Chapter 6: Matter, Models and Explanations

What is density?

Density is the mass per unit volume: ρ = m ÷ V

What are the units of density?

kg/m³

Why do gases have much lower density than solids or liquids?

Because particles are further apart and have more energy, increasing volume

Does mass change when a substance changes state?

No, mass remains constant

What is specific heat capacity?

The amount of energy required to raise the temperature of 1 kg of a substance by 1°C

What is the equation for specific heat capacity?

ΔE = mcΔT

What is the unit of specific heat capacity?

J/kg°C

What is specific latent heat?

Energy required to change the state of 1 kg of a substance without changing its temperature

What is the specific latent heat of fusion?

Energy required to melt or freeze a substance

What is the specific latent heat of vaporisation?

Energy required to boil or condense a substance

What is the equation for specific latent heat?

E = mL

What is internal energy?

Energy stored by particles in a system as kinetic and potential energy

What happens to internal energy when a substance is heated?

It increases

What is sublimation?

When a solid changes directly into a gas

During heating

what happens at the melting point?,Temperature stays constant while energy is used to change state

During heating

what happens at the boiling point?,Temperature stays constant while energy is used to change state

Are changes of state physical or chemical?

Physical

Is mass conserved in a change of state?

Yes

What is pressure in terms of particles?

Force per unit area exerted by particles colliding with container walls

What is the particle model of solids?

Particles vibrate around fixed positions

What is the particle model of liquids?

Particles vibrate and move past each other

What is the particle model of gases?

Particles move freely in random directions

How does heating affect particle motion?

Particles move faster, increasing temperature and kinetic energy

What is the Pressure Law?

For a fixed volume of gas, increasing temperature increases pressure

What is deformation?

A change in shape

What is elastic deformation?

Object returns to its original shape after the load is removed

What is plastic deformation?

Object does not return to its original shape after the load is removed

What does Hooke's Law state?

Extension of an elastic object is proportional to the force applied, F = kx

What is the spring constant?

k, measured in N/m

What is the equation for work done on a spring?

W = ½ kx²

What is pressure in a gas?

Force per unit area due to particle collisions

How does increasing volume affect gas pressure?

Pressure decreases (Boyle's Law)

What is the equation for gas pressure and volume?

P × V = constant

Why does atmospheric pressure decrease with height?

There is less air above a unit area at higher altitude

What is upthrust?

Upward force on a submerged object due to pressure difference

When does an object float?

When its weight is less than the weight of the displaced fluid

What is the equation for fluid pressure?

p = hρg

What factors affect fluid pressure?

Depth (h), density (ρ), gravitational field strength (g)

What is the solar system?

Sun at centre, 8 planets, dwarf planets, moons, asteroids, comets

Which planets are rocky?

Mercury, Venus, Earth, Mars

Which planets are gas giants?

Jupiter, Saturn, Uranus, Neptune

Why do larger planets have rings?

Strong gravity attracts debris

What causes planets to orbit the Sun?

Gravitational force causes constant change of direction

How does orbital speed change if a planet moves closer to the Sun?

Orbital speed increases

How does a star form?

Gas/dust cloud collapses under gravity, temperature and pressure rise, fusion starts

What is the main fusion process in stars?

Hydrogen nuclei fuse to form helium

What is equilibrium in a star?

Energy from fusion balances gravitational collapse

What happens when a star runs out of gas?

It collapses as it is no longer in equilibrium

How is work done on a gas related to temperature?

Doing work increases the energy of particles, increasing temperature

How does adding more particles to a fixed volume affect pressure?

Pressure increases due to more collisions

How does compressing gas increase pressure and temperature?

Particles collide more frequently and with greater momentum

What is red shift?

Light from galaxies moving away appears shifted to red wavelengths

What does red shift indicate?

Universe is expanding

What is CMBR?

Cosmic Microwave Background Radiation, leftover radiation from the early universe

How does CMBR support the Big Bang?

Shows the universe was hot and dense, and has expanded and cooled

Why is the Big Bang model widely accepted?

It explains red shift and CMBR, matching observations