8th grade

Force, Motion, and

Energy – Science
Chapter 3
Ms Laili - SMPI AL ABIDIN SURAKARTA
 Table of contents

01 02 03 04
Force and Speed Describing Turning
Energy
Movement Force

05 06 07
Pressure Pressure in Particles on
between solid liquids and gasses the move
3.1
Forces and
Energy
 Forces
Forces is pull, push, or twist that act on
an object.
 What do you think
about not moving
object?
There are forces
acting on the object
or not?

Yes, there are forces act on an object.

 Requirement Balanced and
Unbalanced Force

Balanced Unbalanced
100 N 100 N 1. Equal size but not opposite
direction
2. Not equal size but opposite
direction
3. Not equal size and not opposite
Equal size of forces direction
Opposite direction of force
Effect of Unbalanced Force on an Object

Change position Change movement

Because the object Change speed (speeding
start to move up or slowing down)

Change Direction Change Shape

Object go back in the Object can change their
opposite direction shape because of forces
3.2
SPEED
What is Speed?
Speed is distanced travelled per unit
time.
 Unit Of Speed

meters per Kilometers per Miles per hour

second (m/s) hours (km/h) (ml/h)
Standard units of speed Common units of speed Units of speed in
in most of contries another contries
 Calculating Speed

Average speed is sometimes used because the speed of an

object during a journey is not always constant.
 Work Example
Kesya rode her bike around the park for 120 meters in
60 seconds. Calculate the average speed of the Kesya
riding!
Answer:
𝑫𝒊𝒔𝒕𝒂𝒏𝒄𝒆𝒅 𝟏𝟐𝟎 𝒎
𝑺𝒑𝒆𝒆𝒅 = = =𝟐 𝒎 𝒔
𝑻𝒊𝒎𝒆 𝟔𝟎 𝒔
 Work Example

Rama is in a car travelling at a speed of 35 m/s. How

long will the car take to travel 2100 m?
Answer:
𝑫𝒊𝒔𝒕𝒂𝒏𝒄𝒆𝒅 𝟐𝟏𝟎𝟎 𝒎
𝑻𝒊𝒎𝒆 = = = 𝟔𝟎 𝒔
𝑺𝒑𝒆𝒆𝒅 𝟑𝟓 𝐦/𝒔
It's time to
Practice! 
 Steps to Practice

Working on
Make a groups of 2
theoretical Checked by Ms Laili
members
questions in class

stick the questions

Look for paper
Present the on the paper that
calculation
calculation results has been
questions about
in front of the class distributed, then
speed
work on the paper.
3.3
Describing
Movement
 How to describing movement?

EXPLANATION

GRAPH
Descrining Movement with a Graph
 D’
A’
Let’s
Practice
!
3.4
Turning
Force
Effect of force that rotate
around an axis or change
direction
 Turning effect of force Lever
happen when there are pivot
and lever.

Pivot : The point around which

the lever turns

Lever : The object that turns

Direction of turning effect =

Dirction of force
How to calculate the
turning effect of force?
MOMENT EQUATION

MOMENT M=Fxd
Turning effect of force
M = moment (Nm)
The moment of force depends on : F = Force (N)
1. The size of force D = distance (m)
2. The distance between position
where the force act and the pivot
 Comparation moment equation
Balancing
Moment 1 = Moment 2
Force 1 x dsitance 1 = Force 2 x distance 2
How to make 2 moment
balance?

Use comparation between 2

moment
 Let’s Practice!

SCIENCE BOOK
QUESTION PAGE 95
 3.5
Pressure
between Solid
 What is Pressure?

PRESSURE

THE PUSHING EFFECT OF FORCE

When your foot is stepped on by the marked part of
the shoe, which one hurts the most?

A B C
Why, give your reason!
How to Calculate Pressure Equation of Pressure

Amount of pressure depend

on :
1. Amount of force
2. Amount of area

1. Bigger force, bigger pressure P = Pressure (N/𝒎𝟐 atau N/𝒄𝒎𝟐 atau N/𝒎𝒎𝟐 )
2. Bigger area, smaller F = Force (N)
A = Area (𝒎𝟐 , 𝒄𝒎𝟐 , 𝒅𝒎𝟐 )
pressure
 Work Example
10 m
● There is a box weighing 15 m 5m
10,000 N on the floor. If
the base area of the box ● Calculate the pressure of
is 20 𝒎𝟐 . The pressure the box, if the force of
experienced by the floor the box is 1500 N.
is...
Answer
A = s x s = 15 m x 5 m = 75 𝒎𝟐
Answer
𝑭 𝟏𝟎.𝟎𝟎𝟎 𝑵
𝑷=𝑨= = 500 N/𝒎𝟐 𝑷=
𝑭
=
𝟏𝟓𝟎𝟎 𝑵
= 20 N/𝒎𝟐
𝟐𝟎𝒎𝟐 𝑨 𝟕𝟓 𝒎𝟐
 Let’s Practice

Make a grup consist

of 3 person

Do the excercise

Get the best score

(for the group that answer fastest and most
correctly)
 Do exercise 
1. A woman is applying 300 N/𝒎𝟐 of pressure onto a door with her hand. Her
hand has area 0.02 𝒎𝟐 . Work out the force being applied!.
2. A force of 180 N is applied to a square of side length 3 m. Calculate the pressure
of the square!
3. A man with a weight of 750 N is standing on one leg. His foot is
exerting 24 N/𝒎𝟐 of pressure onto the ground. What is the surface area of the
bottom of his foot?
4. An object has a diameter 14 m, and force of the object is 924 N. Calculate the
pressure of the object!
14 m
 ANSWER
1. F = P x A = 300 N/𝒎𝟐 x 0.02 𝒎𝟐 = 6 N
𝑭 𝟏𝟖𝟎
2. P = = = 𝟐𝟎 𝑵/𝒎𝟐
𝑨 𝟑𝒙𝟑
𝑭 𝟕𝟓𝟎
3. A = = = 𝟑𝟏. 𝟐𝟓 𝒎𝟐
𝑷 𝟐𝟒
𝟐𝟐
4. A = 𝐱 𝟕 𝐱 𝟕 = 𝟏𝟓𝟒
𝟕
𝑭 𝟗𝟐𝟒
P= = = 𝟔 𝑵/𝒎𝟐
𝑨 𝟏𝟓𝟒
 3.6
Pressure in
Liquids and Gases
 Pressure in Liquid

Why the wall in Why does it feel heavier whe we

the DAM is walk on water than on land?
wider at the
bottom?
 Did you know?
● Why the wall in the DAM is wider at the bottom?

Because to make the wall stronger where the pressure

from the water

● Why does it feel heavier whe we walk on water than on

land?

Because pressure in a liquid increase with depth

As you go deeper
in a liquid, there
is more liquid
above you
 Pressure in Gases

Gases pressure inside the ballon Gases pressure inside the ballon

= >
Gasses pressure outside the ballon Gasses pressure outside the ballon
 Pressure in Gases

Gases pressure inside the ballon Gases pressure inside the ballon

= <
Gasses pressure outside the ballon Gasses pressure outside the ballon
Temperature and Pressure
ALTITUDE AND GAS PRESSURE

Altitude is height above sea level.

Higher altitude = lower pressure
 WHERE DO LIQUIDS AND GASES
PRODUCE PRESSURE?
● Particles in a liquid and gas move randomly and collide with the
walls of the container.
● The more particles there are in in a gas or liquid, the more
collision happen with the object, and so the force and the
pressure increase.

● Pressure in Gas depends on :

 Amount of Particle
 Temperature
 Depth
 3.7
Particles On the
move
 Did You Know ???

How can you smell food When you pour orange juice into
cooking when you are some water, why does all the liuid
distance away from the food? eventually turn orange?
Movement Liquid and Gas Particle

Speed of Particle and Direction of

the Particle is Random

The movement of particle is called

diffusion
 Diffusion Particle

● Diffusion is random movement of particles from higher

concentration area to lower concentration area.
● Concentration is the number of particles in a particular
volume.
Speed of Diffusion depends on :

The different
concentration
of the particle Temperature

The bigger the

difference in
concentration of the The higher the
particle temperature
= =
the faster the diffusion the faster the diffusion
THANK YOU
SEE YOU IN THE NEXT MEETING
 Plot roller coaster
Resolution Fill in the blanks

Conflict

Rising action

Setting

Falling action
 Force and motion questions
The length of a line between two points A change in an object’s position

A. Distance B. Matter A. Air resistance B. Balanced forces

C. Force D. Speed C. Motion D. Gravity

The path that a moving object follows A push or a pull

A. Friction B. Direction A. Force B. Mass

C. Position D. Distance-time C. Distance-time D. Distance

 Types of energy
Fill in the blanks

Light Thermal Sound Electrical Chemical

Music TV Heater Petrol Voice

Gas Sunlight Batteries Bell Bulb

Fire Firelight Coal Computer Microwave

 True or false
Force = mass/acceleration Mass is the volume an object has

True False True False

When accelerating, the forces are balanced Velocity is time and speed

True False True False

Acceleration = change of velocity x time A force can be a push or a pull

True False True False