physipics

FOUR:

PARTICLES

NOTE: The Talk-About Frames below are samples of a much larger, and growing, collection. Scroll down to see the current list.

evidence for very tiny particles 

Frame P1

P1: Some evidence that matter is made of very tiny particles

Syllabus / specification points:

• Ideas about particles explain chemical changes, crystals, and more

• Diffusion – a process of natural mixing of liquids and gases – is only possible if the substances are made of separate particles that can move and have empty spaces between them

• Since particles of matter are invisible we must use models to think about them; the simplest model is a ball

states of matter

P2: States of matter

Syllabus / specification points:

• Particle ideas explain the existence of three states of matter – solid, liquid and gas

• Solids can be explained as structures of particles which are held in fixed locations by inter-particle forces

• Liquids can be explained as having similar inter-particle distance but weaker inter-particle forces, so that particles are not in fixed locations

• Gases can be explained as having particles with very weak inter-particle forces and so freedom for particles to move apart; the particles can have high speed

• A material, such as water, can exist in any of the three states, with changes to particle energy, and inter-particle forces, without change to the particles themselves

Frame P2

density and particles

Frame P3

P3: Density and particles

Syllabus / specification points:

• Particles have mass

• Density of a sample of material can be increased is the particles move closer together; this doesn’t change the mass of the sample, but reduces its volume

• Substances with particles with more mass tend to have higher density than those with lower mass (provided inter-particle distance is the same)

• The space between particles is empty

• Gases have low density because of the large inter-particle spacing

• Density = mass / volume

• The unit of density is the kg/m3

density predictions

Frame P4

P4: Density predictions

Syllabus / specification points:

• The equation for predicting density is: density = mass / volume; we can use this to predict the mass of a known volume of a material, or the volume of a known mass


pressure

P5: Pressure

Syllabus / specification points:

• We experience different pressures in different locations – under the sea, in the atmosphere at sea level, in the atmosphere at high altitude, in space

• pressure = force /area

• The unit of pressure is the pascal, which is the same size as one newton per square metre

• Atmospheric pressure at sea level varies, but is about 100 000 Pa

• Space is a vacuum, and there is no pressure


Frame P5

pressure and particles

P6: Pressure and particles

Syllabus / specification points:

• The atmosphere exerts pressure because of collisions by many fast-moving molecules of air – it’s a molecular bombardment 

• Where there are no molecules (in space) there is no atmospheric pressure

• Where there are fewer molecules per cubic metre (lower density) there is lower atmospheric pressure



underwater pressure

P7: Underwater pressure

Syllabus / specification points:

• Pressure is defined by the equation: pressure = force/area, and is measured in pascals, Pa.

• Pressure due to liquid is dependent on liquid density ( rho ), the gravitational field strength (g) and the depth (h).

• Total pressure on a diver is the pressure due to water plus atmospheric pressure at the surface.

• Pressure due to a liquid (or a gas) creates an upwards force, called upthrust.



bubble pressure I

upthrust, floating and sinking

P8: Bubble pressure I

Syllabus / specification points:

• Molecules of gas move at high speed and collide with the surfaces. These collisions produce pressure on the surfaces.

• There is nothing in the spaces between molecules.

• Gases can be compressed; the molecules become closer together so there are then more molecules, and more mass, per cubic metre

• If temperature stays the same (or doesn’t change too much) then there are more frequent collisions between molecules and surfaces (such as the inside of a tank or cylinder). So there is more pressure on the surfaces.

• In a stable (fixed size and shape) bubble under water the outward pressure due to the gas is equal to the inward pressure due to the surrounding water.



bubble pressure II

P9: Upthrust, floating and sinking

Syllabus / specification points:

• Molecules of gas move at high speed and collide with the surfaces. These collisions produce pressure on the surfaces.

• There is nothing in the spaces between molecules.

• Gases can be compressed; the molecules become closer together so there are then more molecules, and more mass, per cubic metre

• If temperature stays the same (or doesn’t change too much) then there are more frequent collisions between molecules and surfaces (such as the inside of a tank or cylinder). So there is more pressure on the surfaces.

• In a stable (fixed size and shape) bubble under water the outward pressure due to the gas is equal to the inward pressure due to the surrounding water.



P10: Bubble pressure II

Syllabus / specification points:

• Pressure is bigger at bigger depths in liquids, including water.

• When the volume of a mass of gas is smaller the molecules are closer together.

• Collisions with the walls of a container (such as the inner surfaces of a bubble) happen more often, provided that the temperature of the gas doesn’t change too much.

• More frequent collisions, at the same speed, means more pressure.

• When volume decreases (for a fixed mass of gas at constant temperature) the pressure increases.

• Likewise, when volume increases collisions are less frequent and pressure decreases.

• The relationship between pressure and volume for a fixed mass of gas at constant temperature is an inverse one.



Particles, provisional list, May 2021


Comp: completed and ready, but so far unpublished


P1        Some evidence that matter is made of particles                             FREE

P1.B    All in bits                                                                                           planned 

P2        States of matter                                                                               FREE

P2.B    Condensation and Evaporation                                                       planned

P3        Density and particles                                                                      FREE 

P3.B    Expansion and contraction                                                             planned

P4        Density predictions I                                                                       FREE

P4.B    Density predictions II                                                                      planned 

P5        Pressure                                                                                         FREE

P6        Pressure and particles                                                                   FREE

P7        Underwater pressure                                                                     FREE

P8        Bubble pressure I                                                                           FREE

P9        Upthrust, floating and sinking                                                        FREE

P9.B    A Titanic story                                                                                planned

P10      Bubble pressure II                                                                          FREE

P11      Pressure & volume of a fixed mass of gas at constant temp’re.               Comp

P11.B   Bouncy castle Physics                                                                  planned

P12      Pressure and temperature of a fixed mass of gas at constant volume.    Comp 

P12.B   Pain relief                                                                                       planned 

P13      kelvin: a unit of temperature that starts at the beginning              Comp

P13.B   Temperatures here and there                                                        planned

P14      Changes of pressure, volume, and temperature I                         Comp

P15      Changes of pressure, volume, and temperature II                        Comp

P16      Electric charge and particles                                                         Comp

P17      More about models                                                                       Comp

P18      A discovery that atoms must have internal structure                    Comp

P19      Alpha particles act as ionising radiation                                        Comp

P20      The discovery of electrons                                                            Comp

P20.B   Small particles, big impact                                                            planned

P20.C   Electronic mega store                                                                   planned

P21      The plum pudding hypothesis                                                       Comp

P22      Alpha scattering                                                                            Comp

P23      Atoms have nuclei                                                                         Comp

P23.B   Plasma ball                                                                                    planned 

P24      Protons and neutrons                                                                    Comp 

P25      Carbon nuclei                                                                                Comp

P25.B   Numbers, numbers                                                                       planned

P26      Carbon isotopes                                                                            Comp

P27      Beta emission                                                                                Comp

P28      PET scans                                                                                     planned

P29      Alpha emission                                                                              planned  

P29.B   Uranium isotopes                                                                          planned

P30      Fire safety                                                                                      planned

P31      Gamma emission                                                                           planned

P32      Cures for cancer                                                                            planned    

P33      Particles from the Sun: aurorae                                                     planned

P34      Cosmic radiation                                                                            planned

P35      Half-life                                                                                           planned 

P35.B. Half-life and nuclear waste                                                            planned

P36      Choosing isotopes                                                                        planned

P37      Background radiation                                                                    planned

P38      Splitting - fission                                                                            planned

P39      The Sadako Story                                                                          planned

P40      Starting off small - fusion                                                              planned

P41      Ending up big – fusion                                                                   planned 







All ’comp’ (completed) Frames are available at low cost.

Copyright (c) David Brodie, 2019-2021

Photography: Adobe Stock