Physics Y9

Energy transfers (spec points 4.2 - 4.10) Energy resources and electricity generation (spec points 4.18p and 4.19p) Density and pressure (spec points 5.3 - 5.7) Movement and position (spec points 1.3-1.10) Forces, movement, shape (spec points 1.11 - 1.24)

Define energy

The ability to do work

Unit of energy

Joule (J)

State the law of conservation of energy

Energy cannot be created or destroyed, only transferred

What is useful energy?

Energy transferred in a desired way

What is wasted energy?

Energy transferred in unwanted ways (often as heat)

What is efficiency?

How much useful energy output is produced from input

Efficiency formula

Efficiency = useful output ÷ total input

Efficiency percentage

Efficiency (%) = (useful output ÷ total input) × 100

Name energy stores

Kinetic, thermal, chemical, gravitational potential, elastic potential, nuclear, magnetic, electrostatic

Define kinetic energy

Energy of moving objects

Kinetic energy formula

KE = ½mv²

Define gravitational potential energy

Energy due to height

GPE formula

GPE = mgh

Define elastic potential energy

Energy stored when stretched/compressed

What is work done?

Energy transferred when a force moves an object

Work done formula

W = F × d

Define power

Rate of energy transfer

Power formula

P = E ÷ t

Unit of power

Watt (W)

What is electrical energy formula

E = VIt

Define conduction

Transfer of heat through solids

Define convection

Heat transfer by movement of fluids

Define radiation

Transfer of heat by infrared waves

What type of surfaces absorb heat best

Dark, dull surfaces

What surfaces reflect heat best

Light, shiny surfaces

Renewable energy resources

Solar, wind, hydro, tidal, geothermal, biomass

Non-renewable resources

Fossil fuels, nuclear

Advantages of renewable energy

Will not run out, low pollution

Disadvantages of renewable energy

Unreliable, expensive, dependent on weather

Advantages of fossil fuels

Reliable, high energy output

Disadvantages of fossil fuels

CO₂ emissions, global warming

What is global warming?

Increasing Earth temperature due to greenhouse gases

What is density

Mass per unit volume

Density formula

Density = mass ÷ volume

Unit of density

kg/m³ or g/cm³

Rearranged density formulas

mass = density × volume

volume = mass ÷ density

Define pressure

Force per unit area

Pressure formula

Pressure = force ÷ area

Unit of pressure

Pascal (Pa)

What increases pressure

Increase force or decrease area

Define liquid pressure

Pressure exerted by a liquid

Liquid pressure formula

Pressure = density × g × height

What affects liquid pressure

Density, gravity, depth

What is upthrust

Upward force exerted by fluid

When does floating occur

Upthrust = weight

Define speed

Distance travelled per time

Speed formula

speed = distance ÷ time

Unit of speed

m/s

Define velocity

Speed in a given direction

Define acceleration

Rate of change of velocity

Acceleration formula

a = (v - u) ÷ t

Define deceleration

Negative acceleration

What is distance-time graph used for

Shows speed

Gradient of distance-time graph

Speed

What is velocity-time graph used for

Shows acceleration

Gradient of velocity-time graph

Acceleration

Area under velocity-time graph

Distance travelled

Define resultant force

Overall force acting on object

What happens if resultant force = 0

Object moves at constant velocity

Define Newton’s First Law

An object remains at rest or constant velocity unless acted on by force

Define Newton’s Second Law

F = ma

Define Newton’s Third Law

For every action, equal and opposite reaction