welcome to physics’s world_presentation_newton's second law
TRANSCRIPT
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The Meaning of
Force
Determining The
Net Force
Balance and
Unbalance Force
Type of Forces
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Force is pull/push upon anobject resulting from the
objects interaction with
another object
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Contact
Forces
Action-at-a-
Distance Forces
- Frictional
Force
- Normal Force
- Tension Force- Air Resistance
- Applied Force
- Spring Force
- Gravitational
Force- Magnetic Force
- Electrical Force
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Normal Force
Surface
Normal Force
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Pulling Force
motion
Frictonal Force
Surface
Static frictional force () = . N
Kinetic frictional force () = . N
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T1 T2
T3
T4
A
B
Surface
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Air resistanceforce
Weight force
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N S
NSNS
NS
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The table
pushes upwardson the book
Gravity pullsdownwards onthe book
The friction between thetable/book surfacesexcerts a leftwards forceupon the right ward-moving book
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10 N
10 N
40 N40 N
70 N
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Vertical (X axis)
Horizontal (Y axis)
+ =10 N -10 N 0
+40 N -40 N
= 0So, the net force is 70 N on the north-east
direction,
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The accelerat ion o f an ob ject as
produced by a net force is direct ly
propo r t ional to the magn i tude ofthe net force, in the same d irect ion
as the net fo rce, and inversely
propo r t ional to the mass of theobject.
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= a
= m a
F = Newton (N)
m = Kilogram (Kg)a = Acceleration
(m/)
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m
Fa
M
F
a
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= m .
= m .
= m .
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Acceleration have
same direction with
the net Force
Acceleration is
produced by the net
Force
The unbalanced
Forces cause objects
to accelerate
Draw the free-body
Diagram
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You push an object initially at rest, across africtionless floor with a constant force for a
time interval t, resulting in a final speed of v
for the object. You repeat the experiment but
with a force that is twice as large. What timeinterval is now required to reach the same
final speed v ?
a. 4 t
b. 2 tc. t
d. t
e.
1
4t
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Solution :
Acording to Newtons second law : = m a
a =
and
= m .
=
.
2=
.
1
2=
2=
1
2t (D)
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If you push a heavy box that is at rest, you
must exert some force to start it motion.
However, once the box is sliding, you can applya smaller force to maintain that motion. Why?
Answer :
To get the box to slide, you must pushharder than the maximum static frictional
force. Once the box is moving, you need to
push with a force equal to the kinetic
frictional force to maintain the boxsmotion.
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When two objects of unequal mass are hung
vertically over a frictionless pulley of
negligible mass, as figure below. Determine
the magnitude of the acceleration of the two
objects and the tension in the lightweight
cord!
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= (
+ ) gThus, we get :