Download Turbo Science

Turbo Science
for the “academically advanced“
(a.k.a. “really smart when they
apply themselves” students)
Turbo Topics
► The
following topics will be discussed this week
to give you some information (and hopefully
enough!) to prevent you from freaking out on
the CRCT test next week.
Disclaimer We will be moving at a warp speed this week, so I suggest you give me all of
your attention.
 The Big Kahuna (aka Mr. Crawford) has forbidden homework during testing- so I
have no way of knowing if you are keeping up with me!
Forcesfrictiongravityspeedvelocityacceleration and maybe
electricity!
Forces
► in
science it is defined as a push or a pull
► all forces have size and direction
► measured in newtons (N)
► net force- the combination of forces acting
on one object
 If net force = 0, then the forces are balanced
and there is no change in motion
unbalanced forces- produce a change in motion
Forces in the same direction
Forces in different directions
Friction
►a
force that opposes motion
► occurs when two surfaces are in contact
► amount of friction depends on two things:
 The force pushing the surfaces together
(increases contact)
 The texture or “roughness” of the surfaces
Types of Friction
kinetic friction – between moving objects
sliding friction – direct and maximum contact
ex. sliding a box across the floor
rolling friction - one object “rolls” over another
ex. using a cart with wheels to move the box
fluid friction – an object moves through a fluid
ex. moving parts of a machine
Friction: Good or Bad??
► Good!-
allows us to walk, cars to roll, cars
to stop and our pencils to write
► Bad!! holes in your socks, erosion of soil,
engine parts wear out
We can reduce friction by using lubricants,
smoothing the surfaces, using wheels or ball
bearings
Gravity
►A
force of attraction between two objects
due to their masses
► Law of Universal Gravitation- All objects in
the universe exert a gravitational force
(pull) on each other
 The size of the gravitational force depends on
the mass of the objects and the distance
between them
How Mass affects Gravity
How Distance affects Gravity
Weight and Gravity
► Weight
is a measure of the gravitational
force on an object
► Weight is measured in newtons (N)
► Weight is related to mass, but it is not the
same!
A small apple
weighs about 1 N
Mass vs. Weight
► definition
► tool
used to measure
► units
Make sure you know
this!
Motion
► An
object is in motion if it changes position
over time
 You must have a reference point!
We can tell the balloon is
in motion because its
position has changed with
reference to the
mountain.
Measuring Motion
Speed is the distance an object travels in a
certain amount of time
S = D/T
Example - 60 miles per hour (60 mph)
5 meters per second (5 m/s)
Average speed- total distance/total time
*because speed is usually not constant
Try It!
► Kara
jogs to the store 72m away in a time
of 36 seconds. What is Kara’s average
speed?
► An
airplane traveling from San Francisco to
Chicago travels 1,260 km in 3.5 hours.
What is the plane’s average speed?
Graphing Speed
Velocity
► The
speed of an object in a certain direction
► Velocity must include direction!!
► Ex.
60 mph east
5 m/s north
► Velocity
changes if either
speed or direction changes
Acceleration
► The
rate at which velocity changes over
time
► Acceleration occurs if:
 speed changes
►
►
speed up- positive acceleration
slow down – negative acceleration or deceleration
OR
 direction changes
Yes? or No?
► You
ride your bike around a track at a
constant speed of 11 km/h
► You ride your bike at 9 km/h and ten
minutes later your speed is 6 km/h
► You pedal faster to pass another bicyclist in
the race
► You ride your bike in a straight line at a
constant speed of 10 km/h
► Acceleration
is how quickly velocity changes
This biker is accelerating at 1 m/s2
For each second that passes, he speeds up by 1
m/s
Try It!
► An
eagle accelerates from 15 m/s to 22 m/s in 4
seconds. What is the eagle’s average
acceleration?
►A
car advertisement states that a certain car can
accelerate from rest to 90 km/h in 9 seconds.
What is the car’s average acceleration?
Graphing Acceleration
Acceleration due to Gravity
► Objects
fall due to gravity
If you drop a baseball and a ping pong ball at
the same time, which will hit the ground
first?
► Aristotle
said the baseball would.
► Galileo proved him wrong!
► Acceleration
depends on the mass of an
object and the force (gravity) acting on it.
 There is a trade-off between mass and force
The extra mass of the baseball balances the
additional gravitational pull needed to
accelerate the ball.
This stop action photo shows
that a ping pong ball and a golf
ball fall at the same rate even
though they have different
masses.
Acceleration due to
gravity is 9.8 m/s2
All objects accelerate toward
Earth at this rate- for every
second an object falls, it’s
velocity increases by 9.8 m/s
The balls move faster and travel farther in each
second than it did in the second before.
► If
a feather and an apple are dropped from
the same height at the same time, which
will hit the ground first?
► The
apple will hit first!
► The feather has more air resistance- a force
that opposes the motion of objects in air.
 There is more surface area on a feather that will
create friction with the air molecules
This is why we like to have a parachute
that opens when we jump out of the plane!
► As
the speed of an object increases, the air
resistance increases.
► Eventually air resistance (upward force) will
equal the force of gravity (downward force)
► Acceleration stops at terminal velocity
► From then on, the object falls at a constant
velocity
What if there is no air resistance?
In a vacuum, a
feather and an apple
will fall at the same
rate
The only force acting
on the object is
gravity - free fall
Free Fall
► Occurs
when there is no other force acting
on a falling object except gravity
► Free
fall can only occur where there is no air
(outer space or a vacuum)