Projectile Motion Part 1| Grade 9 Science Quarter 4 Week 1 Lesson

good day students welcome back to ma

estrang techie youtube channel we are

now in quarter four of our grade nine

science lesson and the first topic that

we are going to have today is all about

the horizontal and vertical motions of a

projectile check out our learning

objective describe the horizontal and

vertical motions of a projectile get

ready to learn this lesson so keep on

watching

[Music]

in grade 8 you have learned about

newton's second law of motion the law of

acceleration according to these law the

net force is equal to the product of the

mass of the object and its acceleration

let's have a simple activity to refresh

your mind state the second law of motion

by completing this paragraph

so let us start the law of

of course

acceleration the acceleration of an

object as produced by a net force is

directly proportional to the magnitude

of the net force

in

the same direction as the net force

and

inversely proportional to the

mass of the object that is the second

law of motion

good job class it is very good that you

can still recall the law of acceleration

always remember that the larger the

force applied on an object the larger

its acceleration usually the

acceleration of a body may change and

vary from time to time due to several

factors if that is the case when can we

say that there is a constant

acceleration let's have a review about

uniformly accelerated motion or uam look

at the picture shown in your screen

are you familiar with these blue

uniformed men who are usually positioned

in the busy streets

you might have seen them as you cross

the streets to reach your school or on

your way to the market or a friend's

house they are the traffic enforcers who

are they and what do they do they play a

crucial role in maintaining the flow of

traffic and in implementing loss

and rules and regulations on the road

that every motorist should follow

they may also be considered as front

liners amidst the coveted 19 pandemic as

they assess soldiers and police officers

in checkpoints speed limits are observed

on roads they vary and depend on several

conditions speed limits for highways are

different from speed limits on small

avenues and streets this prevents

vehicles to speed up or accelerate

unnecessarily in our bc streets as they

are being monitored by traffic enforcers

acceleration is defined as the rate of

change in velocity with time it is a

vector quantity having both magnitude

and direction

acceleration of vehicles usually changes

from time to time a vehicle may speed up

as it travels to highways or slow down

as it approaches an intersection

it should also help when the stop light

is red and eventually accelerate when

the light turns green we can say that

most type of acceleration that we

observe is not constant or non-uniform

due to these factors

when you are riding a vehicle you can

say that speeds up or slows down based

on its speedometer a speedometer

indicates the speed of a vehicle it is

usually combined with a device known as

odometer but records the distance

traveled assume that you are riding a

vehicle and observed these speedometer

readings

what can you say about the readings on

the speedometer during each minute

what can you infer from the data in the

table

this means that vehicle speeds up

every minute there is one kilometer per

hour increase on the speed of the

vehicle the increase for every minute is

constant therefore we can say that the

vehicle has uniform acceleration this

vehicle exhibits a uniform or constant

acceleration it is a type of motion in

which the velocity of an object changes

by an equal amount in every equal time

period just like these examples in

uniformly accelerated motion or uam the

value of the acceleration is constant it

does not change the velocity changes but

at a constant rate an object with zero

acceleration is said to be in uniform

motion an object in uniformly

accelerated motion has non-zero but

constant acceleration

acceleration represents how velocity

changes with time velocity represents

how position changes with time

next picture

as you can see

we have a coin toss it upward

does it stay up

no

when it reaches its maximum height

eventually it will go down what makes it

go down

the answer is

gravity

gravity pulls the coin down things that

are thrown upward will go down because

of these force gravity also pulls us

towards the earth that is why we are not

being thrown outside the space what

floor was your classroom when you were

in grade 7 in grade 8

was it on the 3rd or 4th floor

which is easier climbing to your

classroom or going down to the school

canteen

when you climb a high place you go

against gravity when you are on a high

place and you go down you are moving

toward gravity so you use less force

same is true with free falling objects

objects at free fall also exhibit

uniformly accelerated motion

the acceleration due to gravity is 9.8

meter per second squared neglecting air

resistance it is a constant acceleration

for all falling bodies regardless their

mass and weight all objects on the

earth's surface are being accelerated

towards the center of the earth at a

rate of

9.8 meter per second squared this means

that if you raise an object above the

surface of the earth and drop it

the object will start from res and its

velocity will increase 9.8 meter per

second

for each second it is falling toward the

earth's surface until it strikes the

ground

in general a uniformly accelerated

motion is the one in which the

acceleration of a body throughout the

motion is uniform it can be observed in

either vertical or horizontal dimension

and into dimensions

let us have an activity for you to

understand the uniformly accelerated

motion

analyze each scenario identify if it

exhibits uniformly accelerated motion or

not let us have the first photo a bike

at rest

is this uam or not

the answer

not uam

next

a fruit dropping from a tree

is this an example of uam or not

the answer uam

next

a boy holding a book

and we answer

not uam

next

rocks falling from a cliff

is this a uniformly accelerated motion

or not

the answer

uam

last picture

a trok running with a constant

acceleration

is it uam or not the answer

it is an example of uam

great job class you did well now let us

proceed let us take a look of these

photo as you can see there is a photo of

a man diving

the motion of the man as it dives into

the water is moving along a curved path

due to a natural force called

gravitational force or gravity

gravity is the natural force that causes

object to fall towards the earth hence

the acceleration due to gravity is

always directed downwards with this the

motion of the man undergoes projectile

motion projectile motion is a form of

motion where an object moves in a curved

path the object that is thrown or

projected and exhibits projectile motion

is called projectile the curve-like path

undertake by a projectile is called

trajectory let us have another photo are

you familiar with this game

a sepak takraw player kicking a rotten

ball over the net what is the projectile

in that scenario

if you think that the rattan ball is the

projectile then you are right how do you

describe its trajectory

the rotten ball traveling on a curved

path that is correct in mathematical

terms we call this pattern parabola an

angle launch projectile exhibits a full

parabolic trajectory motion

this shows that as the player kick the

rattan ball in the air the ball will

eventually go back to the ground still

due to gravity as it moves horizontally

hence projectile motion consists of

horizontal and vertical motion working

independently the two pictures and

scenarios that i have shown you are the

two types of projectile motion

horizontally launched projectiles

and angle-launched projectiles let us

take note of their components in

horizontal motion it is the x component

no resistance in any form to simplify we

neglect air resistance next

there is a constant horizontal velocity

we use vx to represent it v for velocity

and x for horizontal component

next horizontal acceleration is zero

why because there is no external force

acting along the horizontal motion it

means that acceleration does not exist

and it is represented as a x a for

acceleration and x for the x component

next we call the horizontal distance as

range and it is represented as dx d for

distance and x for the horizontal

component

now let us go to the vertical motion

this is the y component the force acting

upon in this motion is the force of

gravity and it is represented as

g

or a y

or acceleration in the y or in the

vertical motion or acceleration due to

gravity the constant acceleration is

always equal to negative 9.8 meter per

second squared take note class that

negative indicates the direction and the

direction is downward

due to the presence of gravity

accelerating at 9.8 meter per second

squared this causes the vertical

velocity to increase

which makes it not constant and it is

represented as v y v for velocity and y

for the vertical component or vertical

motion

next we call the vertical distance as

the height

and it is represented as h

or d y for you to understand more let us

have an example scenario this is an

example of a horizontal launched

projectile

suppose you roll a marble on a

frictionless table observe the motion of

the marble as it goes down the floor

the motion of the marble is gradually

increasing from point a to point b due

to the presence of gravity accelerating

at 9.8 meter per second squared these

cause the vertical velocity to increase

which makes it not constant for the

horizontal velocity there is no external

force acting along the horizontal motion

which means no acceleration resulting to

a constant horizontal velocity

let us have an example problem to solve

a marble is thrown horizontally from a

table top with a velocity of 1.50 meter

per second

the marble falls 0.70 meters away the

table's edge

find the following how high is the table

and what is the final velocity of the

marble just before it hits the cup first

let us illustrate the problem a marble

is thrown horizontally with an initial

velocity of 1.50 meter per second we are

going to represent it as vi or initial

velocity

next the marble falls at 0.70 meter away

from the table

therefore we can say that it is the

horizontal distance or dx and that is

again 0.70

meters next we are going to find how

high the table is

or our vertical distance or d y and also

if we have initial velocity of course we

have the final velocity

of the marble before it touches the cup

and it is represented as vf or the final

velocity now let us solve the problem

here are the given and the formulas that

we are going to use again our given the

horizontal distance is 0.70 meters our

initial velocity which is equal to 1.50

meter per second and our acceleration

due to gravity is 9.8 meter per second

squared

to find the height or the vertical

distance of the table this is our

formula get the one half of the product

of acceleration due to gravity and the

squared of time as you can see we do not

have the value of time therefore we need

to get first the time to get the height

of the table so take note of this

formula let us substitute our given to

our formula time is equal to dx which is

0.70 meters divided by the initial

velocity 1.50 meter per second

let us divide

0.70 divided by 1.50

and the answer

is 0.47

this is already rounded off

next how about the unit as you can see

we can cancel out meters so let's cancel

out meters and the remaining unit is

second therefore our final answer is

0.47

second

now we can determine the height of the

table let's substitute the given

in our formula

acceleration due to gravity times time

which is 0.47 do not forget to get the

square of the time divided by 2 squaring

0.47 we get

0.2209 seconds squared

next let us simplify this by multiplying

the acceleration due to gravity and time

therefore we have

2.16482

divided by 2.

as you can see we can cancel out second

square and the remaining unit is meters

next let us divide this

into two and the quotient is

[Music]

1.08 meters this is also rounded off

therefore this is our final answer the

height of the table is 1.08

meters now let's proceed to our next

question

what is the final velocity of the marble

just before it hits the cup

as you can see we have an additional

given that we got a while ago which is

the height or the vertical distance

1.08 meters

to find the final velocity this is the

formula that we are going to use

negative of the square root of 2 times a

g times d y let us substitute the given

to our formula so here it is we have the

tu

the ag or the acceleration judo gravity

and our height

multiplying these three quantities we

are going to have

21.168

also we do the operation in the units

next to simplify this we have to get the

square root of 21.168

and the square root of our unit m

squared per second squared therefore we

have

4.6

meter per second

let's not forget that we have here a

negative sign take note class that the

negative sign indicates downward

direction

therefore we can say that the final

velocity of the marble just before it

hits the cup is 4.6 meter per second

downward or

negative 4.6

meter per second and that is our final

answer

and that is how you are going to solve

that problem

and that's it for our lesson for today

check out the part two of this lesson

before we end let us have a shout out

shout out to

audrey z vlog

shout out to

gab kalugdan

shout out to kritom

also shout out to

marisol marphiel

and shout out to bayawan city science

and technology education center negros

oriental thank you all so much for

watching i really appreciate it if you

like share subscribe and comment down

below for a shout out see you guys on my

next video bye

[Music]