Year 8 Physics

forces are measured in newtons using a spring balance
there are two main force categories:
- contact
- friction, buoyancy, tension, applied forces
- non-contact
- normal forces, gravitation, magnetism, electrostatic forces
force definitions:
- frictional force - the force exerted by a surface as an object moves across it or makes an effort to do so
- air resistance - a special type of frictional force that acts upon objects as they travel through the air
- tension force - force that is transmitted through a string, rope, cable or wire when it is pulled tight by forces acting on opposite ends
- spring force - the force exerted by a compressed or stretched string upon any object attached to it

gravity is increased by mass or distance
weight - a force and changes depending on gravity - mass multiplied by gravitational force
mass - amount of matter, stable
types of friction - static (between 2 non moving items), sliding (object moving over another, rolling (e.g. ball)
newtons first law - remains in motion unless acted upon by an unbalanced force

many different types of energy - heat, sound, mechanical, nuclear, chemical etc.
energy can be hard to define, but it is:
- the ability to do work
- work occurs when changes occur to matter
- work = force x distance
- W = F x s
energy is measured in the same unit as work: joules

2 main types of energy : kinetic and potential
- kinetic - moving
- potential - a store of energy ; can happen but hasn’t happened yet
heat / thermal - the interhal motino of the atoms is called heat energy
- can be produced by friction
- causes changes in any form of matter
chemical energy - energy that is available for release from chemical reactions
- chemical is energy to required to bond atoms together, but when the bonds are broken, energy is released
- example: fuel or food
electromagnetic energy - waves of energy
- light, x-rays, lasers, commonly used in power lines
nuclear energy
- radioactive atoms have an unstable nucleus which causes it to split
- when the nucleus splits it releases energy
sound energy
- anything that makes a noise has this form of energy
mechanical energy - anything that moves

energy transfer - energy is transferred from one object to another
- examples:
- frying an egg
- kicking a soccer ball
- opening a door
- dropping something
- throwing something
energy transformation - energy is transformed from one energy type to another
- burning something !!
- lighting a light bulb
- driving a car

temperature - the amount of heat energy available for work in a system
- this relates to the average kinetic energy
higher temperatures means higher moving particles
heat flows from hot to cold
- thermal equilibrium - the same temperature
all phases of matter expand with higher temperature
heat transfer is a transfer of kinetic energy - heat is energy in transit, and measured in joules
- heat will always flow from hot to cold until thermal equilibrium
- heat is transferred via three processes - conduction, convection and radiation
conduction - particles that are very close together can transfer heat energy as they vibrate. this type of heat transfer is called conduction
solids are good at conducting heat while liquids and gases are worse