Transcript Forces are a

Q: What is Force?
• A: Force is anything that causes
acceleration. (All accelerations are
caused by forces)
– Main Principal #4: Objects move, or change motion, because of
forces acting upon them!
– If an object is stationary, it won’t start moving
without a force!
– Forces are a “Push” or a “Pull”
What we already learned…
Makes straight lines on graphs
Dis tance [m]
Velocity 
Time [ s]
Makes curved lines on graphs
Velocity [m]
Acceleration 
2
Time [ s ]
So what is the formula for Force?
First we had to know the acceleration formula:
Velocity [m]
Acceleration 
2
Time [ s ]
We have already covered what acceleration is in our last lesson;
Q: But what exactly is Mass? Good question! Go to the next slide:
Force  mass  acceleration
[kg m]
N
2
[s ]
“Newton” (N) is the unit of measurement for Force
So a push could be with a force of (for example) 45 N
Q: So What is Mass?
• A: Mass is the amount of “Matter” – or
“stuff” an object has.
– “Stuff” is made up of all of the
atoms/molecules that make up the object.
Objects with mass don’t just
suddenly start moving
by themselves
If it’s already moving, it takes
effort to stop it from moving!
An object with mass takes
some effort to move!
Because of the amount of effort
It can take to move something, it
almost feels like the objects “resists”
being moved at all!
We call an objects “resistance to
change in movement”: “Inertia”
So…the more mass something has, the more
Thinkforce
about
“Inertia”
like
this:
is needed to move it!
Ok, that
the object
toinSTART
moving.
Again,was
Inertia for
is: an getting
objects “resistance
to a change”
its current motion.
But what about stopping when it’s already moving?
Aifcar
a “heavy”
Butcarwith
object
enough
due
force
What
now,is
a nice
heavy
is
coming
right at
YOU? (hard
What kind
of to
force
be needed
to stop
it before
runsmove!
you over?
itswould
large
amount
enough
ofpush)
mass.
it itwill
It is quite
obvious that
is hard to push
You have
to “overcome”
theitinertia
a car
from for
a stationary
of the car
in order
it to moveposition
Man
Ok, trying
this
is but I
again,
heavy!
will push
harder!
Think: what would be required to move the car if it was a much bigger car?
Think: what would be required to move the car if it was a much smaller car?
Newton’s First Law of Motion:
• Also know as: Law of Inertia!
– Inertia is an objects resistance to a change in
its motion (even if it isn’t moving at all!)
– Inertia is caused because objects have mass
– The more mass an object has, the more
inertia!
– “An object at rest will stay at rest unless it is
acted upon by an outside force.” (and the opposite
is also true! An object in motion will stay in…blah blah blah)
What do you think happens to our
acceleration w/ different masses?
Distance
With less mass, it doesn’t take as
much effort to get it moving;
therefore, I can move it farther in
less time (faster).
½ kg
1kg
Less Mass =
less force
needed
2kg
With more mass, it takes more
effort to get it moving; therefore,
it takes me more time to move it
farther (slower).
Time
More Mass =
more force
needed
What do you think happens to our
acceleration w/ different masses if we
pushed with the same amount of force?
Distance
Which one of these lines do you
think would represent a sports
car? SUV, Diesel Truck?
The Diesel truck would be the least steep line!
Less steep = less velocity!!!
Sports car would be the steepest line!
Steeper = more velocity!!!
The SUV would be the middle line!
Steepness of line is in the
middle = middle velocity
Time