Transcript File force and motion notes 2010

DESCRIBING MOTION
Motion - an object’s change in
position relative to a reference point
over a period of time
Reference Point – an
appears to stay in
object
place
that
Motion is ____________
relative to a reference point
that is ______________
relevant for the situation
EXAMPLE 1:
Two horses are standing side by
side. One of them moves. How can
you tell which one has moved?
Click me to see the
two horses
standing side by
side.
Click me to see the
two horses after
one has moved.
EXAMPLE 2:
Two horses are standing side by
side. One of them moves. How can
you tell which one has moved?
Click me to see the
two horses
standing side by
side.
Click me to see the
two horses after
one has moved.
Buildings, trees, and mountains are all useful reference points.
DISTANCE
Distance – how
from starting
far
it is
point to
point in any
stopping
direction
; the total
length
of the path traveled
End
Follow all the loops
Start
DISPLACEMENT
Displacement - measures the
distance and direction
starting
between the
position and the ending position
Think: “As the bird flies” – straight line path in ONE direction.
Start
End
DISTANCE & DISPLACEMENT
DISTANCE
DISPLACEMENT
A
D
Displacement
Distance
C
B
SPEED
Speed – the distance traveled
divided by the amount of time
EXAMPLE: A dog ran 25 miles in 5 hours. His
speed is 5 miles per hour.
(25 miles ÷ 5 hours)
Average speed = total distance
total time
MOTION GRAPHS
graph
Motion can be plotted on a _________
with time on the horizontal axis and
distance on the vertical axis.
This distance-time
graph shows
how the distance
traveled by a
sprinter changed
during a 100-m
race.
In the graph below, what was the sprinter’s
average speed over the entire race?
Average speed = total distance
total time
Avg. Sp. =
100 m
12 seconds
Avg. Sp. = 8.33 m/s
Here’s a Riddle:
Two birds leave the same tree at the
same time. They both fly at 10 km/h for
1 hour, 15 km/h for 30 minutes, and 5
km/h for 1 hour. But they don’t end up
at the same place. Why not?
The birds were flying in different
directions! Their speed was the same,
but the direction they flew was
different. So, their VELOCITIES
differed.
VELOCITY
Velocity – the measure of
direction
particular
speed
EXAMPLE: 5 miles per hour west
in a
ACCELERATION
Acceleration – the change
divided by the amount of time
which the change occurs
in velocity
over
Acceleration can take place when an
object changes
direction ,
speed , or both.
FORCE
Force – a push or a
that has size and direction
The motion of an object
when a force acts on it.
pull
changes
Force makes objects speed up, slow
down, or change direction. Force causes
acceleration.
INERTIA
Inertia – measures an object’s tendency to
resist changing its motion
and depends on the amount of mass an
object has.
INERTIA EXAMPLE 1
The more mass an object has, the
greater
its inertia.
An elephant has more
inertia than a mouse
because the elephant has
more mass
INERTIA EXAMPLE 2
The more inertia an object has, the
less effect a force has on its motion.
If you kick an empty box and a full box with the same
amount of force, the full box will not move as far.
INERTIA EXAMPLE 3
The more inertia an object has, the harder it
is to start the object moving or slow it down.
Is it easier to push a Volkswagen Beetle or
an 18-Wheeler Truck?
BALANCED FORCES
Balanced Forces – forces that cancel
each other out because they are equal
and acting in opposite directions.
The object’s motion does not change.
Both forces pushing on the
box are opposite and equal.
5N
5N
The object won’t move.
UNBALANCED FORCES
Unbalanced Forces – do
each other out.
NOT
cancel
change
An object’s motion will
unbalanced forces act on it.
if
Net force is the difference between two
_______
forces.
Net Force Example
15N
15 Newtons of
force to the right
5N
5 Newtons of force
to the left
Net Force = 10 Newtons with motion to the right
UNBALANCED FORCES
1000 Newtons
500 Newtons
The forces shown above are PUSHING / PULLING forces .
UNBALANCED FORCES
1000 Newtons
500 Newtons
The forces shown above are WORKING TOGETHER /
OPPOSITE FORCES.
UNBALANCED FORCES
1000 Newtons
500 Newtons
The forces are EQUAL / NOT EQUAL.
UNBALANCED FORCES
1000 Newtons
500 Newtons
The forces DO / DO NOT balance each other.
UNBALANCED FORCES
1000 Newtons
500 Newtons
The net force is 500N TO THE RIGHT /
500N TO THE LEFT / ZERO.
UNBALANCED FORCES
1000 Newtons
500 Newtons
There IS / IS NO motion.
FRICTION
force that exists between
Friction – a
two touching surfaces
Friction is present in almost all motion.
Friction occurs between any two surfaces that
slide past each other.
FRICTION
Friction between the
tire and the ground
helps the wheels on
this car turn without
slipping.
FRICTION
Air Resistance is the pushing of
______________________
air against the surface of an object.
EXAMPLE:
You feel air resistance when you place your
hand in the air rushing past a moving car.
GRAVITY
force
Gravity – the
that all objects
with mass exert on other matter.
Gravity is affected by:
______________
- amount of matter in an
Mass
object
______________Distance how far away an object is
GRAVITY
Weight the measure of the
__________gravitational force between an object and
the planet or moon where the object is.
If you weigh 100
pounds here on
Earth…
…then your weight
on the Moon would
be 17 pounds!