Particles
Why a balloon deflates
A balloon’s air seems to escape because its skin has millions of holes so tiny
that molecules of inner air can escape through them. This is how the balloon
deflates.
What is diffusion
Diffusion means one substance spreading through another.
For example, when we open a perfume, its molecules spread around the room
and collide with moving air particles.
Why gases expand more than solids
Gas molecules are already expanded which makes attraction among them
weaker. On the other hand, molecules in solids are close to each other thus less
expandable.
How air pressure keeps a balloon inflated
When air molecules are blown into a balloon through breath, they move around
rapidly. When they hit the walls they push and millions of small pushes become
air pressure.
When the balloon is inflated where is the air pressure highest?
Inside it, because it is a small space with millions of tiny air molecules moving
rapidly.
Solid
Liquid
Gas
Element, Compound and Mixture
What is an element. Why is carbon called Element
An Element is a chemical substance that cannot be broken into anything similar.
That is because it is made up of only one type.
Carbon is an Element because it is made up of carbon atoms only
Describe an ATOM
An atom is the smallest part of an element that can exist and take part is a
chemical reaction. Atoms are far too small to see with an ordinary microscope.
Their size can differ depending on the chemical element. (e.g., Gold atoms are
bigger than hydrogen atoms)
Name 3 parts of an atom
Except the Hydrogen atom, all atoms are made of 3 smaller particles,
Protons – They have a positive charge (+ve)
Neutrons – These have No charge. They are neutral
Electrons – These have negative charge (-ve)
Why is Carbon Dioxide a good gas for fire extinction?
Carbon Dioxide is denser than air and settles down over the fire putting it off
Why is Liquid Nitrogen used to freeze food?
It does not burn or let things burn in it. Does not react with other elements
easily.
It is cold and freezes food fast.
Why is Argon used in light?
It is used for filling light bulbs. The argon filament surrounding the bulb can get
very hot without burning. It also does not allow other things to burn in it.
Difference between Physical and Chemical change
Physical Change,
No new substances ae made and the change is usually reversible
Chemical Change,
A new substance is made and the change is normally difficult to reverse
Metals vs Non-Metals,
Metals Non-Metals
Dense and feel Heavy Not very Dense and feel Light
Shiny appearance when polished Dull appearance
High boiling point Raw boiling point
Difficult to melt usually gases or solids which melt easily
Malleable (can be bent) Brittle or powdery
Forces and their effects
What is force, what is its measuring Unit and how do we call its
measuring meter
A force is a push or pull upon an object that causes changes on its state.
The measuring unit is Newton (N)
The measuring meter is Newton meter
What is density. What means that water has a density of 1g/cm3.
Density is equal to Mass/Volume.
The unit used is g/cm3 or Km/m3.
For example, Lead has higher density than wood because it has more mass in
every cm.
Water Density is 1g/cm3;
If an object has lower density than water, it will float. If it has higher density it
will sink.
The denser the liquid the greater the upthurst: Ships float higher in sea water
than in fresh water, because sea water is denser.
What is Air Resistance
It is a force formed by Air molecules bumping each other.
Why objects float or sink in water?
Because of the object density. If an object has lower density than water, it will
float. If it has higher density it will sink. Water Density is 1g/cm3;
W= m x g
means Weight = Mass x Gravity
Q. A robot of 100 kg mass is built on earth where gravity is 9.8/kg.
If the robot goes to Mars, where gravity is 3.7/kg what is the robot’s weight
on both places:
Weight on Earth:
W=mxg
W = 100 x 9.8
W = 980 N
Weight on Mars:
W=mxg
W = 100 x 3.7
W = 370 N
The solar system
What is a day
The Earth spins on an axis through the North and South Poles.
One complete rotation of the Earth takes 1 day or 24 h to complete (23.93 h
actually)
What is a year
The Earth revolves around the Sun. One Orbit takes around 365.25 days or 1
year to complete. Since 365.25 is not a round figure, an extra day is produced
every 4 years on February 29th in order to adjust the calendar year with the solar
year, and this will be called a Leap year.
What is an eclipse
When a planet or the moon block off light from another, an eclipse takes place
There are 2 types of eclipse, SOLAR and LUNAR
