FORCES
Force is a push or pull (cannot see the force, invisible but can see what they do)
and measured in newtons using a Forcemeter (spring balance)
Force can change the shape of an object and direction (slow it down or speed up)
Types of force: Weight, electrostatic force, magnetic force, friction, air resistance,
water resistance , thrust and tension.
Air resistance - acts on any object through the air
Terminal velocity – steady speed
Streamlining – reduces the air resistance
Gravity – pulls all objects together (toward to the earth)
Mass – the amount of matter
Weight – force of gravity exerted on an object
Friction always tries to slow moving objects down – it opposes motion.
Friction also occurs when things move through air. This is called air resistance.
The amount of FRICTION depends on surfaces of the objects or materials.
The rougher the surface ,the more friction produce.
Friction also produce heat
Friction can be useful force because it prevents our shoes slipping on the
pavement
Sometimes we want to reduce friction : we use oil to reduce the friction
between the moving part inside a car
Gravity is a force that pulls all objects together .
The greater the mass of an object the more gravity it has.
Although every objects(including you!)has a gravitational pull
Weight is a force, measured in newtons .
W=mg or Weight=mass x gravitational strength , (N) , (1kg=10N)
Mass is the amount of matter , measured in kilograms
Mass= FORCE ÷ gravitational strength
The FORCE of gravity is different on different planets on the Moon. Force
measured in Newtons (N)
F= m × g
Mass never changes on other planets however Weight changes
Centripetal force – that keeps something moving in a circle
Energy
Energy - The ability to do work
Joule (or kilojoules) - the unit of energy
Fuel - a material that contains a store of energy and can be burned (gas, oil,
coal, petrol)
Energy is all around you!
You can hear energy as sound.
You can see energy as light.
And you can feel it as wind.
Living organisms need energy for growth and movement.
The six main forms of energy are:
Heat(Thermal)
Electrical
Light
Sound
Chemical
Mechanical
Fuel and food are forms of stored chemical energy.
The Law of Conservation of Energy-Energy can be neither created nor
destroyed by ordinary means.
It can only be converted from one form to another.
Potential Energy- is stored energy.
Stored chemically in fuel, the nucleus of atom, and in foods.
Or stored because of the work done on it:
Stretching a rubber band.
Winding a watch.
Pulling back on a bow’s arrow.
Lifting a brick high in the air.
The formula to find G.P.E. is
G.P.E. = Weight x Height x gravity
G.P.E = m x g x h (1 joule)
Kinetic energy-The energy of motion.
The faster an object moves, the more kinetic energy it has.
The greater the mass of a moving object, the more kinetic energy
it has.
Kinetic energy depends on both mass and velocity.
A Sankey diagram- shows how the energy is divided between useful energy
and wasted energy in a device or a process
useful energy out
Efficiency=
total energy ∈¿× 100 % ¿
SPACE
• Stars emits light , but we can see other objects because they
reflect light from the Sun
• Dwarf planets – orbit the Sun but are smaller than planets
(Pluto)
• Planets are not stars – there are objects in orbit around stars
• Exoplanets are other planets that orbit other Sun
• A Moon is an object that orbits a planet (it is sometimes
called natural satellite)
• A comet is made of ice and dust like a big, dirty snowball
orbiting the Sun
• Meteor a piece of rock or a particle of dust . (when enters the
Earth’s atmosphere and burns up) and when it reach the
ground is called meteorite
• Artificial satellites are man-made objects orbit around the
Earth
• We have day and night because the Earth spins on its AXIS
• It takes 24 hours for the Earth to do one complete spin.
• The Earth spins around once per day.
• When the Earth faces the Sun, it is DAYTIME
• When the Earth faces away from the Sun, it is NIGHTIME
• The change in seasons is caused by the tilt in the Earth’s axis
• The two halves of the Earth are called the North and South
hemisphere
• Because of the tilt, one hemisphere points towards the sun and one
points away. It is summer in the hemisphere that points towards the
sun. It is winter in the hemisphere that points away from the sun.
• Days and night are of equal lengths. 21st March and 21st
September
• Days are longest. 21st June
• Days are shortest. 21st December
