YEAR7 ENGSCI FINAL
atoms
number of proton+nuetron in the nucleus is called the nucleon number or mass
atom has no electric charge, it is electricity neutral( positive protons and negative electrons in the atom is equal)
Light
a way of transferring energy,
source that gives out light are luminous
travel
light can travel through empty space, it doesn't require a medium, substance to travel through
light travels in a straight line
object that does'nt gives out light are non-luminous, but transmit, reflect or absorb light
light can be transmitted by objects it hits, or be reflected, or can be absorbed
Energy cannot disappear, energy of light is transferred into thermal energy, absorbing light makes the object heats a bit
see through clear glass------transparent
frosted glass, half transparent------translucent
materials that light cannot travel throu such as bricks------opaque
Law of reflection
when light is reflected on a smooth and shiny surface, the imput ray is INCIDENT RAY, the oupu ray is Reflection, symbols: (i) , (r)
according to the law of reflection: The INCIDENT RAY is = to the reflection ray
Normal line – line between the angle of incidence and angle of reflection forming a right angle with the
surface
Reflection – bouncing of light as it strikes a surface
Reflection and Images
the image we see in the mirror is the image of reflection, it always apear to be the same distance with the object that it is reflecting
VIRTUAL image
A virtual image is an upright image that is achieved where the rays seem to diverge. VIRTUAL IMAGES ARE laterally INVERTED(镜像）
Real image
A real image is formed when rays converge
Reflections from a rough surface are diffused and do not form an image
Refraction
when light travels through different mediums, it might change the light's direction, the bend of the ligt is called REFRACTION
if the light travels from a less dense medium to a more dense medium ( air->water) the light ray stick towards to the normal
happens between boundary and interface
more dense-> less dense then the light ray move away from the medium
refractive index: the speed of light and reflection
Refractive index=speed of light in a vaccum/ speed of light in the medium
eye little reminder
Light from an object is focused by the lens and cornea on the retina of the eye. The retina sends signal to the brain.
Earth in space
Rotation
seasons
At any time, sun lights up half of the earth, the other half is in shadow
Earth spins on its axis, day and night are caused by the Earth spinning every 24 hours( aniticlockwise)
Revolution
the movement of the earth around the sun along its orbit once a year or 365 days.(公转）
The earth’s axis is tilted by 23.5 degrees, causing the Earth to have diferent seasons, however places near to the euqator has less changes
Night sky
can be seen in a night sky: stars, planets, dwarf planets, asteroids, moon, comets, meteors, meteorites, and man-made satellites.
Atoms are made up of protons (positively charged), electrons (negatively charged), and neutrons (no charge).
protons and neutrons make up the nucleus, nucleus is at the centre of an atom
Electrons orbit the nucleus
Neutral atoms have equal number of protons and electrons.
atoms hold together
nucleus positively charged, electrons negatively charged individual atom is held together by the electrostatic attraction
Discover of electrons
•Thomson discovered electrons using a cathode ray tubes and made a model out of that discovery.
• Plum pudding model – an analogy for Thomson’s model of the atom
what the model discovered
- Atoms have a central nucleus.
- Most of the mass of the atom is the nucleus.
- The nucleus has a net positive charge.
- A nucleus is surrounded by empty space in which electrons move.
The number of protons in the nucleus of an atom is its proton number
The number of neutrons = nucleon number - proton number
• Proton number – total number of protons in an atom of an element
• Nucleon number – total number of neutrons in an atom.
Isotopes – atoms of the same element with different numbers of neutrons.
pure substance&Chromatography
one substance only,can be an element or a compound
drinking sea water
desalination removes salt, dissolved substances from the sea water, safe to drink
boil sea water->steam->travels through condenser->cool down, condense->pure liquid drips in to the beaker, salt remains in the flask
Purity – how much of a substance is in a mixture
Chromatography
Chromatography – a method used to separate and identify substances dissolved in a solvent
Chromatography of ink – different dyes in the ink move at different speeds in a chromatography paper so
they separate
solutions and concentration
concentration
The concentration(浓度） of a solution is a measure of the number of solute particles in a volume of solution.
Solution（溶液）a mixture that forms when a solute dissolves in a solvent. Examples: salt and water, sugar and water
Dilute solution（稀释溶液） – there are few solute particles in a certain volume of solution
Concentrated solution（浓缩溶液）there are many solute particles in a volume
Solubility
Saturated solution(饱和溶液) – contains the maximum mass of solute that will dissolve.
Solubility(溶解度) – is the maximum mass of a substance that dissolves in 100 g of water.
The higher the temperature the higher is the solubility of a substance.
Chemical reactions
Corrosion reactions
• A reaction that happens on the surface of a metal.
• Corrosion of iron is called rusting.
iron + oxygen + water → hydrated iron oxide (rust)
• Corrosion is a slow reaction.
• Painting the surface, coating oil or grease, galvanizing, and making alloys are some of the ways to prevent corrosion
Lifestyle and Health
diet
food you eat each day, supply you
with everything you need to stay healthy.
Carbohydrate
store a lot of energy which your body uses easily.
Protein
You need protein to build new tissues, replace old tissues and repair damaged tissues. Foods rich in protein include meat, fish and insects, eggs, peas, beans and nuts
Your body breaks down the proteins you eat into amino acids, then builds those amino acids back into the proteins it needs
Lipids - fats and oils - are a very important source of energy for your body. Fats are solid lipids and oils are liquid lipids.
Fat cells store energy in your body. Fat cells also make an insulating layer under your skin and form a protective layer around organs like your kidneys.
Vitamins
Vitamins help chemical reactions
take place in your cells.
Minerals
you only need small amounts of minerals in your diet - but you need them to build different substances in your body. Iron is needed to make haemoglobin to carry oxygen in your blood. Calcium is needed for strong teeth and bones.
Digestion
big insoluble food molecules are broken down into small, soluble molecules which move from your gut into your blood by diffusion. The dissolved nutrients are carried all around your body in the blood to the cells where they are needed.
Carbohydrates, fats and energy
Carbohydrates and lipids - the fats and oils - are the main foods providing animals, including humans, with the energy they need.
sugar
Sugars move quickly by diffusion from your digestive system into your blood, giving you an energy boost
Starch
Starch is a carbohydrate made by plants from lots of sugar molecules. Starch must be broken down by your body, so the energy from starchy foods is released slowly.
glycogen
a carbohydrate, short-term energy store, stored in the liver and muscles
fats
Fat is a long-term way of storing energy in the body. If we do not get enough food, our body breaks down our fat stores to give the cells the energy they need.
Balanced diet
If you eat a balanced diet, you eat a wide variety of foods that give you the nutrients you need in healthy proportions
Different people have different types of diet.
Important:
fiber – for bowel movement, absorption of excess fat in the food.
water – for proper functioning, blood circulation, removal of waste
Ecosystem
An ecosystem is an environment that supports life.
An ecosystem is made up of non-living or abiotic factors, such as the soil, the temperature and the water supply and of living or biotic factors.
factors
• the food supply
• numbers of predators and prey
• diseases and parasites
Habitat – home of an organism
An ecosystem contains a number of different habitats