Transcript Forces and Motion…

Forces and Motion…
Everyday pushes and pulls
(that we never think about)
Everyday Forces
Forces
Gravitation
Magnetism
Friction
Which two forces have we studied this year?
Gravity:
the pull between all objects (the
greater the mass, the harder the pull!!!)

Discovered by Sir Isaac Newton
when an apple fell upon his
head…
Friction: causes motion to slow down or stop… causes drag!
Friction keeps us
from sliding off
the skateboard.
The tread on our shoes causes
friction, and keeps us from ending
up like this guy on icy roads.
The rough surface of the
mountain causes friction and gives
us a grip on the side of the
mountain when we rock climb.
Balanced forces are equal in size and opposite in
direction.
When forces are balanced, no change in motion occurs.
When forces are unbalanced, a change in motion occurs.
How can I tell when motion is occurring???
I need to know an object’s starting position to be
able to tell it has moved over a distance!
Distance
Speed: How long it takes to travel a given
distance

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Formula: Distance/Time = Speed
Ex: 55 miles/1 hour = 55 miles per hour
Time = 1 hour
Distance = 55 miles
Graphing Speed:
Distance vs. Time Graph
Denver
Phoenix
Question:
Below is a distance vs. time graph for 3
runners. Who is the fastest?
Leroy is the fastest. He completed the race in 3 hours.
How fast something looks like it’s moving all
depends on your frame of reference .
Velocity: The speed of an object in a
particular direction.
 Example:
 An
airplane moving North at 500 mph
 A missile moving towards you at 200 m/s
Question:
What is the difference between speed
and velocity?
Speed is just distance/time. Velocity includes
direction as well.
The rate at which velocity changes is called
acceleration.
It can be:
• an increase in speed
• a decrease in speed
• a change in direction
When an object’s motion
changes by slowing
down, we call this
deceleration.
Question:
How can a car be accelerating if its speed
is a constant 65 km/h?
If it is changing directions it is accelerating
Momentum: How hard it is to start or stop an object.
The more mass an object
has, the more momentum
it has.
Ex: It’s harder to stop a 200 lb.
linebacker than a 100 lb.
ballerina
The faster an object is moving, the more momentum it has.
Ex: It’s harder to stop a car going 50 miles an hour than a car going
10 miles an hour.
Newton’s Laws of Motion
Inertia: An object
Acceleration: The
in motion tends to
Equal and
stay in motion and an greater the mass of Opposite: For every
object at rest tends to an object, the greater action, there is an
the force needed to equal and opposite
stay at rest unless
cause a change in its
acted upon by an
reaction.
motion.
outside force.
Ex: Kicking a soccer
Basically, objects
ball makes it move. Ex: You and a friend
tend to keep doing
jumping on a
Kicking a bowling
what they’re doing!
trampoline!
ball just hurts
Ex: Seatbelt!!!