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RECALL BACK,..

Do you still remember aboutNewtons Second Law of Motion?

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Newtons second law of motion

States that the acceleration of a body , is directly

proportional to the net force acting on it , and

Inversely proportional to its mass, .

m

m

FaaF

TTTT !! ,

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LETS WATCH THIS VIDEO,

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Why do

things falling

down?

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Learning outcomes;At the end of the lesson, a student

should be able to ;

explainanddeterminethe

value ofaccelerationduetogravity

Define gravitational fieldand

gravitational field strength

Define weightSolving problems involving

accelerationdueto gravity

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~Objects fall because they are pulled towards

the Earth by the force of gravity.

~This force is known as the pull of gravity or

the gravitational force.

~The gravitational force tends to pulleverything towards its centre.

falling

bodies

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IDEA OF GRAVITY

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1st Central guiding question

What is gravitational field and

gravitational field strength?

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Please look into these situation,..

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gravitational field

The region in which an object experiences a force

due to gravitational acceleration.

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Please draw the direction of gravitational force.

Force of gravity

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Gravitational field strength,

The force exerted on each kilogram mass by the gravitational field of a planet , star

or big mass

The gravitational force, per unit mass,

orThe unit

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Spring balance

Gravitational field strength, on earth = 9.8 Nkg -1

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What is the gravitational field strength in moon???

mass of the Moon = 7.36 1022 kilograms

mass of Earth = 5.9742 1024 kilograms

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What is the gravitational field strength in moon???

Only 1.6 kg N-1

Planet Mass (kg) g (N/kg)

Mercury 3.2 x 1023

3.61Venus 4.88 x1024 8.83

Mars 6.42 x 1023 3.75

Jupiter 1.901 x 1027 26.0

Saturn 5.68 x 1026 11.2

Uranus 8.68 x 1025 10.5

Neptune 1.03x 1026 13.3

Pluto 1.2 x 1022 0.61

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2nd Central guiding question

What is acceleration due to gravity?

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What are the forces that act on an object when the object fall?

Air resistance

Gravitational force

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Let do this activity.,.

Drop a piece of paper and a piece of compress paper from the same height

Which one will reach the ground first?

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How about if we fall the different

object in a situation without air

resistance??

Gravitational force

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Let do this activity.,.

Drop a ping pong ball and a marble from the same height

Which one will reach the ground first?

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FREEFALL

The falling of an object

that influenced by the

force of gravity only.

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The acceleration of an object caused by the gravitational pull

Acceleration due to gravity

The acceleration due to the gravity , g for the Earth = 9.8 ms-2

The net force acting on an object of mass, m in free fall,

From Newton Second Law , the acceleration of an object is given by :

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Planet Radius (m) Mass (kg) g (m/s2)

Mercury 2.43x 106 3.2 x 1023 3.61

Venus 6.073x 106 4.88 x1024 8.83

Mars 3.38 x 106

6.42 x 1023

3.75Jupiter 6.98 x 107 1.901 x 1027 26.0

Saturn 5.82 x 107 5.68 x 1026 11.2

Uranus 2.35 x 107 8.68 x 1025 10.5

Neptune 2.27 x 107 1.03x 1026 13.3

Pluto 1.15 x 106 1.2 x 1022 0.61

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3rd Central guiding question

What is the weight?

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What is your weight?

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WEIGHTThe gravitational force , , acting on a body

So, the unit of weight is Newton

Weight is a vector quantity

Weight = mass x gravitational field strength

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Weight

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scale scale scale

g = 9.81 N/kg g = 1.60 N/kg g = 26.6 N/kg

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Mass Weight

Themass ofan objectis

theamount ofmatterin

the object

The weight ofan object

the force of gravity

Constanteverywhere Varies withthemagnitude

of gravitational field

strength, g ofthelocation

A scalar quantity A vector quantity

A base quantity A derived quantity

SI unit: kg SI unit: Newton, N

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Question 1

_____ is themotion ofa body whenair

resistanceis negligibleandtheactioncan be

considereddueto gravityalone.

A) Free fall

B) Free flight

C) Negative fall

D) Zero-gravity fall

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Problems Solving

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QUESTION 2

A ballis thrown straightdown whileanother

oneis dropped bothatthe sameheight.

Neglecting airresistance , theacceleration just

before striking the ground

A. Greater forthethrown ball

B. Greater forthedropped ball

C. The same for both ball

D. Depends onhow highthey started

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QUESTION 3

Ifa boy weighs 500 N , whatis his mass?

A) 25 kgB) 51 kg

C) 500 kg

D) 4900 kg

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Learning outcomes;At the end of the lesson, a student

should be able to ;

explainanddeterminethe

value ofaccelerationdueto

gravity

Define gravitational fieldand

gravitational field strength

Define weightSolving problems involving

accelerationdueto gravity

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Let sing the song together,..

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FALSE

TRY AGAIN!!

4back

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TRUE

GOOD!!

Q1

Q2

Q3

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FALSE

TRY AGAIN!!

4back

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TRUE

GOOD!!

Q1

Q2

Q3

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FALSE

TRY AGAIN!!

4back

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TRUE

GOOD!!

Q1

Q2

Q3

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The end.

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