Transcript Forces and Motion

Forces and Motion
Motion
 What
do you think it means to be in
motion? How can we tell if something
is in motion?
Motion
 Motion:
a change in position, measured
by distance and time.
Frame of Reference
•
•
Determining if an object changes
position requires a frame of reference.
The object or point from which
movement is determined
 http://www.classzone.com/books/ml_scien
ce_share/vis_sim/mfm05_pg7_relmotion/
mfm05_pg7_relmotion.html
Frame of Reference
 Movement
is relative to an
object that appears stationary
 Earth is the most common
frame of reference
Speed
 Speed:
the distance traveled by a moving
object per unit of time
To calculate speed, use the equation
Speed = distance / time
 Speed
only gives distance and time!
Average Speed
 Average
speed: the speed of moving
objects is not always constant
 To
calculate average speed you look at
total time and distance
Average speed =
total distance / total time
Velocity
 Velocity
is speed in a given direction.
 Velocity gives distance, time, and the
direction of travel.
 Velocity changes by changing direction
or changing speed!
Calvin and Hobbes
Calculate Calvin and Hobbes Speed.
S=
D/T
50 yd/ 10 min
5 yd/min
Average Speed
 1.
What is your average speed if you take
2h to jog 8 miles ?
 Speed= distance/ time
 8m/2h= 4 mph
 2. What is the average speed of a car if it
travels 500 miles in 20 hours?
 Speed= distance/ time
500m/20h = 25 mph
Force
Force: any push or pull
Forces are measured in _____
A _____ is the combination of
all of the forces acting on an
object.
Forces
Force

Balanced Forces


forces acting on
an object that are
opposite in
direction and
equal in size
no change in
velocity
Balanced vs. Unbalanced
Forces
Balanced forces will not cause a
change in the motion of an object; they
have a net force of zero N.
 Examples
of balanced forces are:
 1. ______, 2. _____, 3. _____ .
Balanced vs. Unbalanced forces
 Unbalanced
forces could be best
described as
__________________________ .
 Examples
of unbalanced forces are
___________________________ .
Force Drawing
 Create
a drawing that shows an
example of balanced forces. The
drawing should show the forces
acting on the object and what
happens to the object if the forces
become unbalanced.
Forces
Forces
 You
and a younger brother or
sister are at a neighborhood pool.
Your brother or sister asks why
there are signs that say “NO
RUNNING!” What would be your
answer?
Forces
 _____
, ______ , and ______ are
examples of common lubricants.
 Therefore,
it is easier to slip when there is
water on the floor because the water acts
as a ______ that lessens the friction
between the bottom of your shoe and the
floor.
Pushing pedals, pressing
brakes, and kicking soccer balls
are all examples of forces.
A force is anything that changes the velocity of
an object.
But what’s a change in velocity?
A change in velocity is acceleration, so . . .
A force is anything that gives an object
acceleration.
NSF North Mississippi GK-8
Friction
 _____
is a force that opposes motion
between two surfaces that are in contact.
 A _____
is a substance that lessens
friction.
Friction

Friction
 force that opposes motion between 2 surfaces
 depends on the:
• types of surfaces
• force between the surfaces
 A _____ is a substance
that lessens friction.
Friction
 There
are four types of friction.
Friction

Four Types of Friction




Static Friction – force that acts on objects that
are not moving. (Couch Potato)
Sliding Friction - force that opposes the
direction of motion of an object as it slides over
a surface. (Ice skating or bobsledding)
Rolling Friction – friction force that acts on
rolling objects. (Rollerblading)
Fluid Friction – force that opposes the motion of
an object through a fluid. (Planes flying or
submarines traveling)
Friction
 Write
a story
that describes
what a day in
your life would
be like if there
was no
friction.
Gravity
Gravity
 Isaac
Newton discovered the ______
______ of Gravitation.
 Gravity
acts on any objects with mass.
Example: You and your books, pencils,
paper, etc.
Universal Law of Gravitation
 Mass
and gravity have a directly
proportional relationship.
 The
distance between the centers of
masses of the two objects and gravity
have an inversely proportional
relationship.
Differentiate between Mass and
Weight.
 Weight
is dependent upon the
acceleration due to gravity on a
particular planet.
 For
 The
instance: g on earth is 9.8 m/s²
larger the planet, the _____ the
gravitational force.