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Friday PS Forces Part 2
Fundamental ideas
Balanced forces on an object will NOT
cause the object to change its motion
• Change of motion is caused by an
imbalance of forces in opposite directions
• Forces come in many types, including
contact, gravitational, and frictional forces
Friction
• Under-acknowledged about how important
it is to the normalcy of your life
In-class assignment
• Imagine you in a happy place doing something
that involves you moving
• Please keep it “G” or “PG” rated
• What would change if there was no friction?
– Think of your actions
– Think of your surrounding environment
– Think of your personal being
Assignment
• List at least 5 things/actions that would result
from no friction.
• They could be new actions/circumstances
• They could be alterations of old
actions/circumstances
• Write your response in a paragraph or two.
– Use full sentences.
– Introduction and closing sentences ARE REQUIRED
Friciton
• Force applied opposite to the direction of
motion Applied force
Friction force
• Amount of force depends on:
– The roughness of the surfaces being put
together
– The force used to push surfaces together
How does friction effect your live?
• Harmful friction
– Friction between moving parts
• Helpful friction
– Grip of tires on road
Friction involved with your mousetrap
Relationship between motion and
Forces
• Newton clearly stated the relationship in
his 3 laws of motion
• I expect you to be able to recite and
understand these laws completely
Rolling Ball
Newton’s first law
• An object at rest stays at rest
or an object in motion stays in motion
UNLESS
acted upon by a net outside force
Newton
Mass
• The amount of material located in an
object
• The amount of stuff that makes up an
object
Inertia
• The resistance of an object to change of
motion
• The more massive an object, the more
inertia it possesses
Newton’s 2nd law
• If there is a net force on an object, then
the object will accelerate
• The amount of acceleration depends on
the following relationship:
A = Fnet
m
• An object will gain more acceleration as
more force is applied
• An object will gain less acceleration if
more mass is added to it
Homework
• Read 331-332, 346-351
• Practice questions 1-3 on p351
Cars
• If you like it and its in good shape, either:
– Keep it and take it home
– With my permission, leave it on window ledges
If you don’t want it and it is not to be kept,
DISSASSEMBLE It!
Throw eye-screws, clean axles, wheels, spools into the
box
Grades
• Review to see if you are missing anything!