Centre of Mass

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Centre of Mass - Examples

Although the mass of an object is spread out across its body, it is possible to find a single point where all of the mass appears to be. This point is called the object’s centre of mass.

All in a single point

The centre of mass is the point through which an object’s weight appears to act.

Hanging objects

If an object is hung from a string, it will hang with its centre of mass directly below the point that it is hung from.

Toppling over

An object will fall over if its centre of mass is outside its base.
An object will fall off a surface if its centre of mass isn’t over the surface.

Forces & Motion

1.1

Basics of Motion

1.1.1Average Speed 1.1.2Acceleration 1.1.3Distance & Displacement 1.1.4Velocity 1.1.5Adding Vectors 1.1.6Distance-Time Graphs 1.1.7Speed-Time Graphs 1 1.1.8Speed-Time Graphs 2 1.1.9Initial & Final Speed, Acceleration, Distance 1.1.10Average Speed - Calculations 1.1.11Acceleration - Calculations 1.1.12Uniform Acceleration - Calculations 1.1.13Grade 9 - Motion 1.1.14Exam-Style Questions - Graphs of Motion

1.2

Forces

1.2.1Contact & Non-Contact Forces 1.2.2Examples of Contact Forces 1.2.3Friction 1.2.4Newton's First Law 1.2.5Newton's Second Law 1.2.6Newton's Third Law 1.2.7Describing Forces 1.2.8Using Free Body Diagrams

1.3

Effects of Forces

1.3.1Momentum - No Impulse 1.3.2Momentum 1.3.3Momentum: Law of Conservation 1.3.4Force & Momentum Change 1.3.5Momentum - Safety 1.3.6Change in Momentum - Calculations 1.3.7Momentum - Calculations 1.3.8Mass 1.3.9Weight 1.3.10Centre of Mass 1.3.11Gravity - Calculations 1.3.12Free Fall 1.3.13Air Resistance & Friction 1.3.14Graphs of Motion with Air Resistance 1.3.15Turning Effect 1.3.16Moments 1.3.17Equilibrium 1.3.18Moments - Calculations 1.3.19Exam-Style Questions - Moments

1.4

Stopping Distance

1.4.1Stopping Distance 1.4.2Stopping Distance - Thinking Distance 1.4.3Stopping Distance - Braking Distance

1.5

Forces & Elasticity

1.5.1Stretching, Bending & Compressing 1.5.2Elastic Deformation vs Inelastic Deformation 1.5.3Hooke's Law 1.5.4Hooke's Law - Equation 1.5.5Hooke's Law - Spring Experiments 1.5.6Hooke's Law - Calculations 1.5.7Elastic Potential - Calculations 1.5.8End of Topic Test - Forces 1.5.9Exam-Style Questions - Elastic Potential

Electricity

2.1

Electricity in Homes

2.1.1Mains Electricity 2.1.2Power Rating of Appliances 2.1.3National Grid 2.1.4AC/DC 2.1.5Electrical Safety 2.1.6Fuses 2.1.7Fuse Ratings

2.2

Current & Potential Difference

2.2.1Current 2.2.2Current - Equation 2.2.3Current - Calculations 2.2.4Conductors & Insulators 2.2.5Electrical Conductors - Electrons 2.2.6Potential Difference 2.2.7Potential Difference - Equation 2.2.8Measurements in Circuits 2.2.9Voltage - Calculations

2.3

Resistance & Power

2.3.1Resistance 2.3.2Ohm's Law 2.3.3Measuring Resistance 2.3.4Resistance & Ohms Law - Calculations 2.3.5Variable Resistance 2.3.6Current-Voltage Graph for a Resistor 2.3.7Electrical Work 2.3.8Power 2.3.9Heating Effect in Resistors 2.3.10Electrical Work - Calculations 2.3.11Exam-Style Questions - Resistance

2.4

Electric Circuits

2.4.1Circuit Diagrams 2.4.2Circuit Symbols 2.4.3Diodes 2.4.4LDRs & Thermistors 2.4.5Series Circuits 2.4.6Resistors in Series 2.4.7Series Circuits - Calculations 2.4.8Parallel Circuits 2.4.9Parallel Circuits in Practice 2.4.10End of Topic Test - Electricity 2.4.11Grade 9 - Circuits 2.4.12Exam-Style Questions - Electrical Circuits

2.5

Static Electricity

2.5.1Electric Charge 2.5.2Charging an Object 2.5.3Charged Objects 2.5.4Uses of Static Electricity 2.5.5Charge Dangers 2.5.6Calculating Power & Energy Transferred

Waves

3.1

Wave Basics

3.1.1Wave Basics 3.1.2Transverse Waves 3.1.3Longitudinal Waves 3.1.4Wave Frequency Formula 3.1.5Wavelength & Amplitude 3.1.6Wave Speed 3.1.7Wave Speed - Calculations 3.1.8Wave Frequency - Calculations 3.1.9Wavefronts 3.1.10Doppler Effect 3.1.11Exam-Style Questions - Wave Speed

3.2

Waves at a Boundary

3.2.1Changing Wave Motion 3.2.2Reflection 3.2.3Refraction 3.2.4Angle of Refraction 3.2.5Refractive Index 1 3.2.6Refractive Index 2 3.2.7Total Internal Reflection 3.2.8Optic Fibres

3.3

Electromagnetic Spectrum

3.3.1Properties of Electromagnetic Waves 3.3.2Gamma Rays 3.3.3X-Rays 3.3.4UV Light 3.3.5Visible Light 3.3.6Infrared Radiation 3.3.7Microwaves 3.3.8Radio Waves 3.3.9End of Topic Test - EM Waves 3.3.10Exam-Style Questions - Electromagnetic Wave Uses

3.4

Sound Waves

3.4.1Sound Waves 3.4.2Sound Waves & Our Ears 3.4.3Sound as a Wave 3.4.4Signal Generators 3.4.5Sound Waves - Oscilloscope Traces 3.4.6Measuring the Speed of Sound - Experiment 3.4.7End of Topic Test - Waves

3.5

Communications

3.5.1Digital & Analogue Signals 3.5.2Benefits of Digital Signals

Energy Resources & Energy Transfers

4.1

Energy Changes

4.1.1Energy Stores 4.1.2Conservation of Energy 4.1.3Examples of Energy Conversion 4.1.4Kinetic Energy Stored 4.1.5Gravitational Potential Energy Stored 4.1.6Elastic Potential Energy Stored 4.1.7Changes in Kinetic Energy - Calculations 4.1.8Changes in GPE - Calculations 4.1.9Changes in EPE - Calculations 4.1.10Mechanical Work Done 4.1.11Mechanical Work Done - Equation 4.1.12Power 4.1.13Mechanical Work - Calculations 4.1.14Electrical Work Done- Calculations

4.2

Energy Losses & Efficiency

4.2.1Energy Wastage 4.2.2Energy Transfer Diagrams 4.2.3Efficiency 4.2.4Reducing Unwanted Energy Transfer 4.2.5Efficiency - Calculations 4.2.6Grade 9 - Energy & Efficiency 4.2.7Exam-Style Questions - Energy & Power

4.3

Energy Resources

4.3.1Energy Resources 4.3.2Fossil Fuels 4.3.3Geothermal Energy 4.3.4Wind Energy 4.3.5Water Energy 4.3.6Tidal Energy 4.3.7Nuclear Energy 4.3.8Solar Energy 4.3.9Non-Renewable & Renewable Resources 4.3.10Renewable Energy 4.3.11Limits to Renewable Energy Resources 4.3.12End of Topic Test - Energy

4.4

Thermal Processes

4.4.1Radiation 4.4.2Conduction 4.4.3Molecular Conduction 4.4.4Convection Currents 4.4.5Convection Currents - Examples

Solids, Liquids & Gases

5.1

Density & Pressure

5.1.1Density 5.1.2Density Equation 5.1.3Calculating Density 5.1.4Density - Calculations 5.1.5Pressure 5.1.6Atmospheric Pressure 5.1.7Pressure Difference 5.1.8Pressure - Calculations

5.2

Changing State

5.2.1Changes of State 5.2.2States of Matter 5.2.3Specific Heat Capacity 5.2.4Exam-Style Questions - Specific Heat 5.2.5Internal Energy - Calculations

5.3

Ideal Gases

5.3.1Kelvin Scale & Absolute Zero 5.3.2Temperature & the Kelvin Scale 5.3.3Properties of Gases 5.3.4Temperature Increase in a Gas 5.3.5End of Topic Test - Solids, Liquids & Gases 5.3.6Grade 9 - Solids, Liquids & Gases

Magnetism & Electromagnetism

6.1

Magnetism

6.1.1Magnetism 6.1.2Magnetic Materials 6.1.3Hard & Soft Magnets 6.1.4Induced Magnetism 6.1.5Magnetic Forces 6.1.6Magnetic Field Patterns 6.1.7Exam-Style Questions - Magnetic Fields

6.2

Electromagnetism

6.2.1The Magnetic Effect of a Current 6.2.2Magnetic Field around a Coil of Wire 6.2.3Magnetic Field Strength 6.2.4The Motor Effect 6.2.5Direction of the Motor Effect 6.2.6The Catapult Experiment 6.2.7Force on a Current Carrying Wire 6.2.8DC Motors 6.2.9Loudspeakers

6.3

Electromagnetic Induction

6.3.1Electromagnetic Induction 6.3.2Induced Potential Difference 6.3.3Alternating Current - The Rotating-Coil Generator

6.4

Transformers

6.4.1Transformers 6.4.2Transformer Equation 6.4.3Step-Up & Step-Down Transformers 6.4.4Principles of Transformer Operation 6.4.5High-Voltage Transmission & Transformers 6.4.6Transformers - Calculations 6.4.7Transformers 2 - Calculations 6.4.8Energy in Transformers 6.4.9Power Losses in Cables 6.4.10End of Topic Test - Magnetism 6.4.11Grade 9 - Transformers 6.4.12Exam-Style Questions - Transformers

Radioactivity & Particles

7.1

Atoms

7.1.1Atomic Model 7.1.2Structure of an Atom 7.1.3The Charges of Sub-Atomic Particles 7.1.4Alpha Particles 7.1.5The Model of the Atom 7.1.6Proton & Nucleon Numbers 7.1.7Atoms & Ions 7.1.8Isotopes 1 7.1.9Isotopes 2 7.1.10Carbon Nuclides

7.2

Radioactivity

Astrophysics

8.1

Motion in the Universe

8.1.1The Solar System 8.1.2Gravitational Field Strength 8.1.3Orbits 8.1.4Orbital Motion

8.2

Evolution of Stars

8.2.1Life Cycle of a Star like the Sun 8.2.2Life Cycle of a Star Much Bigger than the Sun 8.2.3Absolute Magnitude 8.2.4Hertzsprung-Russell Diagrams 8.2.5Exam-Style Questions - Life Cycle of a Star

8.3

Cosmology

8.3.1The Big Bang 8.3.2Evidence for the Big Bang 8.3.3CMB Radiation 8.3.4End of Topic Test - Astrophysics

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