Transcript What is the unit for force?

Catalyst
1.What is the unit for force? Newton (N)
2. What is the force weight of a 45 kg desk?
441 N
3. Give a scenario example for each of
Newton’s Laws.
HANDS UP!!
4. What is net force? Give an example.
Total of ALL forces acting on an object
Gravity
Gravity is a force of
attraction between
objects caused by their
masses
All matter has mass.
Gravity
Gravity is a result of mass.
So, all matter is affected by gravity.
ALL objects have a gravitational
attraction to each other – YES, ALL
OBJECTS! We don’t notice this
attraction because it is so small that it
appears insignificant.
WHY??
Why must you exert a force to
pick up an object? What must
you overcome?
You must overcome GRAVITY
to lift any object.
Fig, I mean Isaac Newton!
Isaac Newton…
The Falling Apple story…Newton
sat under a tree and saw an apple
fall and thought there had to be
forces at work – he called the force
gravity.
7 Steps that led Newton to being
considered the “MAN”
Step1—Understand Galileo’s concept of Inertia.
 Any change in speed or direction requires a force.
Step 2—Sit under apple tree.
Step 3—See apple falling on head; see moon through trees.
Step 4—Realize that the moon must be falling
towards the earth, just like the apple!
Step 5— Wonder why moon circles Earth.
Step 6— Conclude that a centripetal force must be pulling the
moon into circular motion.
Step 7—Figure out that the moon falls for the same reason
that the apple falls—both are pulled by EARTH’S
GRAVITY.
Universal Law of Gravitation
Part 1: Gravitational force Increases as
MASS Increases.
Part 2: Gravitational force Decreases
as DISTANCE Increases.
It is valid EVERYWHERE in the
UNIVERSE!
Larger mass = Larger Gravitational
force; Smaller mass = Smaller
Gravitational force
Diagram it!
How Universal Gravitation relates to
Newton’s First Law…
The moon will remain in motion in a
straight line if it were not acted upon by an
outside force (the Earth’s gravity pulling on
it).
Weight vs. Mass
Weight is a measurement of how hard gravity is
pulling on that object.
Your weight depends on how much gravity is
acting on you at the moment and varies by your
location
Mass: amount of matter in an object; does NOT
change based on location
Table it!
Weight
Mass
Changes based on
location
Measured in Newtons
Always stays the same
Tool: Spring scale or
digital scales
1N
Tool: balance or digital
scale
100g
Measured in Grams
How do they compare?
180 lbs on Earth
0 lbs in space
81 kg on Earth
81 kg in space
Which one??
Which weighs the most on Earth?
Which weighs the most in space?
This is NOT a new formula…
Gravitational Force = Weight
So if
then
where g = 9.8m/s2 and m = mass in grams
Spring Scale Practice (10 min.)
Background: have you ever jumped up and down
on a scale, what happens to your weight?
Objective: See how changing acceleration can
add or take weight away
Materials: (1) spring scale/group
(2) Weight, anything you can find
Review 1
How does the mass of an object relate to the
The larger
thethat
mass,
larger
theon
force
gravitational
force
thethe
object
exerts
vice versa.
other and
objects?
The gravitational force on Jupiter is
approximately 2.3 times the gravitational force
on Earth.
has a the
masssame)
of 70 kg
MassIf=an
70object
kg (stays
; and a
weight
of 686=N2.3
on Earth,
Weight
X 686what
N = would
1577.8the
N
object’s mass and weight on Jupiter be?
Review 2
How do you explain to someone who has
Gravity holds
the planets
in orbitexists
no knowledge
of gravity
that gravity
around the sun.
in space?
Why does your weight change if you
Weight
is a measure
ofmass
gravitational
landed
on Mars,
but your
does not?
force, while mass is constant
Gravity and Acceleration
Objects fall to the ground at the
same rate because the
acceleration due to gravity is
the same for all objects.
Check out these videos: http://www.youtube.com/watch?v=z_sJ15feNGw
and http://www.youtube.com/watch?v=aRhkQTQxm4w
How fast is it moving when it hits the
ground?
Acceleration Due
to Gravity…for
every second that
an object falls, the
object’s
downward
velocity increases
by 9.8 m/s.
Velocity of falling
objects formula:
∆v = g × t
Let’s Practice!
Terminal Velocity Check!!!
Check out these videos to review Terminal
Velocity:
http://www.youtube.com/watch?v=4qeCcv
q2_io
http://www.youtube.com/watch?v=V_wnJ8
4AFmI
OK…your turn…SUMMARIZE it!
Centripetal Acceleration
Centripetal acceleration is acceleration in a
circular motion; it is CONSTANTLY accelerating –
WHY??
It is CONSTANTLY changing direction!
Consider the example of swinging a cup of water
in a circle.
What happens?
Video:
http://www.youtube.com/watch?v=56QCI4Ig4EY
Orbiting and Centripetal Force
The unbalanced force that causes
objects to move in a circular path is
called a centripetal force.
Gravity provides the centripetal force
that keeps objects in orbit.
Free Fall
Free Fall Occurs When There Is No Air Resistance
An object is in free fall only if gravity is pulling it
down and no other forces are acting on it.
A vacuum is a place in which there is no matter.
Objects falling in a vacuum are in free fall because
there is no air resistance.
Free Fall on a ride:
http://www.youtube.com/watch?v=JzKZNm1lcDc
Projectile Motion
Projectile motion is the curved path an
object follows when it is thrown or
propelled near the surface of the Earth.
Projectile motion has two components—
horizontal motion and vertical motion.
These components are independent, so
they have no effect on each other.
Projectile Motion
Horizontal Motion
Horizontal Motion is a motion that is
parallel to the ground.
When you throw a ball, your hand
exerts a force on the ball that makes
the ball move forward. This force gives
the ball its horizontal motion.
Vertical Motion
Vertical Motion is motion that is
perpendicular to the ground.
A ball in your hand is prevented from
falling by your hand. After you throw
the ball, gravity pulls it downward and
gives the ball vertical motion.
Newton’s Hypothesis…
He hypothesized that the moon was simply a
projectile circling the Earth under the attraction
of gravity.
YOUR TURN AGAIN…SUMMARIZE IT!!
HOMEWORK!!! Answer in COMPLETE
sentences! EXIT TICKET!!
What is the acceleration due to gravity on Earth?
Why do all objects on Earth fall at the same
acceleration?
What are the 2 parts of the Universal Law of
Gravitation?
Compare Mass and Weight. UNITS too!
Formulas for calculating gravitational force and
velocity of a falling object.