Decelerations

Work Done when Braking

When we push the brake pedal, brake pads are pressed onto the wheels. This contact causes friction. This causes work to be done. The work done between the brakes and the wheels converts (changes) energy from kinetic energy in the wheels to thermal energy in the brakes. The temperature of the brakes then increases.

Higher speed

The greater the speed of a vehicle, the greater the braking force needed to stop the vehicle before a certain distance.
- This means that more work needs to be done on the brakes to stop the car.

Higher mass

The greater the mass of the vehicle, the greater the braking force needed to stop the vehicle. This means that more work needs to be done on the brakes to stop the car.

Higher grip

For the same work done, the stopping distance will decrease if the force (grip) between the road and the vehicle increases.

Estimating forces

When a car comes to a stop, the work done by the brakes must equal the initial kinetic energy of the car.
Work done = initial kinetic energy.
F d = ¹⁄₂ m v².
We can use this equation to estimate the force applied by the brakes.

Dangers of Large Decelerations

The greater the braking force, the greater the deceleration of the vehicle. Large decelerations can cause brakes to overheat and/or the car to skid. A larger deceleration will transfer more stopping force to passengers. This harms passengers. Compare these situations:

Traffic lights

When a typical family car decelerates at a set of traffic lights, only a small force is exerted on (applied to) the passengers.
This is because the deceleration happens over a long period of time.
The force should not be enough to harm the passengers.

Emergency stop

When a typical family car suddenly stops on the road to avoid a collision, a greater force is exerted on (applied to) the passengers.
This is because the deceleration happens over a shorter period of time.

Crash

When a typical family car suddenly is stopped by a crash, an even greater force is applied to the passengers than the last example.
This is because the deceleration happens in even less time.
This could harm passengers.

1Energy

1.1Energy Changes

1.1.1Energy Stores

1.1.2Energy Storing

1.1.3Internal Energy

1.1.4Kinetic Energy Storage

1.1.5Gravitational Potential Energy Storage

1.1.6Elastic Potential Energy Storage

1.1.7Calculating Changes in Energy

1.1.8Changes in Kinetic Energy - Calculations

1.1.9Changes in GPE - Calculations

1.1.10Changes in EPE - Calculations

1.1.11Energy Transfers

1.1.12Energy Transfer Examples

1.1.13Mechanical Work Done

1.1.14Mechanical Work Done Equation

1.1.15Mechanical Work - Calculations

1.1.16Electrical Work Done

1.1.17Power

1.1.18Electrical Work Done- Calculations

1.2Energy Losses & Efficiency

1.2.1Energy Wastage

1.2.2Efficiency

1.2.3Reducing Energy Loss

1.2.4Power & Energy Transfer

1.2.5Efficiency - Calculations

1.2.6Grade 9 - Energy & Efficiency

1.3Energy Resources

1.3.1Energy Resources

1.3.2Fossil Fuels

1.3.3Geothermal Energy

1.3.4Wind Energy

1.3.5Water Energy

1.3.6Tidal Energy

1.3.7Nuclear Energy

1.3.8Solar Energy

1.3.9Original Source of Energy

1.3.10Non-Renewable and Renewable Resources

1.3.11Uses of Energy Sources

1.3.12Changing Electricity Use

1.3.13Renewable Energy

1.3.14End of Topic Test - Energy

1.3.15Exam-Style Questions - Energy

2Electricity

2.1Electric Charge

2.1.1Circuit Diagrams

2.1.2Circuit Symbols

2.1.3Current

2.1.4Current Equation

2.1.5Current - Calculations

2.1.6Conductors

2.1.7Potential Difference

2.1.8Voltage Equation

2.1.9Measurements in Circuit

2.1.10Voltage - Calculations

2.2Resistance & Electrical Work

2.2.1Resistance

2.2.2Resistance Graph

2.2.3Diodes

2.2.4LDRs and Thermistors

2.2.5Electrical Work

2.2.6Power

2.2.7Ohm's Law

2.2.8Resistance and Ohms Law - Calculations

2.2.9Electrical Work - Calculations

2.3Electric Circuits

2.3.1Series Circuits

2.3.2Resistors

2.3.3Cells

2.3.4Potential Difference

2.3.5Series Circuits - Calculations

2.3.6Parallel Circuits

2.3.7Parallel Current

2.3.8Parallel Resistance

2.3.9Lights in Parallel

2.3.10Parallel Circuits - Calculations

2.3.11Grade 9 - Circuits

2.3.12Exam-Style Questions - Electricity

2.4Electricity in Homes

2.4.1AC/DC

2.4.2Mains Electricity

2.4.3Power Ratings

2.4.4National Grid

2.4.5Domestic Uses - Calculations

2.4.6Fuses & Circuit Breakers

2.4.7Earthing

2.4.8Dangers of the Live Wire

2.4.9End of Topic Test - Electricity

2.5Static Electricity

2.5.1Electrical Charge

2.5.2Charging an Object

2.5.3Charged Objects

2.5.4Static Electricity

2.5.5Electric Fields

3Particle Model of Matter

3.1States of Matter

3.1.1Atomic Model

3.1.2Atomic Structure

3.1.3Sub-Atomic Particles

3.1.4Models of the Atom

3.1.5Alpha Particles

3.1.6Electron Arrangements

3.1.7Density

3.1.8Density Equation

3.1.9Density and the Particle Model

3.1.10Density - Calculations

3.1.11Changes of State

3.1.12Exam-Style Questions - Density

3.2Heat

3.2.1Internal Energy

3.2.2Change in Thermal Energy

3.2.3Specific Heat Capacity Experiment

3.2.4Equation for Heat Capacity

3.2.5Leslie's Cube

3.2.6Internal Energy - Calculations

3.2.7Melting and Boiling

3.2.8Latent Heat

3.2.9Energy Change for Change of State

3.2.10Latent Heat - Calculations

3.2.11Latent Heat Experiments

3.3Particle Motion in Gases

3.3.1States of Matter

3.3.2Properties of Gases

3.3.3Temperature Increase in a Gas

3.3.4Work Done on a Gas

3.3.5End of Topic Test - Particle Model of Matter

3.3.6Grade 9 - Particle Model of Matter

3.3.7Exam-Style Questions - Specific Heat Capacity

4Atoms & Radiation

4.1Atoms

4.1.1Atomic Model

4.1.2Structure of an Atom

4.1.3Sub-Atomic Particles

4.1.4Alpha Particles

4.1.5The Model of the Atom

4.1.6Electron Arrangements

4.1.7Proton and Nucleon

4.1.8Atoms and Ions

4.1.9Isotopes

4.1.10Carbon Nuclides

4.1.11Exam-Style Questions - Atomic Structure

4.2Radiation

5Forces

5.1Basics of Motion

5.1.1Velocity

5.1.2Average Speed

5.1.3Adding Vectors

5.1.4Acceleration

5.1.5Distance vs Displacement

5.1.6Contact and Non-Contact Forces

5.1.7Distance-Time Graphs

5.1.8Speed-Time Graphs

5.1.9Average Speed - Calculations

5.1.10Acceleration - Calculations

5.1.11Uniform Acceleration - Calculations

5.1.12Grade 9 - Motion

5.1.13Exam-Style Questions - Motion

5.2Forces

5.2.1Mass and Inertia

5.2.2Weight

5.2.3Centre of Mass

5.2.4Gravity - Calculations

5.2.5Resultant Forces

5.2.6Newton's First Law

5.2.7Newton's Third Law

5.2.8Newton Second Law - Calculations

5.2.9Free Body Force Diagrams

5.2.10Components of Forces

5.2.11Free Body Diagrams - Calculations

5.2.12Stretching a Spring

5.2.13Hooke's Law and Equation

5.2.14Spring Experiment

5.2.15Hooke's Law - Calculations

5.2.16Elastic Potential Energy

5.2.17Elastic Potential - Calculations

5.2.18Exam-Style Questions - Elastic Potential Energy

5.3Effects of Forces

5.3.1Acceleration

5.3.2Air Resistance and Friction

5.3.3Graphing Acceleration

5.3.4Momentum

5.3.5Momentum: Law of Conservation

5.3.6Force and Momentum Change

5.3.7Change in Momentum - Calculations

5.3.8Momentum - Calculations

5.3.9Moments

5.3.10Equilibrium

5.3.11Moments - Calculations

5.3.12Circular Motion

5.3.13Levers & Gears

5.3.14Stopping Distance

5.3.15Factors Affecting Stopping Distance

5.3.16Decelerations

5.3.17Stopping Distance - Calculations

5.4Pressure

5.4.1Pressure & Force on Container

5.4.2Atmospheric Pressure

5.4.3Liquid Pressure

5.4.4Pressure - Calculations

5.4.5Liquid Pressure - Calculations

5.4.6Upthrust

5.4.7Pressure Difference

5.4.8End of Topic Test - Forces

5.4.9Exam-Style Questions - Pressure

6Waves

6.1Wave Basics

6.1.1Wave Basics

6.1.2Wave Speed Formula

6.1.3Wave Speed Equation

6.1.4Wave Speed - Calculations

6.1.5Wave Frequency Formula

6.1.6Wavelength and Amplitude

6.1.7Wave Frequency - Calculations

6.1.8Transverse Waves

6.1.9Longitudinal Wave

6.1.10Required Practical - Ripple Tank

6.2Waves at a Boundary

6.2.1Waves at a Boundary

6.2.2Reflection of Light

6.2.3Refraction of Light

6.2.4Internal Reflection

6.3Sound Waves

6.3.1Sound Waves

6.3.2Sound Waves and our Ears

6.3.3Speed of Sound

6.3.4Speed of Sound Experiment

6.3.5Sound as a Wave

6.3.6Uses of Sound Waves: Ultrasound Waves

6.3.7Uses of Sound Waves: Earthquakes

6.3.8Sound Waves - Calculations

6.3.9End of Topic Test - Introduction to Waves

6.3.10Exam-Style Questions - Wave Speed

6.4Electromagnetic Waves

6.4.1Properties

6.4.2Gamma Rays

6.4.3X-Rays

6.4.4UV Light

6.4.5Infrared Radiation

6.4.6Microwaves

6.4.7Radio Waves

6.4.8Properties 2

6.4.9Visible Light

6.4.10Specular and Diffuse Reflection

6.4.11Colours

6.4.12Grade 9 - Waves

6.5Lenses

6.5.1Lenses

6.5.2Convex Lens

6.5.3Concave Lens

6.5.4Lenses - Calculations

6.5.5Images

6.5.6Ray Diagrams

6.6Heat & Radiation

6.6.1Infrared Radiation

6.6.2Radiation & Surface Colour

6.6.3Surface Area & Temperature

6.6.4Temperature

6.6.5Greenhouse Effect

6.6.6Energy Balance of the Earth

6.6.7End of Topic Test - EM Waves, Lenses & Heat

6.6.8Exam-Style Questions - EM Radiation

7Magnetism

7.1Magnetism Basics

7.1.1Magnetism

7.1.2Magnetic Materials

7.1.3Induced Magnetism

7.1.4Magnetic Fields

7.1.5Magnetic Field Patterns

7.2Electromagnetism

7.2.1The Magnetic Effect of a Current

7.2.2Solenoid Field

7.2.3Magnetic Field Strength

7.2.4Uses of Electromagnets

7.2.5Motor Effect

7.2.6Magnetic Flux Equation

7.2.7Magnetic Flux - Calculations

7.2.8Electric Motors

7.2.9Force Acting on a Coil in a Magnetic Field

7.2.10Induced Potential Difference

7.2.11Magnetic Field Direction

7.2.12Forces Between Electricity and Magnets

7.2.13AC/DC

7.2.14Generator Effect

7.3Transformers

7.3.1Transformers

7.3.2Transformer Equation

7.3.3Step-Up and Step-Down Transformers

7.3.4Principles of Transformer Operation

7.3.5High-Voltage Transmission and Transformers

7.3.6Energy in Transformers

7.3.7Power Losses in Cables

7.3.8Transformers - Calculations

7.3.9Transformers 2 - Calculations

7.3.10End of Topic Test - Magnetism

7.3.11Grade 9 - Transformers

7.3.12Exam-Style Questions - Magnetic Fields

8Astrophysics

8.1Astrophysics

8.1.1The Solar System

8.1.2The Sun

8.1.3The Solar System - Calculations

8.1.4Orbits

8.1.5Stable Orbits

8.1.6Orbits HyperLearning

8.1.7Life Cycle of a Star

8.1.8Creation of Elements

8.1.9Red-shift

8.1.10The Big Bang Theory

8.1.11Gaps in Knowledge

8.1.12End of Topic Test - Astrophysics

8.1.13Exam-Style Questions - Astrophysics

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