kaharuddin 04 1329040026

RESUME BUKU FISIKA

HUKUM NEWTON

oleh :

KAHARUDDIN

1329040026

KELAS ICP 04

PRODI PENDIDIKAN TEKNIK INFORMATIKA DAN KOMPUTER

JURUSAN PENDIDIKAN TEKNIK ELEKTRO

UNIVERSITAS NEGERI MAKASSAR

2013

Kaharuddin-1329040026 | ICP PTIK 04 UNM 2013

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INTRODUCTION OF FORCE

Force is a quantity that cause an object could move. Force cause the change of

an object, that’s changing of shape, characteristic of object moving, velocity, and

direction of object moving. In other side, force is not always cause a move. For

example, if we force a wall with the big power, but the wall still silent or not move.

A force has value and direction, so it’s a vector which follow the regulation of

vector sum. To measure value or power of force, we can use a spring balance.

LAWS OF NEWTON

Laws of newton discussed about relation between object movement and force.

Here, we will re-analyze three of newton’s laws and apply it to simple problems

about dynamic.

1. Newton First Law

At the past era, people believes that this world is moving by its self.

Nothing move it, so they said it Natural Movement. In other side, the object that

moving distinctly, they said it a forced moving. This theory was announced by

Aristoteles has the mistakes when Galileo and Newton suggest their argument.

Galileo breaking Aristoteles’s theory with a simple experiment. He make

a curve smooth line that used to wheel a ball. He makes a different slopeof a side

of that line. Observed, Galileo said “if friction force of that object was ignored, so

it object will always move without need a force again”

Galileo theory expanded by Icsaac Newton. Newton said that “if force

resultant of an object is zero, so the motionless object will keeping do that and

moving object will keep its movement with a konstant velocity”. That Newton’s

conclution knowing as Newton First Law. Mathematically can be defined :

∑ 𝐹 = 0


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Depend on Newton’s theory, This law also called as law ow inertia. Inertia

size quantity of an object is mass. Every object has differents inertia. The more

big mass of an object, the more of its inertia. We did newton first law everyday .

forexample, when our vehicle is suddenly braked. So we will pushed to the front

and if the vehicle suddenly move, we will pushed to the back.

2. Newton Second Law

Newton first law only discussed about object that is not influenced force from

outside, it means that object is not doing an acceleration.

Suppose we push a box on the

slippery floor (friction ignored) with

F force, but reality it resulting an

acceleration of a. When the push

force against the box increased twice

from original (2F). Reality it resulting

an acceleration twice from original

(2A). And when we increase push

force again becomes three times from

original (3F), In the fact, the result of

acceleration becomes three times of

original (3a)

So, it can be concluded that the

acceleration is proportional to the

magnitude of the resultant force on an

object (a ~ f)

Also can be concluded that the acceleration is inversely proportional to the

mass of the object(𝛼 ~ 1

𝑚).


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Depend on by both of that conclusion, Newton merge it become a statement

that knowing as Newton Second Law, that’s “Acceleration that produced from

resultant of the force that work directly proportional with force resultant, and

inversely with the mass of the object. Mathematically can be defined as:

3. Newton Third Law

Newton said that, Force that work on an object always comes from other object. It

means none of the force that only involve single object. The come force at least need

two objects interact each other. On this interact the forces always pairs. If A do a

force to B (action), so B will do a force to A (reaction). This pair of force knowing as

action-reaction pairs.

Before, we already know that the forces of action and reaction magnitude equal

but has opposite direction. Pairs of this action an reaction explained by newton on his

third law. Newton third law sound as “if an A object do a force on B object, so B

object will do a force on A object, that forces of action and reaction magnitude equal

but has opposite direction.

This law usually mentioned as “for every action, there is a reaction that equals

but has the different direction”. Mathematically this law can be defined as:

Faction = Freaction

Information:

𝑎 : Acceleration of the object (ms-2)

∑ 𝐹 : Resultant of force that work on the object (N)

m : Mass of the object (kg)


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TYPES OF FORCE

Force is a pull or push which will increase or decrease movement of an

object.

A. Weight Force

In our daily life, some of people misspresented between mass and

weight. Mass and weight has the different meaning. Mass is the size of

amount material contained of an object. The value of mass (m) of an

object always has the same value wherever it stand, and the unit is kg.

Weight (w) is the force of gravity worked on an object. Units of weight is

Newton (N).

Mathematically can be defined as :

w = m x g

w : weight (N)

m : mass of an object (kg)

g : gravity (ms-1)

B. Normal Force

Normal Force is the force that work on a field that touched

between two object surfaces, the direction always perpendicular with

touched field. On an object there is two force worked, that’s Normal

Force (N) that comes from working object and Weight Force (w). Both of

that force has the same value but has the different direction, so they make

a bance on an object.

C. Friction Force

Friction Force is force worked between two surface of a touched

object. Direction of friction opposite to the direction of tendencies object.

For the moving object on the air, its friction depends on the area of

surface that contact with air. How big the area of touched surface,

automatically how big the friction of its object while for solid object its

friction depend on area of touched field


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Friction force can be separated in two kinds, that’s static friction

(fs) and kinetic friction (fk). Static friction is the friction force that work

during its object still silent. Depend on Newton First Law, if force

resultant of an object is zero, so the motionless object will keeping do

that and moving object will keep its movement with a konstant velocity.

So, during the object still silent the static friction always same with the

force that worked in its object. Mathematically can be defined as:

Kinetic friction (fk) is the friction that work on moving object.

This force include on dissipative force, that is force which changing the

work to the heat. Comparison between kinetic friction and normal force

called coefficient kinetic force (ms). Mathematically can be defined as:

Information:

fs : the maximum static friction force

µs : coefficient static friction

Information:

Fk : the maximum kinetic friction force

µk : coefficient kinetic friction


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We have known that the object which do a uniform circular motion also will

doing centripetal acceleration. Direction of centripetal acceleration always towards

to the center of the circle and perpendicular with velocity of vector. Newton second

law said that force is multiplication between mass of object and acceleration that

experienced by that object. Mathematically can be defined as:

Information:

Fs : Centripetal force (N)

m : mass of object (kg)

v : linear velocity (m/s)

r : radius of circle (m)

w : angular velocity


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APPLICATION OF NEWTON’S LAW

1. Movement of plane

Object (a) is stand on smooth object pulled horizontally by force F. and it

moving with an acceleration a. because move on x axis (horizontal), so the worked

force on this object can be defined as:

Different with object (a), object (b) pulled by force (F) make an angle. The

component caused this object move on a smooth plane is horizontal component

F,that’s Fx. therefore mathematically can be defined as:

Depend on newton second law, the acceleration of this object is:


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2. Movement of two contact object.

Mathematically can be defined as:

So the equation of contact force between two object is:

3. Movement of oblique object

The forces that work on Y axis is:


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While, the force that work on x axis is:

Acceleration of the object can be defined as:

4. Movement of the object that using pulley

Depend on Ma object:

Depend on Mb object:


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Because we suppose that rope is massless and pulley is smooth, so the friction

between pulley and rope is ignored. So, the rope tension of both rope is same.

Therefore, the equations above can be simplified becomes:

5. Leg press force on the lift

The force of leg press can be defined by


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6. Motion of concerning on the road

Depend on X axis (horizontal)

Depend on Y axis (vertical)

If we substitute the equations above, we will found an equation like:


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7. Movement of vertical circle

Mathematically the equation is:


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EXAMPLE

1. A truck can make a force about 7.000 N. If the truck can move with

acceleration about 3,5 m/s, determine the mass of that truck!

Given :

a. ∑ 𝐹 : 7.000 N

b. 𝑎 : 3,5 m/s

Asked :

m : ..?

Answer :

So, the mass of that truck is 2 ton

2. An Ice box has 25 kg mass pushed by Raffi with angle about 300. If the

ice box move with the constant acceleration about 1

4 √3 m/s2, so the force

done by Raffi is ?

Given :

a. m : 25 kg

b. a : 1

4 √3 m/s2

c. α : 30o

Asked :

F…..?


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Answer :

So, Raffi push the ice box with the force about 123,5N.

3. There is two touched object sttart with silent on the smooth floor (look

object below). If the first object make a force about 200N, so determine

the acceleration and Contact force of each object .

Given :

a. ma : 70 Kg

b. mb : 30 kg

c. F : 200N

Asked :

a. a = ..?


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Answer :

a. Acceleration of the object

b. Contact force between each object

4. A beam has mass about 6 kg slide to the bottom on a smooth board which

inclined 30O from the floor. The distance of floor and beam 10 m and the

gravity is 10ms-2, determine acceleration and time needed by beam to get

the floor.!

Given:

a. m : 6 kg

b. s : 10 m

c. α : 30O

d. g : 10ms-2

Asked:

a. a :….?

b. t : ….?


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Answer:

a. depend on Newton second law

F= m x a

w sin 300 = m x a

m x g sin 300 = m x a

6 x 10 x 0,5 = 6a

a = 30

6 = 5ms-2


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b. Depend on GLBB

5. Look at the picture.!

Asked :

a. a ….?

b. T =…?

Given :

m1 : 5 kg

m2 : 10 kg

g : 10 ms-2


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Answer:

a. Because ma > mb so,

Substituted (1) and (2) becomes

b. T is

First object :

Second object :

6. A driver will pass a street corner radius 80 m with a slope angle of

37 °. If the force of gravity 10 ms-2, then how the driver specify the

maximum speed in order not to slipping off the track?

Given :

a. r : 80 m

b. 𝜃 : 370

Asked :

v =… ?


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Answer :

7. Faisal vertically rotate a bucket of water with radius of 0.8 m. If the

gravitational force of 9.8 ms-2, then specify minimum speed of the water

in the bucket so that it does not spill!

Given:

Asked:

Answer:

8. A Force 40N given to a silent beam on a smooth horizontal surface (mass

of beam is 20 kg). Determine the acceleration of the beam.

Given :

a. F = 40 N

b. m = 20 kg

Asked :

a...?


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Answer :

a = ∑ 𝐹

𝑚 =

40 𝑁

20 𝑘𝑔= 2 m/s2

9. Mass of a beam is 20 kg placed on the sloped field which make angle

about 500 toward horizontal. (there is no other force worked on the

beam). Determine the acceleration of that object.!

Given :

∑ 𝐹= mg sin α

g : 9,8 x 10 ms-2

sin 500 : 0,7

Asked :

a.....?

Answer:

a = ∑ 𝐹

𝑚 =

𝑚𝑔 sin 50

𝑚 = g sin 500 = 9,8 x 0,7 = 7,5 ms-2

10. A beam move on a oblique surface which make an angle 𝜃 = 150. The

beam move from the high of oblique place. Length of the oblique surface

is 2 m. Determine acceleration of that beam.!

Given :

mg sin 𝜃 : ma

a : gsin 𝜃

g : 10 m/s-2

sin 150 : 0.25

Asked :

a : ...?

Answer :

mg sin 𝜃 : ma

a : gsin 𝜃

a : 10 x 0.25

a : 2.5 m/s2


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Fisika

Untuk SMA/MA Kelas X

Disusun oleh : Joko Sumarsono

Editor : Diyah Nuraini

Design Cover : Desteka

Setting/Layout : Ike Marsanti, Esti Pertiwi

Penerbit CV Teguh Karya

Tahun 2008

kaharuddin 04 1329040026

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