Download Over head 2

Answer these questions…
1. Why doesn’t earth fly off into
space?
2. Where is Gondwanaland?
3. How do airplanes stay in the
sky?
4. How much do you weigh in a
pool of water?
Notes: Speed, Velocity and
Acceleration
How do you know if an object is in
motion?
• It’s distance from another object is changing
• The other object is the reference point ( a place
or object used for comparison to see if an object
is moving)
How do you describe motion?
• Distance – How far it goes (measured in
meters)
• Speed – How fast it goes
• Time – How long it takes to get there
• Formula for Speed = Distance/Time
• Example: 50 miles per hour
Constant Speed
• Constant Speed – When an object’s speed
is the same at all times during it’s motion
– Example – an ship traveling across the ocean
may move at the same speed for several
hours
– Long Distance Swimmers/Runners – keep the
same pace for a certain part of the race
– Practice Problem: A train travels at a constant
speed of 80 miles in 2 hours. What is it’s
speed?
Average Speed
• Most objects do not move at the same
speed for the entire time that it is in
motion.
– Example: A cyclist may glide over level
ground, climb slowly up a hill, speed down
hills
– Practice Problem: A car is driven 60 miles in
2 hours and 100 miles during 4 hours. What
is the car’s average speed?
Velocity
• Speed in a given direction
• Example – 4 meters per second North
• Who would use velocity in their careers?
• How would they use velocity?
Theory of Plate Tectonics
• Earth’s plates move in • Pangaea – super
various directions
continent
very slowly
• Laurasia – Northern
mass of super
continent
• Gondwanaland –
Southern mass of
super continent
http://pubs.usgs.gov/publications/text/historical.html
http://library.advanced.org/17701/high/pangaea/
Figure this one out…
• Suppose scientists discover
that a plate will move 5
centimeters per year.
• Can you predict how far the
plate will move in 1,000 years?
• How far will the plate move in
a day?
Alfred Wegener
(1880-1930)
Developed Theory
of Pangaea
Alexander du Toit
(1878-1948) Believed
that Pangaea broke
apart into 2 supercontinents – Laurasia
and Gondwanaland
Acceleration
• A change in
velocity -either
increasing speed,
decreasing speed
or changing
direction
• Acceleration =
• (Final Velocity –
Initial
Velocity)/Time
Figure this one out…
• A roller coaster picks up speed as
it rolls down a slope.
• As it starts down the slope it’s
speed is 4 meters/second, but 3
seconds later it’s speed is 22
meters/second.
• What is the average acceleration?
Explain This…
• When you travel in a
car, where do the
pushes and pulls you
feel come from?
• When you experience
pushes/pulls
associated with
acceleration, you
continue the motion
you had BEFORE the
acceleration began.
• Check out the go-kart
picture
To Make Motion Graphs Easier:
1. A straight line means constant speed.
2. A horizontal line means no motion, 0
speed.
3. A positively sloped line means motion
away from the reference point, + velocity
4. A negatively sloped line means motion
toward the reference point, - velocity
5. A steeper slope = faster speed.
To Make Motion Graphs Easier:
6. The value of the slope is defined
by the graphed units of time and
distance
7. A curved line means a change in
speed.
8. The rate of curvature defines the
amount of acceleration.
Demonstration
• What affects the acceleration of an object?
• Which student moves faster?
• Which student moves further?
• Which student stays in place?
Why did this happen?
• Objects with a larger mass have a
greater resistance to acceleration.
• Inertia – the tendency of an object to
resist changes in motion
• Force – a push or pull (sometimes
results in motion)
Demonstration – Penny Activity
• What will happen to the penny if
you YANK the card out from
under it?
Yikes!!!
Help Me!!
Why did this happen?
• What actually happened? You caused
the card to accelerate horizontally.
• Why did this happen? The force was
applied to the card only – Inertia kept
the coin from moving.
• Do you think it would be different if
you pulled it slowly? It should go with
the card everytime.
Who is Isaac Newton?
• An English
mathematician
that discovered
the three laws
of motion.
Newton’s First Law
• An object
remains in
motion or at
rest unless
acted on by a
force
Balanced vs. Unbalanced Force
• Balanced Forces
– all the forces
acting on an
object cancel
each other out
• Unbalanced
Forces – when
there is a
greater force in
some direction
causes
movement
Friction
• A force that resists
motion between two
objects in motion that
are touching
• Example – a
runner’s shoes and
the running surface
• Ice – not enough
friction
• Mud – too much
friction
• Example – air
hockey table
There are three
types of friction
Sliding Friction
• When two objects are rubbing against
each other
Rolling Friction
• The friction that exists when a
wheel turns on a surface.
• Caused by the small
indentations created as one
surface rolls over another
• Resists slipping and spinning
Fluid Friction
• The friction on a solid object as it moves
through a liquid or gas
Gravity
• A force that pulls free falling objects to
earth’s center
• All objects accelerate downward at a rate
of 9.8 m/s2 (meters/second squared)
Demonstration – Money, Money
• Do all objects fall at the same rate?
• Which would fall faster a book or a dollar
bill?
• Why?
• How can we get them to fall at the same
rate?
Why did this happen?
• As objects fall, more massive objects are
more attracted to the earth but are also
harder to accelerate (because of inertia)
• Their inertia reduces their acceleration by
exactly half as much as their greater
attraction increases it
What is the difference between
mass and weight?
• Mass – the
• Weight – the
amount of matter
gravitational
in an object
pull of an
• Greater mass =
object toward
greater inertia
the earth
• So mass= the
amount of inertia
in an object
Overhead 6
Newton’s 2nd and 3rd Law
Newton’s Second Law
• The force of an
• Force = Mass x
object is equal to
Acceleration
the product (think
• Force is
math – what is a
Measured in
product) of its
Newtons
acceleration and its
mass
• Mass – usually in
Kg
• Acceleration =
m/s2
Think about it…
• Since weight is a force you can
rewrite Newton’s second law:
• Weight = mass x acceleration
Newton’s Third Law
• For every action force there is an equal
and opposite reaction force.
Action vs. Reaction Force
• Action Force – a push
on something
• Reaction Force the force that
pushes back
• Example –
balloon, fire
hose, bullet fire,
passing gas in
the bath tub 
Newton’s Third Law Cont.
• How many objects is Newton talking about
in his third law?
• Can Action and Reaction forces be added
together?
• No
• Why or Why not? Because they are acting
on different objects
Examples
• Figure Skaters – one
skater pushes against
the other – both move
• Squid – pushes water
out - he moves
forward
BUT….
• Remember the roller chairs….
• Who moved further?
• Speed and amount of movement when 2
objects are in contact depends on mass.
Another Example
• If forces are equal in strength but in
opposite directions then they cancel each
other out.