Download Week #2 Notes

Week #2 Notes
Monday, October 17th
Reminder: Week #2 Vocabulary and notes are
Due on Friday, October 21st
Newton’s Second Law
Fancy Definition: an object acted on by an unbalanced
force will accelerate in the direction of the force
Math Plug n Chug: Acceleration = Force / Mass
Acceleration = m/s2
Force = Newtons
Mass = kilograms
Newton’s Second Law
Easy Definition: If you apply a force, the object will move
in the direction of the force
Example: if you kick a ball forward….it will move forward.
Draw it. Use it. Love it.
Newton’s Second Law can tell you
about changes in motion….using
everyone’s favorite: math! 
Question: If a 10N force acts on a 2kg object, what
acceleration does it give the object?

Step #1: Write the plug n chug (formula)

Step #2: Write the formula again, but replace with the actual
measurements

Step #3: Chug out the answer
Which 2 numbers can you plug in?
a = F/m
a = 10N / 2kg
a = 5 m/s2
Question: If a 10N force acts on a 2kg
object, what acceleration does it give the
object?
Friction
There are 3 kinds: Rolling,
static, and sliding
Rolling Friction
When a wheel rolls over a surface
The force is in the direction of the
way the wheel is rolling
Would I be
able to ride
my bike on
ice as good
as on
concrete?
Bike wheel is moving forward
The rolling friction is forward
Static Friction
The friction that keeps a stationary object from moving
Static Friction
keeps her
food in place
http://www.inmagine.com/tt062/tt0132042-photo
Why is her food not moving
around on her tray?
Sliding Friction
Happens when 2 surfaces slide past one another
Why is this player not moving in a
straight line at a constant speed?
Acceleration
Change in velocity divided by the amount of time required
for the change to occur
If the object changes speed, direction, or both  its
accelerating
Unit of measure: m/s2

If you calculate acceleration and the
answer is positive: the object is speeding
up

If you calculate acceleration and the
answer is negative: the object is slowing
down
Acceleration

Acceleration = (final speed – start speed)
time
Calculate Acceleration

When molecules collide with an object and
slows its motion
 Example: hand out the car window
 Example: parachuting
 Example: walking in hurricane winds

Air resistance is a type of friction
◦ Will be opposite of the direction of the object

Air resistance increases with speed
Air Resistance
Weight & Mass
They are not the same!
Weight is the force of gravity on an object
 On Earth, objects fall back to Earth with
the same acceleration: 9.8 m/s2

Weight = mass x acceleration due to gravity
For us its 9.8 m/s2
Weight