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

2Electricity

3Particle Model of Matter

3.1States of Matter

3.1.1Atomic Structure

3.1.2Atomic Structure 2

3.1.3Density

3.1.4Density - Calculations

3.1.5Changes of State

3.1.6Exam-Style Questions - Density

3.2Heat

3.2.1Internal Energy

3.2.2Heat Capacities

3.2.3Internal Energy - Calculations

3.2.4Latent Heat

3.2.5Latent Heat - Calculations

3.2.6Latent Heat Experiments

3.3Particle Motion in Gases

3.3.1Particle Motion in Gases

3.3.2Particle Motion in Gases 2

3.3.3End of Topic Test - Particle Model of Matter

3.3.4Grade 9 - Particle Model of Matter

3.3.5Exam-Style Questions - Specific Heat Capacity

4Atoms & Radiation

4.1Atoms

4.1.1Atomic Model

4.1.2Atomic Model 2

4.1.3Atoms & Ions

4.1.4Isotopes

4.1.5Exam-Style Questions - Atomic Structure

4.2Radiation

4.2.1Radioactive Decay

4.2.2Radioactive Decay 2

4.2.3Types of Radioactive Emission

4.2.4Fission & Fusion

4.2.5Radioactive Decay Equations

4.2.6Radio. decay equations - Calculations

4.2.7Half Lives & Ionising Radiation

4.2.8Half Life - Calculations

4.2.9Uses & Dangers of Radiation

4.2.10Uses & Dangers of Radiation 2

4.2.11End of Topic Test - Atoms & Radiation

4.2.12Grade 9 - Radiation

4.2.13Exam-Style Questions - Radioactive Decay

5Forces

5.1Basics of Motion

5.1.1Basics of Motion

5.1.2Basics of Motion 2

5.1.3Basics of Motion 3

5.1.4Distance- & Speed-Time Graphs

5.1.5Average Speed - Calculations

5.1.6Acceleration - Calculations

5.1.7Uniform Acceleration - Calculations

5.1.8Grade 9 - Motion

5.1.9Exam-Style Questions - Motion

5.2Forces

5.2.1Gravity

5.2.2Gravity - Calculations

5.2.3Resultant Forces

5.2.4Newton Second Law - Calculations

5.2.5Force Diagrams

5.2.6Free Body Diagrams - Calculations

5.2.7Stretching a Spring

5.2.8Hooke's Law

5.2.9Hooke's Law - Calculations

5.2.10Elastic Potential Energy

5.2.11Elastic Potential - Calculations

5.2.12Exam-Style Questions - Elastic Potential Energy

5.3Effects of Forces

5.3.1Acceleration

5.3.2Acceleration 2

5.3.3Momentum

5.3.4Change in Momentum - Calculations

5.3.5Momentum - Calculations

5.3.6Moments

5.3.7Moments - Calculations

5.3.8Circular Motion

5.3.9Levers & Gears

5.3.10Stopping Distance

5.3.11Decelerations

5.3.12Stopping Distance - Calculations

5.4Pressure

5.4.1Pressure

5.4.2Pressure - Calculations

5.4.3Liquid Pressure - Calculations

5.4.4Pressure Changes

5.4.5End of Topic Test - Forces

5.4.6Exam-Style Questions - Pressure

6Waves

6.1Wave Basics

6.1.1Basics & Formula

6.1.2Wave Speed - Calculations

6.1.3Describing Waves

6.1.4Wave Frequency - Calculations

6.1.5Transverse & Longitudinal Waves

6.1.6Required Practical - Ripple Tank

6.2Waves at a Boundary

6.2.1Waves at a Boundary

6.2.2Waves at a Boundary 2

6.3Sound Waves

6.3.1Sound Waves

6.3.2Sound Waves 2

6.3.3Uses of Sound Waves

6.3.4Sound Waves - Calculations

6.3.5End of Topic Test - Introduction to Waves

6.3.6Exam-Style Questions - Wave Speed

6.4Electromagnetic Waves

6.4.1Properties

6.4.2Gamma, X-Ray & UV Light

6.4.3Infrared, Microwave & Radio Waves

6.4.4Properties 2

6.4.5Visible Light

6.4.6Visible Light 2

6.4.7Grade 9 - Waves

6.5Lenses

6.5.1Lenses

6.5.2Lenses - Calculations

6.5.3Images & Ray Diagrams

6.6Heat & Radiation

6.6.1Infrared Radiation

6.6.2Temperature

6.6.3Greenhouse Effect

6.6.4End of Topic Test - EM Waves, Lenses & Heat

6.6.5Exam-Style Questions - EM Radiation

7Magnetism

7.1Magnetism Basics

7.1.1Magnetic Materials

7.1.2Magnetic Fields

7.2Electromagnetism

7.2.1Electromagnetism

7.2.2Electromagnetism 2

7.2.3Motor Effect

7.2.4Magnetic Flux - Calculations

7.2.5Motors

7.2.6Induced Potential

7.2.7Induced Potential 2

7.2.8Generator Effect

7.2.9Generator Effect 2

7.3Transformers

7.3.1Transformers

7.3.2Transformers 2

7.3.3Transformers 3

7.3.4Transformers - Calculations

7.3.5Transformers 2 - Calculations

7.3.6End of Topic Test - Magnetism

7.3.7Grade 9 - Transformers

7.3.8Exam-Style Questions - Magnetic Fields

8Astrophysics

8.1Astrophysics

8.1.1The Solar System

8.1.2The Solar System - Calculations

8.1.3Orbits

8.1.4Orbits HyperLearning

8.1.5Life Cycle of a Star

8.1.6The Universe

8.1.7End of Topic Test - Astrophysics

8.1.8Exam-Style Questions - Astrophysics

Jump to other topics