The Physic’s
FORCE (GAYA)
Please find define about :
a)
b)
c)
d)
e)
f)
g)
h)
Force “ Newton’s Law” (Law I, II, III)
Expression of Force
Kind Force and explain!
Formula to find of Force
Resultant of Force
Advantage and Disadvantage of Friction Force (Gaya Gesek)
Different between mass and weight
Compare mass and weight, in “Pole” place and “Equator” place
a) Force . . .
Is pull or push for same substance.
The device used to measure force is Spring Balance or
Dynamometer.
In International System (MKS) the unit of force is Newton
or Abbreviated N.
1 N = 1 Kg m/s2
In CGS System the force unit is Dyne.
1 Dyne = 1 g cm/s2
Relationship of Newton and Dyne are as follows:
1 N = 105 dyne
Or
1 Dyne = 10-5 N
Force is given symbol F which come from the word force.
1) Newton’s I Law
If you ever ride a vehicle such as car or bus, when the
vehicle you ride suddenly move from the rest, your
body will be pulled backward or when that vehicle is
running fast suddenly is braked, your body will be
pulled in front.
Why does that happen?
The property to stand self condition is called as
Inertia. This inertia phenomena by Newton is applied
as inertia law or Newton’s I Law. Newton’s I Law :
“Every body will be at rest or moves in uniform
rectilinear if there is no force change that
condition.”
Or in other words
“ If force resultant acting on the body is
equal to zero, or there is not force acting on
the body, the body will be at rest (does not
move) or will move in uniform rectilinear.”
So in Newton’s I Law hold :
a) Every body at rest has inclination to stand its rest condition.
b) Every moving body, has inclination to stand is motion.
Newton’s I Law is formulated as follow :
ΣF=0
Which mean force resultant on the body is equal to zero.
Several example of application of Newton’s I Law in every day life
among other are as follow:
☺ Someone goes down from moving but will follow direction of
bus motion.
☺ Show of a motorcycle rider which can lift back wheel of his
motorcycle by
breaking front wheel suddenly when the
motorcycle is running.
2) Newton’s II Law
When you push the empty cart with small force, the
cart will move fast. But, when the cart is loaded fully
with heavy enough goods, so the full cart will move
slowing. For the cart move faster you must add force
on the cart.
From that phenomena can be concluded that motion of
a body is influenced by force and mass of the body.
The larger mass of the body, the acceleration of the
body is larger.
Relationship between acceleration, force, and mass of
the body is first provided by Newton. The statement
he provided is known as Newton’s II Law. While
content of Newton’s II Law is as follow:
“The body that influence force will have
acceleration which its magnitude is directly
proportional to the magnitude of the sum of
force and inversely proportional to its mass.”
Mathematically, Newton’s II Law is formulated as follow:
a = F/m or F = ma
In which:
F = The force acting on the body.
m = Mass of the body.
a = Acceleration of the body.
Several application of Newton’s II Law in daily day life among other
are as follow:
☺ The striking car will be easily pushed by two men, compared
pushed by one men.
☺ Golf ball is hit hard will move faster compared with golf ball
which is hit slowly.
☺ Body will have weight.
☺ Body will be influence by Earth gravitational force.
3) Newton’s III Law
If you play skateboard, for the skateboard can go
forward then you must press on of your feet to the
road while another on stays on the skateboard.
The pressure of your feet makes action force on the
road while road makes reaction force in opposite
direction with direction force of your feet. So the
skateboard you ride will go forward.
The phenomenon shows application of Newton’s III
Law. While the connect of Newton’s III Law is as
follow:
“If a body makes force (making action) to another
body, appears reaction force from the body to the
former body with equal magnitudes, while the
direction are in opposite.”
So, in Newton’s III Law hold the following things :
☺
☺
☺
☺
There are two force acting on two bodies.
Those two force have equal magnitudes.
Those two force have opposite direction.
There is action force which is equal to reaction force.
Mathematically, Newton’s III Law is formulated as follow
Faction = -Reaction or F1 = -F2
In which
F1 = Action force
F2 = Reaction force
The sign (-) shows those two forces are in opposite direction.
b) Expression of Force
Force is expressed by Vector.
A force has value and direction because the force is a
vector quantity. The force can be drawn by using a vector
diagram in the form of an arrow, as the figure below.
A
The Vector Diagram
B
The point A is called point of application of the force. The
direction force is represented by direction of arrow, while
the magnitude of force is represented by the length of
arrow, namely the length of AB.
For example the force 30 Newton’s rightward.
F = 30N
c) Kind Force and explain!
∞ Contract Force:
1) Muscular Force
Is force that comes from muscular power. Muscular
force can be done by organism such as animal and human.
By the muscular force someone can do work or
activity, such as pushing, pulling, lifting, hitting, kicking, and
so on.
Example: A mother is bringing her bag by using force
from her arm muscles.
2) Machine
Is the force generated by a given the machine.
Human often use the aid of machine, for instance to lift
heavy bodies.
3) Spring
Is forces that produce from a spring, because the
spring is pulled or pressed.
Example: A catapult use to throw a small stone by
placing the small stone in the edge of catapult, rubber of
catapult is pulled then it is release, so the stone will be
thrown.
4) Frictional
Is a force produced because of the presence of
relative friction between two bodies surface.
The influence of frictional force can be observed at the
ball rolled on the flat ground, sometime obviously the ball
stops without something stopping it.
∞ Non Contract Force:
1) Electric
Is a force produced by electrical charged
Example: A plastic comb can attract the pieces of
small paper. Before that plastic comb is wiped to the hair.
2) Magnetic
Is a force produced by magnets
Example: Is iron filings can be attracted by a bar
magnet.
3) Gravitational
Is the attract ional force caused by the Earth. The
things we throw upward will always fall the Earth. This
happen because of the presence of gravitational force.
Example: Ball thrown to the will down to the ground.
d) Formula to find of Force
a = F/m or F = ma
Or
e) Resultant of Force
In fact, that force acting on the body can be mare
than one. Besides the force acting on the body in one work
line can be directional or opposite. So the force acting on
the body can be the sum or different of the force.
Several force acting on the body in one work line can
be replaced a force called force resultant.
F1
F3
F2
On the body work three force F1, F2, and F3
Mathematically, the
expressed as follows.
magnitude of
force
resultant
(R)
is
R = F1 + F2 + F3 + . . .
To simplify calculation, give positive sign (+) for the
force directed to the right upward and negative sign (-)
for the force directed to the left or down ward.
f) Advantage and Disadvantage of Friction Force
(Gaya Gesek)
Advantage:
a. Frictional force between feet and the surface of
floor/road cause we can walk.
b. Frictional force between parachute and air cause
the parachutist can fly on the air and fall slowly.
c. Breaking system in a vehicle to retard/stop the
vehicle.
d. Frictional force between car tires which is made
serrated so can grasp road surface so the car is
not slipped.
Disadvantage:
a. Frictional force between car/motorcycle tires and
road cause car/motorcycle tires are quickly thin.
b. Frictional force between piston and cylinder in car
engine so the engine hot quickly which cause it
timeworn quickly.
c. Frictional force between air and the body of the
motorcycle rider, causes the motion seems the
motorcycle retarded.
d. The base of sandal and shoe become thin because
often in fraction with the road.
g) Different between mass and weight
Mass
a) Mass is amount of
substance in the
matter.
b) Scalar quantity has
value but not have
Weight
a) Weight that influence by
acceleration gravitational.
b) Vector quantity has value
and direction.
c) According with place.
direction.
c) Fixed at anywhere.
d) Unit = Kg
e) Measuring tool =
Balance.
d) Unit = Newton
e) Measuring tool = Spring
Balance.
h) Compare mass and weight, in “Pole” place and
“Equator” place
The pole vault is all about energy and energy storage. Lifting a person
upward takes energy because there is an energy associated with
altitude—gravitational potential energy. Lifting a person 5 or 6 meters
upward takes a considerable amount of energy and that energy has to
come from somewhere. In the case of a pole-vaulter, most of the
lifting energy comes from the pole. But the pole also had to get the
energy from somewhere and that somewhere is the vaulter himself.
Here is the story as it unfolds:
When the pole-vaulter stands ready to begin his jump, he is motionless
on the ground and he has no kinetic energy (energy of motion), minimal
gravitational potential energy (energy of height), and no elastic energy
in his pole. All he has is chemical potential energy in his body, energy
that he got by eating food. Now he begins to run down the path toward
the jump. As he does so, he converts chemical potential energy into
kinetic energy. By the time he plants his pole at the jump, his kinetic
energy is quite large.
But once he plants the pole, the pole begins to bend. As it does, he
slows down and his kinetic energy is partially transferred to the pole,
where it becomes elastic potential energy. The pole then begins to lift
the vaulter upward, returning its stored energy to him as gravitational
potential energy. By the time the vaulter clears the bar, 5 or 6 meters
above the ground, almost all of the energy in the situation is in the
form of gravitational potential energy. The vaulter has only just enough
kinetic energy to carry him past the bar before he falls. On his way
down, his gravitational potential energy becomes kinetic energy and he
hits the pit at high speed. The pit's padding extracts his kinetic
energy from him gently and converts that energy into thermal energy.
This thermal energy then floats off into the air as heat.
One interesting point about jumping technique involves body shape. The
vaulter bends his body as he passes over the bar so that his average
height (his center of gravity) never actually gets above the bar. Since
his gravitational potential energy depends on his average height, rather
than the height of his highest part, this technique allows him to use
less overall energy to clear the bar.