San Francisco de Paula, Science Department.
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      • Unit 1: Introduction to investigation >
        • How to write Lab Reports
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      • Unit 3: Classification of living things
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      • Unit 5: Nutrition I
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      • 7º PAI en español
      • Unit 1 - What do scientists do? >
        • How to write a lab report
        • SI Units
      • Unit 2 - The Earth in the Universe
      • Unit 3: How can we study living things >
        • Unit 3a - Living things
        • Unit 3b - The Diversity of Life >
          • Monera
          • Protists
          • Fungi
          • The Plant Kingdom
          • The Animal Kingdom
      • Unit 4 - Ecosystems & Biodiversity
      • Unit 5: The systems of the Earth >
        • Unit 5a - The Geosphere and the Atmosphere
        • Unit 5b - The hydrosphere and the Biosphere
      • Unit 6: Our changing home >
        • Unit 6a: Internal Geodynamics
        • Unit 6b: External Geodynamics
    • Laboratory & Tasks
  • MYP Year 8
    • Yr8 Syllabus & Assessment
    • Contents >
      • Units 1, 2 and 3 - Measuring Matters >
        • Unit 1 Physical quantities and Scientific Activity >
          • Converting Units
        • Unit 2 Matter and its Properties
        • Unit 3 Pure Substances and Mixtures >
          • Concentration and units (g/L, % mass)
      • Units 4 and 5 - Chemical Cooking >
        • Models of the Atom
        • Electronic structure of matter.
        • Periodic table (distribution of elements).
        • Chemical formulation
        • Molecular mass
        • Moles
        • Types of reactions
        • Lavoisier's law: Balancing of equations
        • Reaction rates: Factors that affect the speed of a reaction
      • Units 6, 7 and 8 - Move It! >
        • Unit 6 - Motion (URM)
        • Unit 6 - Motion (UARM)
        • Unit 7 - Forces and Mass
        • Unit 8 - Energy and Transformations
    • Laboratory & Tasks >
      • How to write a lab report
  • MYP Year 9
    • Yr9 Syllabus & Assessment
    • Contents >
      • Unit 1 - General organization of the human body, health and illness >
        • Human cells: levels of organisation
        • Health and types of diseases
        • Preventing diseases
        • The Immune System
        • Transplants
        • Addictive substances and associated substances
        • Complete Unit 1
      • Unit 2 - Nutrition >
        • Nutrition and nutrients
        • The Mediterranean diet
        • The anatomy and physiology of the digestive system
        • The anatomy and physiology of the circulatory system >
          • Revision quizzes
        • The anatomy and physiology of the respiratory system
        • The anatomy and physiology of the excretory system
        • Nutrition Documentaries
      • Unit 3 - Interaction and Coordination >
        • The function and anatomy of the nervous system
        • The endocrine system
      • Unit 4 - The reproductive system >
        • Anatomy and physiology of the human reproductive system.
        • Gametogenesis
        • Menstrual cycle
        • Fertilization
        • Infertility, contraception and STDs
      • Unit 5 - Genetics >
        • DNA and genetic modification
        • Cells and Inheritance
        • MORE ON MITOSIS VS MEIOSIS
        • Mendelian genetics
      • Unit 6 - Evolution >
        • Evolutionary theories
        • Evolution Simulators
      • EXTRA Unit 7 - Ecology and the environment >
        • Ecology
    • Laboratory & Tasks
  • MYP Year 10
    • Yr10 Syllabus
    • Contents >
      • Unit 0 - Formulation
      • Unit 1 - Scientific Activity
      • Unit 2 - Kinetic theory
      • The Atmosphere
      • Unit 3 - Mixtures and pures substances: Colligative properties
      • Unit 4 - The structure of matter
      • Unit 5 - Stoichiometry
      • Unit 6 - Redox Reactions
      • Unit 7 - Movement
      • Unit 8 - Forces
      • Unit 9 - Electricity
      • Unit 10 - Energy
    • Revision
    • Assessments and Lab Sessionss >
      • Assessments >
        • Criterion D - Water crisis
      • Session 1 - Paper balls
      • Sessions 2 - Properties of substances
      • Session 3 - Preparing a Schlenk tube
      • Session 4 - Gas constant
      • Session 5 - Colligative properties
      • Session 6 - Job´s method
      • Session 7 - Redox titration
      • Session 8 - UARM
      • Session 9 - Hooke´s Law
    • PISA questions
  • DP Biology SL
    • Contents >
      • Topic 1: Cell biology >
        • 1.1 Introduction to cells
        • 1.2 Ultrastructure of cells
        • 1.3 Membrane structure
        • 1.4 Membrane transport
        • 1.5 The origin of cells
        • 1.6 Cell division
      • Topic 2: Molecular biology >
        • 2.1 Molecules to metabolism
        • 2.2 Water
        • 2.3 Carbohydrates and lipids
        • 2.4 Proteins
        • 2.5 Enzymes
        • 2.6 Structure of DNA and RNA
        • 2.7 DNA replication, transcription and translation
        • 2.8 Cell respiration
        • 2.9 Photosynthesis
      • Topic 3: Genetics >
        • 3.1 Genes
        • 3.2 Chromosomes
        • 3.3 Meiosis
        • 3.4 Inheritance
        • 3.5 Genetic modification and biotechnology
      • Topic 4: Ecology >
        • 4.1 Species, communities and ecosystems
        • 4.2 Energy flow
        • 4.3 Carbon cycling
        • 4.4 Climate change
      • C: Ecology and conservation >
        • C.1 Species and communities
        • C.2 Communities and ecosystems
        • C.3 Impacts of humans on ecosystems
        • C.4 Conservation of biodiversity
      • Topic 5: Evolution and biodiversity >
        • 5.1 Evidence for evolution
        • 5.2 Natural selection
        • 5.3 Classification of biodiversity
        • 5.4 Cladistics
      • Topic 6: Human physiology >
        • 6.1 Digestion and absorption
        • 6.2 The blood system
        • 6.3 Defence against infectious disease
        • 6.4 Gas exchange
        • 6.5 Neurons and synapses
        • 6.6 Hormones, homeostasis and reproduction
    • Labs >
      • Statistical analysis
    • Previous to 2015 >
      • Topic 1: Statistical analysis
      • Topic 2: Cells >
        • 2.1 Cell theory
        • 2.2 Prokaryotic cells
        • 2.3 Eukaryotic cells
        • 2.4 Membranes
        • 2.5 Cell division
      • Option F: Microbes and biotechnology >
        • F1 Diversity of microbes
        • F2 Microbes and the environment
        • F3 Microbes and biotechnology
        • F4 Microbes and food production
      • Topic 5: Ecology and evolution >
        • 5.1 Communities and ecosystems
        • 5.2 The greenhouse effect
        • 5.3 Populations
        • 5.4 Evolution
        • 5.5 Classification
      • Option D: Evolution >
        • D1 Origin of life on Earth
        • D2 Species and speciation
        • D3 Human evolution
      • Topic 3: The chemistry of life >
        • 3.1 Chemical elements and water
        • 3.2 Carbohydrates, lipids and proteins
        • 3.3 DNA structure
        • 3.4 DNA replication
        • 3.5 Transcription and translation
        • 3.6 Enzymes
        • 3.7 Cell respiration
        • 3.8 Photosynthesis
        • TO DELETE
      • Topic 4: Genetics >
        • 4.1 Chromosomes, genes, alleles and mutations
        • 4.2 Meiosis
        • 4.3 Theoretical genetics
        • 4.4 Genetic engineering and biotechnology
      • Topic 6: Human health and physiology >
        • 6.1 Digestion
        • 6.2 The transport system
        • 6.3 Defence against infectious disease
        • 6.4 Gas exchange
        • 6.5 Nerves, hormones and homeostasis
        • 6.6 Reproduction
    • Tasks >
      • Databases
    • Documents
    • DP Biology Resources
    • Interesting links
  • Biología 12º
    • Bloque 1. Bioquímica
    • Bloque 2. Biología celular
    • Bloque 3. Genética y evolución
    • Bloque 4. Microbiología y biotecnología
    • Bloque 5. Inmunología
  • IB Biología NS
  • IB Chemistry HL
    • Contents >
      • Year 1 >
        • Topic 0 - Formulation
        • Topic 1 - Stoichiometric relationships
        • Topic 2 and 12 - Atomic structure
        • Topic 3 and 13 - Periodicity
        • Topic 4 and 14 - Chemical structure and bonding
        • Topic 5 and 15 - Energetics
        • Topic 10 and 20 - Organic chemistry
      • Year 2 >
        • Topic 6 and 16 - Chemical kinetics
        • Topic 7 and 17 - Equilibrium
        • Topic 8 and 18 - Acids and bases
        • Topic 9 and 19 - Redox processes
        • Topic 11 and 21 - Measurement and data processing
        • Option D - Medicinal chemistry
    • Lab work >
      • SFP Campus lab reports
      • Internal assessment structure
      • Internal Assessment examples
    • Nature of science
    • General revision
    • Selectividad
    • General information
    • Extended Essay
  • Other resources for students
    • Science Fair
    • Science essays >
      • How to Reference
    • Chemical formulation
    • Laboratory >
      • How to write a lab report
      • Microscopy
      • Excel for graphs and calculations >
        • Calculate the mean and SD
        • Drawing graphs
        • Add error bars to excel graphs
      • Lab videos!
    • Further Reading >
      • Women In Science
      • Infographics
    • Proyecto integrado
  • Department Home page
    • The International Baccalaureate
    • Conceptual learning
    • How will I be assessed?
    • Primary Science Club
    • Science Activities Noticeboard
  • MYP Year 6
    • Yr 6 Syllabus & Assessment
    • Contents >
      • Unit 1: Introduction to investigation >
        • How to write Lab Reports
      • Unit 2: Living things
      • Unit 3: Classification of living things
      • Unit 4: Fungi, Protists and Bacteria
      • Unit 5: Nutrition I
    • Laboratory and Tasks
  • MYP Year 7
    • Yr 7 Syllabus & Assessment
    • Contents >
      • 7º PAI en español
      • Unit 1 - What do scientists do? >
        • How to write a lab report
        • SI Units
      • Unit 2 - The Earth in the Universe
      • Unit 3: How can we study living things >
        • Unit 3a - Living things
        • Unit 3b - The Diversity of Life >
          • Monera
          • Protists
          • Fungi
          • The Plant Kingdom
          • The Animal Kingdom
      • Unit 4 - Ecosystems & Biodiversity
      • Unit 5: The systems of the Earth >
        • Unit 5a - The Geosphere and the Atmosphere
        • Unit 5b - The hydrosphere and the Biosphere
      • Unit 6: Our changing home >
        • Unit 6a: Internal Geodynamics
        • Unit 6b: External Geodynamics
    • Laboratory & Tasks
  • MYP Year 8
    • Yr8 Syllabus & Assessment
    • Contents >
      • Units 1, 2 and 3 - Measuring Matters >
        • Unit 1 Physical quantities and Scientific Activity >
          • Converting Units
        • Unit 2 Matter and its Properties
        • Unit 3 Pure Substances and Mixtures >
          • Concentration and units (g/L, % mass)
      • Units 4 and 5 - Chemical Cooking >
        • Models of the Atom
        • Electronic structure of matter.
        • Periodic table (distribution of elements).
        • Chemical formulation
        • Molecular mass
        • Moles
        • Types of reactions
        • Lavoisier's law: Balancing of equations
        • Reaction rates: Factors that affect the speed of a reaction
      • Units 6, 7 and 8 - Move It! >
        • Unit 6 - Motion (URM)
        • Unit 6 - Motion (UARM)
        • Unit 7 - Forces and Mass
        • Unit 8 - Energy and Transformations
    • Laboratory & Tasks >
      • How to write a lab report
  • MYP Year 9
    • Yr9 Syllabus & Assessment
    • Contents >
      • Unit 1 - General organization of the human body, health and illness >
        • Human cells: levels of organisation
        • Health and types of diseases
        • Preventing diseases
        • The Immune System
        • Transplants
        • Addictive substances and associated substances
        • Complete Unit 1
      • Unit 2 - Nutrition >
        • Nutrition and nutrients
        • The Mediterranean diet
        • The anatomy and physiology of the digestive system
        • The anatomy and physiology of the circulatory system >
          • Revision quizzes
        • The anatomy and physiology of the respiratory system
        • The anatomy and physiology of the excretory system
        • Nutrition Documentaries
      • Unit 3 - Interaction and Coordination >
        • The function and anatomy of the nervous system
        • The endocrine system
      • Unit 4 - The reproductive system >
        • Anatomy and physiology of the human reproductive system.
        • Gametogenesis
        • Menstrual cycle
        • Fertilization
        • Infertility, contraception and STDs
      • Unit 5 - Genetics >
        • DNA and genetic modification
        • Cells and Inheritance
        • MORE ON MITOSIS VS MEIOSIS
        • Mendelian genetics
      • Unit 6 - Evolution >
        • Evolutionary theories
        • Evolution Simulators
      • EXTRA Unit 7 - Ecology and the environment >
        • Ecology
    • Laboratory & Tasks
  • MYP Year 10
    • Yr10 Syllabus
    • Contents >
      • Unit 0 - Formulation
      • Unit 1 - Scientific Activity
      • Unit 2 - Kinetic theory
      • The Atmosphere
      • Unit 3 - Mixtures and pures substances: Colligative properties
      • Unit 4 - The structure of matter
      • Unit 5 - Stoichiometry
      • Unit 6 - Redox Reactions
      • Unit 7 - Movement
      • Unit 8 - Forces
      • Unit 9 - Electricity
      • Unit 10 - Energy
    • Revision
    • Assessments and Lab Sessionss >
      • Assessments >
        • Criterion D - Water crisis
      • Session 1 - Paper balls
      • Sessions 2 - Properties of substances
      • Session 3 - Preparing a Schlenk tube
      • Session 4 - Gas constant
      • Session 5 - Colligative properties
      • Session 6 - Job´s method
      • Session 7 - Redox titration
      • Session 8 - UARM
      • Session 9 - Hooke´s Law
    • PISA questions
  • DP Biology SL
    • Contents >
      • Topic 1: Cell biology >
        • 1.1 Introduction to cells
        • 1.2 Ultrastructure of cells
        • 1.3 Membrane structure
        • 1.4 Membrane transport
        • 1.5 The origin of cells
        • 1.6 Cell division
      • Topic 2: Molecular biology >
        • 2.1 Molecules to metabolism
        • 2.2 Water
        • 2.3 Carbohydrates and lipids
        • 2.4 Proteins
        • 2.5 Enzymes
        • 2.6 Structure of DNA and RNA
        • 2.7 DNA replication, transcription and translation
        • 2.8 Cell respiration
        • 2.9 Photosynthesis
      • Topic 3: Genetics >
        • 3.1 Genes
        • 3.2 Chromosomes
        • 3.3 Meiosis
        • 3.4 Inheritance
        • 3.5 Genetic modification and biotechnology
      • Topic 4: Ecology >
        • 4.1 Species, communities and ecosystems
        • 4.2 Energy flow
        • 4.3 Carbon cycling
        • 4.4 Climate change
      • C: Ecology and conservation >
        • C.1 Species and communities
        • C.2 Communities and ecosystems
        • C.3 Impacts of humans on ecosystems
        • C.4 Conservation of biodiversity
      • Topic 5: Evolution and biodiversity >
        • 5.1 Evidence for evolution
        • 5.2 Natural selection
        • 5.3 Classification of biodiversity
        • 5.4 Cladistics
      • Topic 6: Human physiology >
        • 6.1 Digestion and absorption
        • 6.2 The blood system
        • 6.3 Defence against infectious disease
        • 6.4 Gas exchange
        • 6.5 Neurons and synapses
        • 6.6 Hormones, homeostasis and reproduction
    • Labs >
      • Statistical analysis
    • Previous to 2015 >
      • Topic 1: Statistical analysis
      • Topic 2: Cells >
        • 2.1 Cell theory
        • 2.2 Prokaryotic cells
        • 2.3 Eukaryotic cells
        • 2.4 Membranes
        • 2.5 Cell division
      • Option F: Microbes and biotechnology >
        • F1 Diversity of microbes
        • F2 Microbes and the environment
        • F3 Microbes and biotechnology
        • F4 Microbes and food production
      • Topic 5: Ecology and evolution >
        • 5.1 Communities and ecosystems
        • 5.2 The greenhouse effect
        • 5.3 Populations
        • 5.4 Evolution
        • 5.5 Classification
      • Option D: Evolution >
        • D1 Origin of life on Earth
        • D2 Species and speciation
        • D3 Human evolution
      • Topic 3: The chemistry of life >
        • 3.1 Chemical elements and water
        • 3.2 Carbohydrates, lipids and proteins
        • 3.3 DNA structure
        • 3.4 DNA replication
        • 3.5 Transcription and translation
        • 3.6 Enzymes
        • 3.7 Cell respiration
        • 3.8 Photosynthesis
        • TO DELETE
      • Topic 4: Genetics >
        • 4.1 Chromosomes, genes, alleles and mutations
        • 4.2 Meiosis
        • 4.3 Theoretical genetics
        • 4.4 Genetic engineering and biotechnology
      • Topic 6: Human health and physiology >
        • 6.1 Digestion
        • 6.2 The transport system
        • 6.3 Defence against infectious disease
        • 6.4 Gas exchange
        • 6.5 Nerves, hormones and homeostasis
        • 6.6 Reproduction
    • Tasks >
      • Databases
    • Documents
    • DP Biology Resources
    • Interesting links
  • Biología 12º
    • Bloque 1. Bioquímica
    • Bloque 2. Biología celular
    • Bloque 3. Genética y evolución
    • Bloque 4. Microbiología y biotecnología
    • Bloque 5. Inmunología
  • IB Biología NS
  • IB Chemistry HL
    • Contents >
      • Year 1 >
        • Topic 0 - Formulation
        • Topic 1 - Stoichiometric relationships
        • Topic 2 and 12 - Atomic structure
        • Topic 3 and 13 - Periodicity
        • Topic 4 and 14 - Chemical structure and bonding
        • Topic 5 and 15 - Energetics
        • Topic 10 and 20 - Organic chemistry
      • Year 2 >
        • Topic 6 and 16 - Chemical kinetics
        • Topic 7 and 17 - Equilibrium
        • Topic 8 and 18 - Acids and bases
        • Topic 9 and 19 - Redox processes
        • Topic 11 and 21 - Measurement and data processing
        • Option D - Medicinal chemistry
    • Lab work >
      • SFP Campus lab reports
      • Internal assessment structure
      • Internal Assessment examples
    • Nature of science
    • General revision
    • Selectividad
    • General information
    • Extended Essay
  • Other resources for students
    • Science Fair
    • Science essays >
      • How to Reference
    • Chemical formulation
    • Laboratory >
      • How to write a lab report
      • Microscopy
      • Excel for graphs and calculations >
        • Calculate the mean and SD
        • Drawing graphs
        • Add error bars to excel graphs
      • Lab videos!
    • Further Reading >
      • Women In Science
      • Infographics
    • Proyecto integrado
San Francisco de Paula, Science Department.

Unit 7 - Forces

Picture
Key concept - Change- Past of an object in motion can be reconstructed and future foreseen on the basis of the current state and the forces acting upon it

Related concepts - Patterns and Motion- Motion and forces can be expressed in mathematical equations 

Global concept - Scientific and Technical Innovation- Constant parallel improvement of science and technology can provide answers to some of human questions about the universe..
Key words
  • Newton
  • force
  • body
  • gravity
  • mass
  • weight
  • hydrostatic
  • friction
  • normal
  • gravitational
  • weight
  • centripetal
  • acceleration
  • deformation 
  • pressure
  • surface area
  • pascals
  • atmospheres
  • hydraulic
  • Hooke´s law

Picture

7a. Newton´s 3 principles of motion

Principles of motion
1st - Unless acted on by a force, an object with remain at rest or at a constant velocity.
2nd - Force = mass x acceleration
3rd - When one body exerts a force on a second body, the second body exerts a force of equal magnitude and opposite direction on the first.
You will be required to use   F = m·a   along with the equations seen in unit 6. The only extra information required to calculate the force would be the mass of the object.
newton_laws-pogil_forces.pdf
File Size: 752 kb
File Type: pdf
Download File

Task 7a. Complete the following problems:
  1. A 1500 kg car starts from a standstill and accelerates to a velocity of 20 m/s in 10 s. It then hits a concrete wall. What is the force produced by this impact?
  2. Calculate the force exerted by a 100 g apple dropped from a height of 10 m. (This is a trick question)
  3. What will be the final velocity of a 500 kg motorbike that starts at a standstill, drives for 8 s and then produces a force of 500 N when it hits the back of a truck. (Luckily nobody is hurt!)
7a ANSWERS
task_7a_ans.pdf
File Size: 129 kb
File Type: pdf
Download File


7b. The law of universal gravitation

This relates the force of gravity (F), the universal gravitational constant (G), the masses of the 2 objects (m1 and m2 in kg) and the distance between them (d).
Picture
where G =
Picture
This law shows that the gravitational attraction between 2 bodies is:
  • Directly proportional to the mass of the objects
  • Inversely proportional to the distance squared
Task 7b: Consider the following theory questions using the equation above: (Hint: imagine the masses and distance both begin as 1 unit​)
​
1. Dawn wants to make as much money as possible by selling gold. Her plan involves buying gold by the weight at one altitude and then selling it at another altitude at the same price per weight. Should Dawn buy at a high altitude and sell at a low altitude or vice versa?

2. Suppose that two objects attract each other with a gravitational force of 16 units. If the distance between the two objects is doubled, what is the new force of attraction between the two objects?



3. Suppose that two objects attract each other with a gravitational force of 16 units. If the distance between the two objects is reduced in half, then what is the new force of attraction between the two objects?

4. Suppose that two objects attract each other with a gravitational force of 16 units. If the mass of both objects was doubled, and if the distance between the objects is also doubled, then what would be the new force of attraction between the two objects?
Picture
Extension:
When comparing mass and size data for the planets Earth and Jupiter, it is observed that Jupiter is about 300 times more massive than Earth. One might quickly conclude that an object on the surface of Jupiter would weigh 300 times more than on the surface of the Earth. For instance, one might expect a person who weighs 500 N on Earth would weigh 150000 N on thesurface of Jupiter. Yet this is not the case. In fact, a 500-N person on Earth weighs about 1500 N on the surface of Jupiter. Explain how this can be.
ANSWERS: 1. Buy at high altitudes and sell at low altitudes. 2. 4 units. 3. 64 units. 4. 16 units. 

7c. Types of forces

7c.i. Gravitational force

To calculate the force due to gravity here on Earth (weight or w) we can substitute G, d (radius of the Earth) and M (mass of the Earth) to give us:
Picture
where m = mass and
g = acceleration due to gravity
(9.8 N/kg    or    9.8 m/s^2)
As the units for g are in N/kg, this shows that the acceleration should be the same regardless of the mass (because for every kg of mass, there is a force of 1 N). This can be seen in the videos below.

7c.ii Normal force (Fnorm)

An object resting upon a surface is receiving a supporting force with a perpendicular angle to the inclination of the plane.

7c.iii. Friction (Ffrict)

This is the force exerted by a surface as an object tries to move across it. It is dependent on the nature of the 2 surfaces and can be calculated with the following equation:
Picture
Ffrict = µ · Fnorm
Where µ is the friction coefficient between the 2 materials.
Picture

7c.iv. Centripetal

The velocity vector of an object moving in a circle is always in the direction of the tangent. This means that in circular motion, the velocity vector is constantly changing direction. Therefore a force must be acting on it towards the centre of the circle.

We call this centripetal force​.
Task 7c.i: Which of the forces above could be found on the following (focus on the most significant of the forces above):
a. Mr Polko standing in the polideportivo.
b. An atom of iron in the direct centre of the Earth.
c. The International Space Station.
d. Mr Canning going down a slide.
Picture
Task 7cii:
Copy a snapshot of this GIF to your PCD and add arrows to the car (in 2 different positions) showing the 4 forces above.

7d. Pressure

Applying a force to an object can cause deformation. The amount of deformation depend on both the magnitude of the force and the surface area upon which it is applied.
Picture
Picture
Picture
Task 7di:
ai. What is the pressure produced by a force of 15000 N acting on an area of 5 m2.
ai. Explain the following demonstration in words. LINK
b. Which produces a greater pressure:
  • 10 N acting on 50 cm2
  • 1500 Pa
  • 200 N on 0.25 m2
  • 4 N on 200 mm2
c. A cylindrical tank with a compressible lid has a cross-sectional area of 40 cm2. What pressure is produced when a mass of 10 kg is placed on top.
ANSWERS: a. 3000 Pa;    b. 2000 Pa, 1500 Pa, 800 Pa, 20000 Pa​;   c. 24500 Pa

7e. The fundamental hydrostatic principle

In a vertical body of water, the internal pressure is due to the downwards force caused by the mass of water above it. So at a greater depth, there is more water above, therefore a greater downwards force and a high pressure. This is why a bottle of water with 3 holes in it will project water at 3 different distances (right).
Picture
This is described by the fundamental hydrostatic principle​. The interior pressure of a liquid of density d and depth h ​is:
p = h d g
Picture
Task 7f.i: 
  1. Explain what the diagram (left) is showing.
  2. Calculate the pressure exercised by water on a submarine at a depth of 300 m. Data: The density of sea water, d = 1030 kg/m3.
  3. Explain why the fundamental hydrostatic principle is important for divers? LINK

Extension: Why do fish eyes and stomach sometimes bulge out when they are pulled to the surface? VIDEO

Picture

7f. Pascal´s principle (hydraulic systems)

Due to the spacial particle arrangement of gases, they are easily compressed. As liquid particles are already touching each other, the are not easily compressed.
​This means that in an enclosed system, pressure is exerted equally and in all directions by a liquid.
This property if liquids can be used to explain its use in hydraulic (liquid) systems. A force used on small surface area at one end of the system can be transferred to make a large force on a large surface area.
Picture
Picture
Therefore, in a liquid:
Picture
Picture
Task 7ei:
a. Show how the 30 N force on the left piston creates a 150 N force on the right one?
b. What force on the left would be required to produced a force of 225 N on the right?
c. If an elephant with a mass of 2 tonnes stood on the right-hand side, what mass (kg) would be the minimum required on the left-hand side, to lift the elephant? 
ANSWERS:
i. F1/A1;    30/0.2 = F2/1.0;    F2 = 150 N
ii. 45 N
​iii. >400 kg

7g. Atmospheric physics

Atmospheric pressure​ - The pressure exerted by the atmosphere upon a body in it.
The first measurements of atmospheric pressure by Evangelista Torricelli were in units of mm Hg because of the experiment carried out. In it, a 1 m (1000 mm) was filled with mercury an inverted into a glass trough. The system reached equilibrium when the height of Hg dropped to 760 mm Hg as the pressure of the vertical Hg became equal to the pressure of the atmospheric pressure.
Picture



​This experiment can be used to calculate atmospheric pressure in Pa and atm.

760 mm Hg    =    101300 Pa    =    1 atm
Task 7gi: 
​a. Why might is this method of measuring pressure rarely used nowadays?
b. Suggest what would be different if this experiment was carried out at the top of Mt Everest.

7h. Archimedes principle

Archimedes discovered the idea that the ability of an object to float or sink in water id dependent on the amount of water displaced by that object.
  • If the weight of the water displaced is more that that of the object, then it floats.
  • If the weight of water is less, then the object will sink.
  • If the 2 weights are equal, then the object will be completely submerged but neither sink nor float (right).
Picture
Picture
The upward force of the water is called thrust (remember in a liquid the pressure acts in all directions) and can be calculated using the equation:
Fthrust = Vobject · dliquid · g
where d = density
and V = volume
If the force upwards is greater than the force downwards then the object will float.
Picture
A complex demonstration (left) shows immiscible liquids of different densities in layers. When different objects are dropped down the column, they stop sinking when then mass of the liquid displaced is more than that of the object.
Task 7h: 
​a. An object of unknown mass is place in a swimming pool full of milk. If the density of the milk is 1040 kg/m3 and the thrust created by the milk is 5096 N, what is the volume of the object? And in cm3?
b. A child gets into a pool, dislodging water with a weight of 300 N. What is the thrust receiving? What is the mass of the boy?
c. Why might the same boat sink further when travelling in a river compare to when it is travelling at sea?
Extension:
A. This is the cruise ship "Harmony of the Seas". Use to data below to calculate the minimum volume of the hull below the waterline that the ship must have.
​
Picture
B. ​Can you work out what is happening here? ​-->
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7i - Hooke´s Law

"When an elastic material is stretched, the extension (x) is directly proportional to the force (F) applied." 
F = k·x
In this formula, k is the extension constant and will depend on the material. This means that a graph of F against x should look like:
Picture
Picture
As straight lines have the general formula:  y = mx ​( where m is the gradient), The gradient from the graph will be the value of k​.

Revision

1. Mixed forces quiz
ProProfs Quiz- Unit 7 - Forces
​2. Unit 7 revision questions - LINK
​3. Mixed theory and problem-based questions - LINK
4.​ Unit 7 practice test
unit_7_practice_exam.docx
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File Type: docx
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unit_7_practice_exam_ans.docx
File Size: 379 kb
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