Force

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Force
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What is Force?
Force the push or pull of one object on
another Force is a vector quantity, therefore,
whenever calculating force, you must give --
an amount -- a unit -- a direction We very
often represent the direction of force with
arrows.
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Calculating Force
Force is a measure of how strong the push or pull
is on one object by another. Obviously, objects
with more mass push or pull stronger, so more
massive objects exert more force, However, force
isnt entirely based on mass alone, so using the
same units as mass is no good. -- Think about a
skinny guy and a fat guy and the force they exert
on a door. If the fat guy, with more mass,
slowly pushes the door, the door opens with
little force. But, if the skinny guy, with less
mass, charges into the door, the door will fly
open with lots of force. In the example above,
however, if both guys charge into the door with
the same speed, the door will be opened harder by
the more massive guy.
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Units for Force
Therefore, while mass is obviously a factor,
speed and acceleration also play a role in
calculating force When reporting force, we use
the units of Newtons (N) 1 N 1 kg m/s2 -- the
units for Newtons are derived from the formula
for force, which we will look at later -- YOU
MUST ALWAYS remember that mass must be in
kilograms (kg) when calculating force The unit
Newton, of course, is named for the famous
scientist Sir Isaac Newton, who spent much of his
time investigating forces
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Types of Forces
There are many different types of forces,
including -- Frictional force (how strong
friction is) -- Gravitational force (weight) --
Torque (perpendicular force) No matter what type
of force you are talking about acting on an
object, that force is either balanced or
unbalanced
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Balanced Forces
When all the forces acting upon an object are
equal in strength, but opposite in direction, we
say the forces are balanced -- the forces cancel
each other out and there is no net force -- net
force the sum total of all the forces acting
upon an object (remember this includes vector
quantities and therefore some forces must be
written as negative numbers) Example
7 N
7 N
Net Force 0
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Unbalanced Forces
When the forces acting upon an object are not
equal in strength, not in opposite directions, or
both, the forces are said to be unbalanced --
with unbalanced forces, there is a net force To
calculate unbalanced forces, we must add the
force vectors going in the same direction
together, and subtract all force vectors going in
the opposite direction Example 1 Example 2
3 N
5 N
2 N
7 N
Net Force
Net Force
10 N
3 N
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Force Practice Problems
1. 2. 3.
30 N
55 N
12 N
5 N
4 N
4 N
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Newtons First Law
Newtons First Law of Motion deals with the
effects of balanced and unbalanced forces.
(Newtons Laws are one of the main reasons that
the units for force are in Newtons) Wording of
Newtons First Law An object in motion will stay
in motion and an object at rest will stay at rest
unless an unbalanced force is acted upon it --
often called the law of inertia
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Inertia
Inertia is the tendency of objects to resist any
change in motion. The amount of inertia that an
object has is directly related to its mass --
the more massive an object is, the more inertia
that object has Basically, an object will move at
constant velocity unless an unbalanced force is
acted upon it -- remember that being stopped (a
constant velocity of 0 m/s) is a constant
velocity!!!
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Examples Of Inertia
Example 1 When youre riding in a car, and the
car slams on its brakes, your body keeps going
forward until a force acts upon it. Hopefully,
that force is the seat belt. Example
2 Demonstrations in the lab today with coins.
Even though the other coins/index cards moved,
the coin stayed still because no force was acted
upon it