Physics Mock 2023

Density

Mass / Volume

Density of Solids, Liquids & Gas

-Solids and Liquids have similar densities (space between particles does not change significantly but usually liquids have a lower density)

-Gases have a far lower density (spacing between atoms increases greatly because particles have lots of energy to move so volume increases greatly)

What happens to mass during change of state?

It’s conserved

Changes of state are..

Physical and reversible

not chemical - material retains it’s original properties when reversed

What is internal energy?

Energy stored by particles (atoms and molecules) within a system

Takes form of kinetic energy (vibration of atoms etc) or potential energy (between particles)

What happens to particles when heated?

Energy particles have is increased

This increases internal energy (either raises temp of system or produces a change of state)

What is specific heat capacity?

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

change in thermal energy = mass × specific heat capacity × temperature change

Specific Latent heat

The amount of energy needed to change the state of 1kg of a substance without a change in temperature

The substance needs to be at the right temperature to change state first

Specific Latent Heat of fusion is energy to melt/freeze

Specific Latent Heat of vaporisation is energy to boil/condense

Energy for a change of state

energy for a change of state = mass × specific latent heat

Energy when melting, freezing and condensing

Energy is absorbed when melting and evaporating and energy is released when freezing and condensing.

Sublimation

Solid → Gas

Molecules of gas

In constant random motion

What is temperature of gas related to?

average kinetic energy of the molecules

Higher temp in a gas…

the greater the average kinetic energy and so the faster the average speed of the molecules

gas pressure

Molecules colliding with container = exert a force on wall

The total force exerted by all of the molecules inside the container on a unit area of the walls is pressure

Changing the temperature of a gas held at a constant volume

changes the pressure exerted by the gas (known as the Pressure law)

Changing volume of gas

Affects pressure

Increasing the volume in which a gas is contained (at constant temperature) = decrease in pressure (Boyle’s law)

due to the reduced number of collisions per unit area.

A gas can be compressed or expanded by pressure changes. This pressure produces..

net force at right angles to the wall of the gas container (or any surface).

increasing the volume of a container

decrease in pressure

Doing work on a gas…

increases it’s temperature

Work done

Pressure x Volume

What does doing work on a gas mean?

compressing or expanding the gas, so changing the volume

Adding more particles to a fixed volume

-Pressure increases

-Energy transferred w/ pressure, so temp increases

Fixed number of particles, smaller volume

-Particles collide with wall (moving inward)

-Particles gain momentum (rebound velocity faster than inward velocity)

-As particle has greater velocity, pressure increases

-Temp increases (kinetic energy increases)

System

An object or group of objects

When a system changes, the way energy is stored changes

Example of system - ball rolling and hitting wall

-System is moving ball

-When it hits wall, some of the kinetic energy is transferred as sound

Elastic potential

The type of energy stored in a spring when it is stretched

Specific Heat Capacity

The energy required to raise the temperature of 1kg of a substance by 1°C or 1K.

Power

rate at which energy is transferred or the rate at which work is done

Power = Energy Transferred / Time

Energy Transfers

-Energy CANNOT be created or destroyed

-It can be transferred and stored usefully or dissipated

What happens to energy in a system change?

Energy is dissipated - stored in less useful ways

Often described as being ‘wasted’

How to reduce energy waste?

Lubrication (oil in motor → reduces friction so less energy lost as heat)

Thermal insulation (double glazing → less useful thermal energy lost)

higher thermal conductivity of a material means

heat is allowed to travel through the material more easily, so the higher the rate of energy transfer by conduction across the material

Thermal conductivity in a building

-Rate of cooling low IF walls are thick and thermal conductivity of walls are low

-if walls are thin metal sheets, conductivity would be lost quickly

Efficiency

ratio of useful work done by machine, engine etc to energy supplied to it - often expressed as a percentage

efficiency = useful energy output / total energy output

energy can be replaced with power ^

How can efficiency of a system be increased?

-Reducing waste output (e.g lubrication, thermal insulation)

-Recycling waste output (e.g absorbing thermal waste and recycling as input energy)

Main Non-Renewable energy resources

-Fossil Fuels (coal, oil, gas)

-Nuclear Fuel

Main Renewable energy resources

- Biofuel

-Wind

-Hydro-electricity

-Geothermal

-Tidal

-Solar

-Water waves

Renewable energy

energy which can be replenished as it’s used

What is non-renewable energy used for?

used more for large-scale energy supplies due to the large energy output per kilogram of fuel

Why has renewable energy become more important?

due to the finite lifetime of fossil fuels

Why is renewable energy not the most reliable?

Solar doesn’t work in bad weather or night

Wind is only intermittent.

What are the main energy uses?

Transport

Electricity generation

Heating

Environmental impact - extraction of energy

Fossil fuels involve destroying landscapes

Wind turbines can be considered an eyesore

Evironmental impact - use of energy sources

Fossil fuels release harmful emissions

Solar, wind directly create electricity with no emissions

When + why did fossil fuels become an important source of energy?

Industrial revolution

Easy to mine, provided a lot of energy

Why is renewable energy only recently more useful?

Technology has had to develop alot to be able to harness sources efficiently

Why is it harder to solve environmental issues surrounding energy use?

political, social, ethical and economic considerations

Speed (velocity)

Distance / Time

Acceleration

Rate of change of velocity

Change in Velocity / Time taken

Force

a push or pull that acts on an object due to the interaction with another object

all forces are either non-contact or contact

Uniform Acceleration Equation

v² - u² = 2as

Final Velocity - Initial Velocity = 2 x acceleration x distance

Scalar

Magnitude (size) but no direction

Generally cannot be negative

Vector

Magnitude (size) and direction.

Can be represented by arrows (length / size = magnitude)

Displacement

a vector quantity that means the distance travelled in a straight line from the start to the finish AND the direction of that straight line

Typical speed of a person walking

1.5 metres per second

Typical speed of a person running

3 metres per second

Typical speed of a person cycling

6 metres per second

Typical speed of sound waves in the air

330 metres per second

Typical speed of a car

25 metres per second

Typical speed of a train

55 metres per second

Typical speed of a plane

250 metres per second

Velocity

Vector quantity that is speed in a given direction

When an object moves in a circle

it may travel at constant speed BUT the velocity will

be constantly changing because velocity is a vector quantity that depends on speed and direction

Distance-Time Graph: Curved upwards line means

the object is accelerating and a tangent must be drawn to find speed

DTG vs VTG gradient.

DTG - Speed
VTG - Acceleration

distance

how far an object moves

scalar quantity

displacement

includes both distance, measured in a straight line, and direction of that line

vector quantity

velocity

speed in a given direction

factors that will effect the speed a person moves

age, terrain, fitness, distance travelled

Why do we calculate average speed?

it’s rarely constant

Stopping distance of a vehicle

Stopping distance = thinking distance (driver’s reaction time) + braking distance

Greater speed for a given braking force means..

greater stopping distance

Typical reaction times

vary from 0.2 to 0.9s

factors that can affect a driver’s reaction time

tiredness, distractions, drugs and alcohol

Longer reaction times..

increase thinking distance

factors affecting braking distance

adverse road

weather conditions (icy, wet)

poor condition of vehicle (breaks, tires)

When force is applied to vehicle breaks

work done by friction force between breaks and wheel reduces kinetic energy of vehicle and temperature of breaks increases (thermal energy store increases)

Greater speed of vehicle means..

greater breaking force required to stop vehicle in a certain distance

Greater breaking force

greater deceleration of vehicle

What are the dangers of large decelerations?

breaks could overheat

driver could lose control of vehicle

Typical stopping distance at:

20mph

30mph

40mph

50mph

60mph

70mph

avg car length = 4 metres

3 cars

6 cars

9 cars

13 cars

18 cars

24 cars

Forces involved in deceleration

-when breaking hard, large deceleration

-force felt on passangers and cars

large deceleration = large change in momentum over a short time, so a large force exerted on the object (person!)

Description of our Solar System

-The Sun

-8 Planets

-Natural Satellites (moons)

-Dwarf Planets: Pluto, Ceres

-Asteroids, comets