
The blades of these windmills
are constantly changing
direction. Thus, centripetal
acceleration is occurring
 Force:
a push or pull exerted on an object
in order to change the motion of the object

Force has size and direction
 Newton:
the SI unit for force,
symbol is N

All forces act on objects

Forces do not always cause motion


Example: you are exerting a force on
your chair, however the chair doesn’t
move. That is because the floor is
exerting a force on the chair 
You cannot see all forces! For
example the air around you is held
near Earth’s surface by the force of
gravity.
Something that you cannot
see exerts a force that
makes this cat’s fur stand
up.
The bulldozer is exerting a force on the pile of soil. But the
pile of soil also exerts a force by just sitting on the ground!

Net Force: the combination of all of the forces
acting on an object

When forces are moving in the same direction, you
add them together

When forces are moving in opposite direction you
subtract the smaller force from the larger one.

When the forces on an object produce a net force of
0N, then those forces are balanced

Balanced forces do not cause a change in motion of
an object

When the Forces of an object are not 0N, the forces
are unbalanced and a change in motion occurs.
When forces act in the same direction, you add the forces to
determine the net force. The net force will be in the same direction
as the individual forces.
When two forces act in opposite directions, you subtract the
smaller force from the larger force to determine the net force.
The net force will be in the same direction as the larger force.
Because all the forces on this house of cards are
balanced, none of the cards move.
The soccer ball moves because the players
exert an unbalanced force on the ball
each time they kick it
A boy pulls a wagon with a force of 6 N east
as another boy pushes it with a force of 4 N
east. What is the net force?
A dog pulls on his chew toy with a force of 10
N towards the east. His owner pulls on the
other end f the toy with a force of 15 N to
the west. What is the net force?
 Friction:
a force that opposes motion
between two surfaces that are in contact.

Can cause a moving object to slow down or
eventually stop

Occurs because the surface of any object is
rough
When the hills and valleys
of one surface stick to the
hills and valleys of
another surface, friction is
created
 Two
factors that affect the amount of
friction are:
1) the force pushing the surfaces together
and
2) the roughness of the surfaces.

If the force pushing objects together increases
then the hills and valleys come in closer
contact and the friction increases

The rougher the surface, the greater the
friction is
1.
Kinetic Friction: friction between moving
surfaces


2.
Mount depends on how the surfaces move
Sliding objects experience more friction than rolling
objects
Static Friction: when a force is applies to
an object but does not cause the object
to move


The force of the friction is balanced with the force
applied
Can be overcome with a large enough force

Lubricants: substances
applied to reduce friction
between objects (motor oil,
wax, grease, air on a hockey
table, etc)

Switching from sliding to
rolling friction (using ball
bearings in wheels)

Make surfaces that rub
together smoother (sanding
wood surfaces)
When you work on a bicycle, watch
out for the chain! You might get
dirty from the grease or oil that
keeps the chain moving freely.
Without this lubricant, friction
between the sections of the chain
would quickly wear the chain out.
 Make
surfaces rougher (sand on ice, textured
batting gloves, etc)
 Increase
the force pushing the surfaces
together (pressing harder on sandpaper)
No one likes cleaning dirty pans. To get
this chore done quickly, press down with
the scrubber to increase friction.
http://www.youtube.com/watch?v=efzYblYVUFk&feature=fvwrel
 Gravity:
a force of attraction between two
objects that is due to their masses

Gravity is a result of mass, so matter is affected
by gravity

Objects experience a pull toward all other
objects, called gravitational force

Because Earth has such a large mass, it also has
a very large gravitational force, pulling
everything toward its center
http://www.youtube.com/watch?NR=1&v=jwPc0kK9VHU&feature=fvwp

Proposed the idea of gravity

He said that an unbalanced force
on apples caused them to fall
from trees, and that an
unbalanced force on the moon
kept it circling the Earth; and
that both of these forces were
really the same, a force of
attraction called gravity

Wrote the Law of Universal
Gravitation, which describes the
relationships between
gravitational force, mass, and
distance
Sir Isaac Newton
realized that the
same unbalanced
force affected the
motions of the apple
and the moon
 Law
of Universal Gravitation: All objects in
the universe attract each other through
gravitational force; the size of the force
depends on the masses of the objects and
the distance between the objects.
http://www.youtube.com/watch?v=Jk5E-CrE1zg
1.
Gravitational Force Increases as
Mass Increases
2.
Gravitational Force Decreases as
Distance Increases
Venus and Earth have
approximately the same mass.
But because Venus is closer to
the sun, the gravitational
force between Venus and the
sun is greater than the
gravitational force between
Earth and the sun
The gravitational force between
objects decreases as the distance
between the objects increases. The
length of the arrows indicates the
strength of the gravitational force
between two objects
 Weight:
is a measure of the gravitational
force on an object; SI unit is Newtons (N)
 Mass:
is the amount of matter in an object;
SI unit is a kilogram (kg) but is also measured
in grams (g) or milligrams (mg)
http://www.youtube.com/watch?v=SegMt7sa42E
The Vomit Comet: http://www.youtube.com/watch?v=BTkFIE_-kL8