5.2.3

Resultant Forces

Test yourself

Force and Acceleration

A force may cause a mass to accelerate. This acceleration can be a change in speed, a change in direction or a change in both speed and direction.

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Resultant force

  • The resultant force is the sum of all of the forces acting on an object.
  • The change in an object’s motion is caused by the resultant force.
  • If the forces acting on an object are unbalanced (not equal), it means that a resultant force is acting on the object.
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Resultant force equation

  • A resultant force causes an acceleration.
  • The acceleration can be calculated with the following equation:
    • Resultant force (F) = mass (m) x acceleration (a)
      • This is Newton's 2nd Law.

Newton’s 1st Law

Newton's 1st Law says that the velocity of an object will only change if a resultant force is acting on the object. This applies to a stationary (still) or moving object.

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Stationary (still)

  • If an object is stationary (not moving) and there is no resultant force acting on it, it will stay stationary.
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Moving

  • If an object is moving and there is no resultant force acting on it, the object will continue moving in the same direction at the same speed.
    • This means that the object will continue moving at the same velocity.
    • This also means that the velocity of an object will only change if a resultant force is acting on the object.

Jump to other topics

1Energy

1.1Energy Changes

1.1.1Energy Stores

1.1.2Calculating Changes in Energy

1.1.3Changes in Kinetic Energy - Calculations

1.1.4Changes in GPE - Calculations

1.1.5Changes in EPE - Calculations

1.1.6Energy Transfers

1.1.7Mechanical Work Done

1.1.8Mechanical Work - Calculations

1.1.9Electrical Work Done

1.1.10Electrical Work Done- Calculations

1.2Energy Losses & Efficiency

1.2.1Energy Losses & Efficiency

1.2.2Energy Losses & Efficiency 2

1.2.3Efficiency - Calculations

1.2.4Grade 9 - Energy & Efficiency

1.3Energy Resources

1.3.1Fossil Fuels & Geothermal Energy

1.3.2Wind & Water Energy Sources

1.3.3Nuclear & Solar Energy

1.3.4Sustainability

1.3.5Renewable Energy

1.3.6End of Topic Test - Energy

1.3.7Exam-Style Questions - Energy

2Electricity

2.1Electric Charge

2.1.1Circuit Diagrams & Components

2.1.2Current

2.1.3Current - Calculations

2.1.4Conductors

2.1.5Potential Difference

2.1.6Voltage - Calculations

2.2Resistance & Electrical Work

2.2.1Resistance

2.2.2Diodes, LDRs & Thermistors

2.2.3Electrical Work

2.2.4Ohm's Law

2.2.5Resistance and Ohms Law - Calculations

2.2.6Electrical Work - Calculations

2.3Electric Circuits

2.3.1Series Circuits

2.3.2Series Circuits 2

2.3.3Series Circuits - Calculations

2.3.4Parallel Circuits

2.3.5Parallel Circuits 2

2.3.6Parallel Circuits - Calculations

2.3.7Grade 9 - Circuits

2.3.8Exam-Style Questions - Electricity

2.4Electricity in Homes

2.4.1Domestic Uses

2.4.2Domestic Uses 2

2.4.3Domestic Uses - Calculations

2.4.4Electrical Safety

2.4.5Electrical Safety 2

2.4.6End of Topic Test - Electricity

2.5Static Electricity

2.5.1Static Electricity

2.5.2Static Electricity 2

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

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Gravity - Calculations

Newton Second Law - Calculations