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