experiment on upthrust

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Harvard Natural Sciences Lecture Demonstrations

1 Oxford St Cambridge MA 02138 Science Center B-08A (617) 495-5824

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Archimedes' principle, what it shows.

Archimedes' principle states that the buoyant force or upthrust is equal to the weight of fluid displaced. An object with equal mass but a lower density occupies more volume so displaces more water; it therefore experiences a greater upthrust.

How it works

This demo compares the buoyant force acting on two 1kg masses, one of aluminum and one of brass. Each in turn is lowered into a beaker of water using a spring balance ( figure 1). The aluminum, having the lower density, experiences the greater upthrust and a reduction in weight from 10N to about 6N, compared to the brass whose weight drops to 8N.

figure 1. immersing the mass

Setting it up

Requirements are a 2 liter beaker, the two masses and a 20N spring scale. The masses will probably need cotton loops tied so they can hang from the balance.

Archimedes' original problem was to determine whether the king's crown was genuinely made of gold, and figured out how to solve the problem while taking a bath. The density of the metal determined the buoyant force and therefore the apparent weight loss when submerged.

Demo Subjects

Newtonian Mechanics Fluid Mechanics Oscillations and Waves Electricity and Magnetism Light and Optics Quantum Physics and Relativity Thermal Physics Condensed Matter Astronomy and Astrophysics Geophysics Chemical Behavior of Matter Mathematical Topics

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Floating and Upthrust

A partially submerged object (an object that’s not fully in a liquid) will experience greater pressure on the bottom surface than on the top surface. This creates a resultant force upwards. We call this force upthrust.

Upthrust = weight of liquid displaced

• The upthrust that acts on an object is equal to the weight of the liquid that has been forced away (displaced) by that object.

• If the object’s weight is equal to the upthrust, then the forces balance and the object will float in the liquid.

• If the object’s weight is greater than the upthrust, then the object will sink.

Depth Control of Submarine

Submarines use the balance between upthrust and weight to control their depth in water.

• When a submarine wants to sink, it fills its tanks with water to increase its weight.
• This means the submarine’s weight is greater than the upthrust and it sinks.

• When a submarine wants to come up to the surface, it fills its tanks with compressed air to reduce its weight.
• Weight becomes less than upthrust so the submarine rises.

1.1 Energy Changes

1.1.1 Energy Stores

1.1.2 Energy Storing

1.1.3 Internal Energy

1.1.4 Kinetic Energy Storage

1.1.5 Gravitational Potential Energy Storage

1.1.6 Elastic Potential Energy Storage

1.1.7 Calculating Changes in Energy

1.1.8 Changes in Kinetic Energy - Calculations

1.1.9 Changes in GPE - Calculations

1.1.10 Changes in EPE - Calculations

1.1.11 Energy Transfers

1.1.12 Energy Transfer Examples

1.1.13 Mechanical Work Done

1.1.14 Mechanical Work Done Equation

1.1.15 Mechanical Work - Calculations

1.1.16 Electrical Work Done

1.1.17 Power

1.1.18 Electrical Work Done- Calculations

1.2 Energy Losses & Efficiency

1.2.1 Energy Wastage

1.2.2 Efficiency

1.2.3 Reducing Energy Loss

1.2.4 Power & Energy Transfer

1.2.5 Efficiency - Calculations

1.2.6 Grade 9 - Energy & Efficiency

1.3 Energy Resources

1.3.1 Energy Resources

1.3.2 Fossil Fuels

1.3.3 Geothermal Energy

1.3.4 Wind Energy

1.3.5 Water Energy

1.3.6 Tidal Energy

1.3.7 Nuclear Energy

1.3.8 Solar Energy

1.3.9 Original Source of Energy

1.3.10 Non-Renewable and Renewable Resources

1.3.11 Uses of Energy Sources

1.3.12 Changing Electricity Use

1.3.13 Renewable Energy

1.3.14 End of Topic Test - Energy

1.3.15 Exam-Style Questions - Energy

2 Electricity

2.1 Electric Charge

2.1.1 Circuit Diagrams

2.1.2 Circuit Symbols

2.1.3 Current

2.1.4 Current Equation

2.1.5 Current - Calculations

2.1.6 Conductors

2.1.7 Potential Difference

2.1.8 Voltage Equation

2.1.9 Measurements in Circuit

2.1.10 Voltage - Calculations

2.2 Resistance & Electrical Work

2.2.1 Resistance

2.2.2 Resistance Graph

2.2.3 Diodes

2.2.4 LDRs and Thermistors

2.2.5 Electrical Work

2.2.6 Power

2.2.7 Ohm's Law

2.2.8 Resistance and Ohms Law - Calculations

2.2.9 Electrical Work - Calculations

2.3 Electric Circuits

2.3.1 Series Circuits

2.3.2 Resistors

2.3.3 Cells

2.3.4 Potential Difference

2.3.5 Series Circuits - Calculations

2.3.6 Parallel Circuits

2.3.7 Parallel Current

2.3.8 Parallel Resistance

2.3.9 Lights in Parallel

2.3.10 Parallel Circuits - Calculations

2.3.11 Grade 9 - Circuits

2.3.12 Exam-Style Questions - Electricity

2.4 Electricity in Homes

2.4.1 AC/DC

2.4.2 Mains Electricity

2.4.3 Power Ratings

2.4.4 National Grid

2.4.5 Domestic Uses - Calculations

2.4.6 Fuses & Circuit Breakers

2.4.7 Earthing

2.4.8 Dangers of the Live Wire

2.4.9 End of Topic Test - Electricity

2.5 Static Electricity

2.5.1 Electrical Charge

2.5.2 Charging an Object

2.5.3 Charged Objects

2.5.4 Static Electricity

2.5.5 Electric Fields

3 Particle Model of Matter

3.1 States of Matter

3.1.1 Atomic Model

3.1.2 Atomic Structure

3.1.3 Sub-Atomic Particles

3.1.4 Models of the Atom

3.1.5 Alpha Particles

3.1.6 Electron Arrangements

3.1.7 Density

3.1.8 Density Equation

3.1.9 Density and the Particle Model

3.1.10 Density - Calculations

3.1.11 Changes of State

3.1.12 Exam-Style Questions - Density

3.2.1 Internal Energy

3.2.2 Change in Thermal Energy

3.2.3 Specific Heat Capacity Experiment

3.2.4 Equation for Heat Capacity

3.2.5 Leslie's Cube

3.2.6 Internal Energy - Calculations

3.2.7 Melting and Boiling

3.2.8 Latent Heat

3.2.9 Energy Change for Change of State

3.2.10 Latent Heat - Calculations

3.2.11 Latent Heat Experiments

3.3 Particle Motion in Gases

3.3.1 States of Matter

3.3.2 Properties of Gases

3.3.3 Temperature Increase in a Gas

3.3.4 Work Done on a Gas

3.3.5 End of Topic Test - Particle Model of Matter

3.3.6 Grade 9 - Particle Model of Matter

3.3.7 Exam-Style Questions - Specific Heat Capacity

4 Atoms & Radiation

4.1.1 Atomic Model

4.1.2 Structure of an Atom

4.1.3 Sub-Atomic Particles

4.1.4 Alpha Particles

4.1.5 The Model of the Atom

4.1.6 Electron Arrangements

4.1.7 Proton and Nucleon

4.1.8 Atoms and Ions

4.1.9 Isotopes

4.1.10 Carbon Nuclides

4.1.11 Exam-Style Questions - Atomic Structure

4.2 Radiation

4.2.1 Radioactivity

4.2.2 Types of Radiation

4.2.3 Detection

4.2.4 Background Radiation

4.2.5 Types of Radioactive Emission

4.2.6 Ionising vs Penetration

4.2.7 Practical Applications of Radiation

4.2.8 Nuclear Fission

4.2.9 Nuclear Fusion

4.2.10 Radioactive Decay

4.2.11 Radioactive Decay Equations

4.2.12 Fission & Fusion Equations

4.2.13 Radio. decay equations - Calculations

4.2.14 Half Lives

4.2.15 Measuring Half Lives

4.2.16 Ionising Radiation

4.2.17 Half Life -Calculations

4.2.18 Safety Precautions

4.2.19 Uses for Isotopes With Different Half-lives

4.2.20 Radioactive Contamination and Irradiation

4.2.21 Peer Review

4.2.22 End of Topic Test - Atoms & Radiation

4.2.23 Grade 9 - Radiation

4.2.24 Exam-Style Questions - Radioactive Decay

5.1 Basics of Motion

5.1.1 Velocity

5.1.2 Average Speed

5.1.3 Adding Vectors

5.1.4 Acceleration

5.1.5 Distance vs Displacement

5.1.6 Contact and Non-Contact Forces

5.1.7 Distance-Time Graphs

5.1.8 Speed-Time Graphs

5.1.9 Average Speed - Calculations

5.1.10 Acceleration - Calculations

5.1.11 Uniform Acceleration - Calculations

5.1.12 Grade 9 - Motion

5.1.13 Exam-Style Questions - Motion

5.2.1 Mass and Inertia

5.2.2 Weight

5.2.3 Centre of Mass

5.2.4 Gravity - Calculations

5.2.5 Resultant Forces

5.2.6 Newton's First Law

5.2.7 Newton's Third Law

5.2.8 Newton Second Law - Calculations

5.2.9 Free Body Force Diagrams

5.2.10 Components of Forces

5.2.11 Free Body Diagrams - Calculations

5.2.12 Stretching a Spring

5.2.13 Hooke's Law and Equation

5.2.14 Spring Experiment

5.2.15 Hooke's Law - Calculations

5.2.16 Elastic Potential Energy

5.2.17 Elastic Potential - Calculations

5.2.18 Exam-Style Questions - Elastic Potential Energy

5.3 Effects of Forces

5.3.1 Acceleration

5.3.2 Air Resistance and Friction

5.3.3 Graphing Acceleration

5.3.4 Momentum

5.3.5 Momentum: Law of Conservation

5.3.6 Force and Momentum Change

5.3.7 Change in Momentum - Calculations

5.3.8 Momentum - Calculations

5.3.9 Moments

5.3.10 Equilibrium

5.3.11 Moments - Calculations

5.3.12 Circular Motion

5.3.13 Levers & Gears

5.3.14 Stopping Distance

5.3.15 Factors Affecting Stopping Distance

5.3.16 Decelerations

5.3.17 Stopping Distance - Calculations

5.4 Pressure

5.4.1 Pressure & Force on Container

5.4.2 Atmospheric Pressure

5.4.3 Liquid Pressure

5.4.4 Pressure - Calculations

5.4.5 Liquid Pressure - Calculations

5.4.6 Upthrust

5.4.7 Pressure Difference

5.4.8 End of Topic Test - Forces

5.4.9 Exam-Style Questions - Pressure

6.1 Wave Basics

6.1.1 Wave Basics

6.1.2 Wave Speed Formula

6.1.3 Wave Speed Equation

6.1.4 Wave Speed - Calculations

6.1.5 Wave Frequency Formula

6.1.6 Wavelength and Amplitude

6.1.7 Wave Frequency - Calculations

6.1.8 Transverse Waves

6.1.9 Longitudinal Wave

6.1.10 Required Practical - Ripple Tank

6.2 Waves at a Boundary

6.2.1 Waves at a Boundary

6.2.2 Reflection of Light

6.2.3 Refraction of Light

6.2.4 Internal Reflection

6.3 Sound Waves

6.3.1 Sound Waves

6.3.2 Sound Waves and our Ears

6.3.3 Speed of Sound

6.3.4 Speed of Sound Experiment

6.3.5 Sound as a Wave

6.3.6 Uses of Sound Waves: Ultrasound Waves

6.3.7 Uses of Sound Waves: Earthquakes

6.3.8 Sound Waves - Calculations

6.3.9 End of Topic Test - Introduction to Waves

6.3.10 Exam-Style Questions - Wave Speed

6.4 Electromagnetic Waves

6.4.1 Properties

6.4.2 Gamma Rays

6.4.3 X-Rays

6.4.4 UV Light

6.4.5 Infrared Radiation

6.4.6 Microwaves

6.4.7 Radio Waves

6.4.8 Properties 2

6.4.9 Visible Light

6.4.10 Specular and Diffuse Reflection

6.4.11 Colours

6.4.12 Grade 9 - Waves

6.5.1 Lenses

6.5.2 Convex Lens

6.5.3 Concave Lens

6.5.4 Lenses - Calculations

6.5.5 Images

6.5.6 Ray Diagrams

6.6 Heat & Radiation

6.6.1 Infrared Radiation

6.6.2 Radiation & Surface Colour

6.6.3 Surface Area & Temperature

6.6.4 Temperature

6.6.5 Greenhouse Effect

6.6.6 Energy Balance of the Earth

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

6.6.8 Exam-Style Questions - EM Radiation

7 Magnetism

7.1 Magnetism Basics

7.1.1 Magnetism

7.1.2 Magnetic Materials

7.1.3 Induced Magnetism

7.1.4 Magnetic Fields

7.1.5 Magnetic Field Patterns

7.2 Electromagnetism

7.2.1 The Magnetic Effect of a Current

7.2.2 Solenoid Field

7.2.3 Magnetic Field Strength

7.2.4 Uses of Electromagnets

7.2.5 Motor Effect

7.2.6 Magnetic Flux Equation

7.2.7 Magnetic Flux - Calculations

7.2.8 Electric Motors

7.2.9 Force Acting on a Coil in a Magnetic Field

7.2.10 Induced Potential Difference

7.2.11 Magnetic Field Direction

7.2.12 Forces Between Electricity and Magnets

7.2.13 AC/DC

7.2.14 Generator Effect

7.3 Transformers

7.3.1 Transformers

7.3.2 Transformer Equation

7.3.3 Step-Up and Step-Down Transformers

7.3.4 Principles of Transformer Operation

7.3.5 High-Voltage Transmission and Transformers

7.3.6 Energy in Transformers

7.3.7 Power Losses in Cables

7.3.8 Transformers - Calculations

7.3.9 Transformers 2 - Calculations

7.3.10 End of Topic Test - Magnetism

7.3.11 Grade 9 - Transformers

7.3.12 Exam-Style Questions - Magnetic Fields

8 Astrophysics

8.1 Astrophysics

8.1.1 The Solar System

8.1.2 The Sun

8.1.3 The Solar System - Calculations

8.1.4 Orbits

8.1.5 Stable Orbits

8.1.6 Orbits HyperLearning

8.1.7 Life Cycle of a Star

8.1.8 Creation of Elements

8.1.9 Red-shift

8.1.10 The Big Bang Theory

8.1.11 Gaps in Knowledge

8.1.12 End of Topic Test - Astrophysics

8.1.13 Exam-Style Questions - Astrophysics

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Liquid Pressure - Calculations

Pressure Difference

Materials: Upthrust

Fundamental concepts of upthrust.

Upthrust , also known as buoyancy , is a force experienced by an object when it is immersed, partly or fully, in a fluid.

It is the force exerted by a fluid that opposes the weight of the immersed object.

The principle behind upthrust is Archimedes’ principle , which states that a body immersed in fluid experiences a buoyant force equal to the weight of the fluid displaced by the body.

Upthrust is measured in Newtons (N) , the standard unit of force.

Determining Upthrust

The magnitude of upthrust depends on the density of the fluid , the volume of fluid displaced , and the gravitational field strength .

The upthrust (or buoyant force) can be calculated using the formula: Upthrust = Density of fluid x Volume displaced x gravitational field strength

This formula implies that upthrust is directly proportional to the volume of fluid displaced and the density of the fluid.

Upthrust and Density

The density of an object affects whether it will float, sink, or remain neutrally buoyant in a fluid.

If the density of the object is less than the density of the fluid, the object will float. This is due to the upward buoyant force being greater than the downward gravitational force.

If the density of the object is greater than the fluid, it will sink. This is because the downward gravitational force is greater than the upward buoyant force.

If the density of the object is equal to the density of the fluid, the object will remain neutrally buoyant. This happens when the upward buoyant force equals the downward gravitational force.

Real-World Applications of Upthrust

Understanding upthrust is vital for designing ships, submarines, hot air balloons and many other technologies that involve floating or sinking in a fluid.

For example, a ship floats because it displaces a volume of water that weighs more than the ship itself. The displaced water creates a buoyant force that balances the weight of the ship, allowing it to float.