Chapter 9

Forces

Application of Forces and Transfer of Energy

• Chapter 9 overview.

Objectives

By the end of the unit, you will be able to:

• Identify the effect of forces in daily life.

• Define contact force and non-contact force.

• Describe effects of forces, such as changing the shape/size, stopping moving objects.

• Identify examples of contact and non-contact forces.

• Predict effects of contact and non-contact forces on objects.

Objectives (Continued)

• Compare mass and weight.

• Measure mass and force using S.I. units.

• Relate pressure to force and area with everyday examples.

• Describe how some daily live phenomena are associated with atmospheric pressure and pressure due to liquid

  

What is a Force?

• Natural disaster like earthquakes, volcanic eruption and tsunami demonstrate destructive forces in nature

• Forces in natures also gives rise to beautiful landscapes like Twelve Apostles in Australia.

Definition of Force

• A force is defined as a push or pull.

• The SI unit for force is Newton (N).

Examples of Forces

• Opening a window or door involves applying force via the handle.

• Pressing a button in a lift uses fingers to apply push.

• Squeezing a tube of toothpaste employs finger pressure.

• Turning on a tap requires turning or pulling the lever.

Types of Forces – Contact Forces

Frictional Force

• Occurs when two objects are in contact with each other.

• Rough surfaces have more friction;

• Smooth surfaces have less friction.

Types of Forces – Non-Contact Forces

Magnetic Force

• Occurs when you have a force exerted by a magnet on magnetic material.

• Like poles of the magnet will experience a repulsive force (repel).

• Unlike poles of the magnet will experience an attractive force

  

Electrostatic Force

• Occurs when you have like and unlike charges placed near each other

• Like charges will have a repulsive force

• Unlike charges will have an attractive force

Types of Forces – Non-Contact Forces

Gravitational Force

• It is a force where objects are attracted to the planet

• Due to gravity, any matter that has mass will have a downward force called weight.

How is friction useful in our daily lives?

• Parachuting: The parachute is large piece of nylon that produces a large frictional force with the air. This reduces the speed of the parachutist’s fall.

• Lighting a Fire: Matchsticks are ignited by friction between moving objects. The head of the matchstick rubs against the rough sides of the matchstick box, causing heat. This enables the head to catch fire

• Writing on Paper: When we write with a pencil, the pencil’s tip rubs against the rough surface of the paper. Friction transfers carbon lead onto the paper and also allows us to grip the pencil.

• Walking: When we walk, the rough soles of ur shoes or feet rub against the ground. Friction between our feet and th

Mass and Weight

• Introduction to the concepts of mass and weight.

What is Mass?

• Mass is the amount of matter (substance) in thebody

Mass and Weight Examples

• Mass on the moon = 60 kg; Weight on the moon = 100 N.

• Mass on Earth = 60 kg; Weight on Earth = 600 N.

Why does the man weigh less on the moon as compared to the Earth?

• It is because the gravitational field on the moon is less than that on the Earth. Hence, even though the mass remains the same, the weight is different.

Effect of Gravity on Mass

• Mass is the amount of matter in our body

• Under the influence of gravity, all objects that has mass exerts a force.

• This force is called gravitational force (or weight)
  

Definition of Weight

• It is the amount of gravitational force acting on an object.

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Differences between Mass and Weight

Measuring Force (Weight)

• We use a spring balance to measure force. There are two types of spring balances

• 

• The spring in an extension spring balance stretches when a pulling force acts on it.

• 

• The spring in a compression spring balance compresses when a pushing force acts on it.

• A pointer attached to the spring indicates the amount of force acting on the spring

Effects of Forces

• Change in state of motion

  • ,Change direction of object

  • Slow down or increase speed of object

  • Start an object moving

  • stop a moving object

• Produce a turning effect (moment).

• Change shape and size of the object (cannot change the mass of an object).

• Change in pressure on an object.

Effect of gravitational force

• Ocean tides

• Gravitational force is responsible for the movement ofhigh and low tides in harbors, ports and coastal areas

• The tides are caused partly by the moon’s gravity pullingon the waters of the ocean.

Turning Effect of Forces (Moments)

• Discussion on where it is easiest to open a door (hinge).

• 

Definition of Moment

• A moment is the turning effect of forces

• :For the turning effect of forces to occur, three things need to be present:

• Pivot

• Force

• Perpendicular distance between force and pivot

• 

Importance of Moments

• Through the turning effect of the force (moments),we are able to move the object using less force.

• The larger the perpendicular distance between the force and pivot, the lesser the force required to produce the moment to move the object.

Examples of Moments

• Crowbar: A person applies a force on the handle of a crowbar. The crowbar turns and pulls out the nail from the wooden plank.

• 

• Fishing Rod:A person applies a large force on the fishing rod handle to lift the fishing rod. The fish that is caught at the other end of the rod moves over a large distance.

• 

Definition of Pressure

• Pressure is the amount of force acting perpendicularly per unit area.

• Pressure can be calculated by measuring the amount of the force on the surface and the area of the surface

• Formula: Pressure = Force (N) / Area (m²)

Pressure in Everyday Life

• Fingers apply force on a pin’s head, generating pressure to pierce surfaces.

• Cutting edges of knives have small surface areas, hence high pressure allows cutting.

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Atmospheric Pressure Overview

• Earth is surrounded by air, creating pressure through the weight of air particles.

• Height affects atmospheric pressure due to fewer air particles.

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Application of Suction Cups

• Suction cups utilize atmospheric pressure to adhere to surfaces, working on a principle of pressure difference.

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Suction Cup Functionality

• When air is pumped out, lower pressure inside the suction cup causes it to stick via atmospheric pressure acting from outside.

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Liquid Pressure Overview

• Immersion creates pressure around an object from surrounding liquid; deeper immersion increases this pressure.

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Practical Activity

• Practical 9.3.2 explores pressure measurements.

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Energy Transfer and Work Done

• Introduction to concepts of energy transfer and work.

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Objectives of the Unit

By the end of the unit, you will be able to:

• Identify energy as the ability to do work.

• Understand that work occurs when an object moves with applied force.

• Recognize energy transfer during work.

• Acknowledge energy conservation in transformations.

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Additional Objectives

• State S.I. unit of work as joule.

• Compare situations where work is done vs. not done.

• Appreciate energy sources and environmental impacts.

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Unit Organization

• Four main sub-units:

1. Types of energy

2. Conservation of energy

3. Work done

4. Sources of energy

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Understanding Work Done

• Work done equals product of force and distance moved: Work Done = F x d (where F = force in Newtons, d = distance in meters).

• Unit of work is joule (J).

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Conditions for Work Done

• Work occurs only when energy is transferred.

• Conditions: Force must act on an object, and the object must move in the direction of the force.

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Example of Work Done

• Marie lifts a box applying a force; work done calculated based on force and distance.

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Another Example of Work Done

• Marie holds a basket; despite applying force, no work is done as there is no movement.

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Third Example of Work Done

• Marie carries a basket; still no work done as the force does not align with the distance moved.

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Practice Activity

• Group work on calculating work done.

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Conservation of Energy Overview

• Introduction to the concept of energy as the ability to do work; S.I. unit is joule.

• Different types of energy recognized.

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Types of Potential Energy

• Stored energy types include gravitational, elastic, and chemical potential energy.

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Gravitational Potential Energy

• Gravitational potential energy is determined by height; formula: GPE = mgh (m = mass, g = acceleration due to gravity, h = height).

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Elastic Potential Energy

• Energy stored in materials when compressed or stretched.

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Chemical Potential Energy

• Stored in chemicals/compounds; released for work during reactions.

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Potential Energy in Action

• Real-life applications of potential energy.

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Kinetic Energy Overview

• Energy of motion; faster objects have higher kinetic energy.

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Summary of Other Energy Forms

• Summary includes light, electrical, thermal, and sound energy.

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Conservation of Energy Principle

• Energy cannot be created or destroyed, only transformed between forms.

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Energy Conversion Example

• Conversion examples from battery (chemical to electrical to heat/light).

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Energy and Motion Example

• Energy conversion when a ball rolls down a slope releases potential energy into kinetic energy.

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Practice Time for Scenarios

• Discuss energy conversion scenarios.

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Sources of Energy Overview

• Seven sources of energy include fossil fuels, solar, hydroelectric, wind, geothermal, biofuels, and nuclear energy.

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Classification of Energy Sources

• Broad classification into renewable and non-renewable sources.

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Non-Renewable Sources

• Non-renewable sources like oil, coal, and natural gas are limited and detrimental to the environment.

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Fossil Fuels Overview

• Fossil fuels take millions of years to form; rapid consumption threatens future supply.

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Generating Electricity from Fossil Fuels

• Overview of the electricity production process from fossil fuels.

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Energy Conversion in Power Stations

• Energy transformations in power stations detailed from chemical to electrical energy.

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Problems with Fossil Fuels

• Environmental and health issues from fossil fuel use, including global warming and pollution.

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Renewable Energy Alternatives

• Exploration of renewable energy technologies to mitigate fossil fuel use.

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Solar Energy Technology

• Solar energy generation using photovoltaic cells.

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Environmental Impact of Solar Energy

• Clean energy with minimal pollutants, but high costs associated with solar panels.

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Hydroelectric Energy Overview

• Water flow used for energy generation.

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Wind Energy Overview

• Conversion of wind's kinetic energy into electricity using turbines.

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Environmental Impacts of Wind Energy

• Potential dangers to wildlife and noise pollution concerns.

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Geothermal Energy Overview

• Derived from hot underground rocks, harnessed for energy use.

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Environmental Impact of Geothermal Energy

• Risks of extracting harmful substances and potential land subsidence.

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Biofuels Overview

• Derived from organic matter; similar energy release as fossil fuels.

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Environmental Impact of Biofuels

• Contributions to global warming mitigated somewhat through carbon uptake during growth.

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Nuclear Energy Overview

• Derived from the nucleus of atoms; energy produced through nuclear fission.

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Environmental Impact of Nuclear Energy

• Clean energy with waste management concerns and potential hazards.

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Conclusion of Energy Sources

• Review of energy sources and their impacts on environment and sustainability.

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Activity Practice Questions

• Structured practice questions on energy concepts and resources for further exploration.