Inverse Square Law

A point light source  will spreads its energy equally in all directions. Therefore if you wanted to find all of the points in space where the energy was of the same intensity you would have to draw a sphere around the source point. The bigger the radius of the sphere the greater the ‘surface’ over which the energy was spread.

The relationship between radius and sphere surface area is an inverse square relationship. That means that intensity will depend on 1/r2. If you double the distance from the source the intensity will not halve but drop to a quarter of its value, tripling the distance will make the intensity drop to a ninth and so on.

Point sources of other quantities also obey the inverse square law.

  • gravitational force,
  • electric field,
  • light,
  • sound
  • electromagnetic radiation
  •  nuclear radiation

The key is “Are your sources point sources?”

An investigation can be completed into this.

 

Special Relativity & Web-based Research

Communicating Scientific Results

Here is a chance for you to practice some of the skills required for your Investigation. This task gives you some practice to help with your Researching Physics topic. It is to help you look at ways of communicating and think who you are communicating to.Log all the work that you do for this section in your Researching Physics Log Book.

Objective

You will look at the various ways in which findings can be presented, and appreciate the possibility of using other media such as video clips, articles, papers, posters etc.

Learning outcome

You will be more informed about the different ways in which one topic can be presented. You will begin to think about how to present your own work.

Learning activity

You can work independently or in groups. There are three different resources:

  1. A video clip entitled ‘Two postulates’ (http://www.youtube.com/watch?v=WdfnRWGgbd0).

    If you can’t read the file above it has been uploaded here as an MP4 file.

  2. A physicsworld article entitled ‘Slowed Light Breaks Record’ (http://physicsworld.com/cws/article/news/41246)
  3. The paper

‘On Velocities Beyond the Speed of Light c’ (On Velocities beyond the speed of light c.pdf) On Velocities beyond the Speed of Light

You should examine and discuss the three resources. Teachers should point out that even though the physics content may not all be at the students’ level of understanding, it is still possible to take information from it with their level of knowledge. This is emphasised by you completing the work below.

‘Two Postulates’

This clip discusses how to tell if an object is moving or not by way of an animation.

‘Slowed Light Breaks Record’

This is an article published in physicsworld in December 2009. It is not particularly long, although does contain a lot of information.

‘On Velocities Beyond the Speed of Light c’

This paper was published in 1998 from CERN. It has the more traditional scientific report structure and is a good example for you.

After completing the table on the sheet, you should find that all boxes are ticked – highlighting that even though the information is presented in different ways, all the resources contain what the students will have to put into their own reports.

There are many ways to present scientific findings. You might have written a report in the past but universities may ask you to present a poster of your work.

Here we will look at three different ways of presenting findings on special relativity.

On your own or in groups/pairs, have a look at the three examples of how findings on special relativity have been presented.

Copy and complete the table, either with a few notes or a tick or cross, to show if the example meets the criteria.

‘Two Postulates’ ‘Slowed Light Breaks Record’ ‘On Velocities Beyond the Speed of Light’
Is there mention of the objective for the investigation/experiment?
Is there information given on the experiment/s conducted?
Is there mention of the data (perhaps not all) and any analysis of the findings?
Does the article discuss the conclusion for the experiment/investigation?

Now you have looked at the three examples, ask yourself the following questions.

First impressions
  1. Was one resource more eye-catching than the others?
  2. Does one look like it will be easier to read/understand than the others?
  3. Which one looks most credible?
Down to the nitty gritty
  1. Which resource was the most interesting?
  2. Which one was the best presented?
  3. Which gave the most information?
  4. Did you need to understand everything mentioned to gain an understanding of the experiment?

Which format might you consider for your Communicating Physics investigation?

More information on Web-Based Research

Web-Based Research HApr16 A powerpoint presentation showing how to help you find viable websites

Web-Based Research Student Materials Some materials to give you advice on using websites.

Physics Web-Based Research Worksheets Material that you can work through to give you practice at completing web-based tasks.

 

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Measurement of acceleration due to gravity

Below are some links and documents for the Researching Physics dealing with measurement of the acceleration due to gravity.

http://practicalphysics.org/measurement-g-using-electronic-timer.html

http://www.practicalphysics.org/acceleration-due-gravity.html

 

 

 

 

 

 

 

 

 

https://revisionworld.com/a2-level-level-revision/physics/fields-0/gravitational-fields-0

The information below is based on the material found from the website above. TBC!

Fields

A field is a region of space where forces are exerted on objects with certain properties. Three types of field are considered:

  • gravitational fields affect anything that has mass
  • electric fields affect anything that has charge
  • magnetic fields affect permanent magnets and electric currents.

These three types of field have many similar properties and some important differences. There are key definitions and concepts that are common to all three types of field.

Gravitational fields

Newton realised that all objects with mass attract each other. This seems surprising, since any two objects placed close together on a desktop do not immediately move together according to Newton’s second law F=ma. The attractive force between them is tiny, and very much smaller than the frictional forces that oppose their motion.

Gravitational attractive forces between two objects only affect their motion when at least one of the objects is very massive. This explains why we are aware of the force that attracts us and other objects towards the Earth – the Earth is very massive. The mass of the Earth is about 6 × 1024 kg.

The diagram represents the Earth’s gravitational field.

The lines show the direction of the force that acts on a mass that is within the field.

This diagram shows that:

  • gravitational forces are always attractive – the Earth cannot repel any objects
  • the Earth’s gravitational pull acts towards the centre of the Earth
  • the Earth’s gravitational field is radial; the field lines become less concentrated with increasing distance from the Earth.

The force exerted on an object in a gravitational field depends on its position. The less concentrated the field lines, the smaller the force. If the gravitational field strength at any point is known, then the size of the force can be calculated.

The gravitational field strength, g, at any point in a gravitational field is the force per unit mass at that point

g=F/m

Close to the Earth g has the value of 9.8 Nkg-1

Gravitational field strength is a vector quantity, its direction is towards the object that causes the field.

Universal gravitation

Newton concluded, during his work, that the gravitational attractive force that exists between any two masses:

  • is proportional to each of the masses
  • is inversely proportional to the square of their distances apart.

Newton’s law of gravitation describes the gravitational force between two points. It can be written as

F=(GMm)/r2

Where

G is the universal gravitational constant and is equal to 6.67 × 10-11 N m2 kg-2  .   M and m are the magnitude of the masses and r is the separation between  the centre of the masses.

A point mass is one that has a radial field, like the Earth as shown in the diagram above.

Although the Earth is a large object, on the scale of the Universe it can be considered to be a point mass. The gravitational field strength at its centre is zero, since attractive forces pull equally in all directions. Beyond the surface of the Earth, the gravitational force on an object decreases with increasing distance. When the distance is measured from the centre of the Earth, the size of the force follows an inverse square law; doubling the distance from the centre of the Earth decreases the force to one quarter of the original value.  The two objects attract each other with equal sized forces and act in opposite directions. The variation of g with distance from the surface of the Earth is shown in the diagram.

g and G 

Newton’s law of gravitation can be used to work out the value of the force between any two objects. It can also be used to calculate the strength of the gravitational field due to a spherical mass such as the Earth or the Sun.

F=(GMm)/r2

As the value of F is also the weight then we can equate these two quantities, so that g not only equals W/m but also g=(GM)/r2 as below

Gravitational field strength is a property of any point in a field. It can be given a value whether or not a mass is placed at that point. Like gravitational force, beyond the surface of the Earth the value of g follows an inverse square law.

Because the inverse square law applies to values of g when the distance is measured from the centre of the Earth, there is little change in its value close to the Earth’s surface. Even when flying in an aircraft at a height of 10 000 m, the change in distance from the centre of the Earth is minimal, so there is no noticeable change in g. The radius of the Earth is about 6.4 × 106 m, so you would have to go much higher than aircraft-flying height for g to change by 1%.

The same symbol g is used to represent:

  • gravitational field strength
  • free-fall acceleration.

These are not two separate quantities, but two different names for the same quantity. Gravitational field strength, g, is defined as the force per unit mass, g = F/m.

From Newton’s second law and the definition of the newton, free-fall acceleration, g, is also equal to the gravitational force per unit mass. The units of gravitational field strength, N kg–1, and free-fall acceleration, m s–2, are also equivalent.

 

Exoplanets

RP_Exoplanets

A set of focus questions for you to look over before planning your investigation. It is important that any work you complete on the theory is about Physics and not any other subject!

Exoplanets 1

Exoplanets 2

Exoplanets 3

Exoplanets 4

Exoplanets 5

Exoplanets 6

Exoplanets 7

Exoplanets 8

Exoplanets master

Exoplanets Teachers’ Guide

Detecting Exoplanets

file_42552 The search for planets beyond our solar system, a document produced by the Institute of Physics on Exoplanets.

Kepler[1]

plan-the-rp-unit-invest_2 Some information about the practicals that can be completed.

Earthquakes

Credit: U.S. Geological Survey Department of the Interior/USGS U.S. Geological Survey/photographer unknown

A set of focus questions for you to look over before planning your investigation. It is important that any work you complete on the theory is about Physics and not Geography, Geology or any other subject!

Earthquakes 1

Earthquakes 2

Earthquakes 3

Earthquakes 4

Researching Physics Earthquakes

Researching Physics

The information for the Higher Assignment can be found in the document from the link below.   http://www.sqa.org.uk/files_ccc/GAInfo_HigherPhysics.pdf

This document gives you detailed guidance on how to complete your assignment write up, what it must include and how to lay this out. It ought to be read in conjunction with the understanding standards examples contained at the link below

http://www.understandingstandards.org.uk/Subjects/Physics

Read these documents carefully, they are vital for your write up. Make sure you clearly understand what they require of you. Your assignment is worth 17% and that is the difference between an A and a C grade, or a B and a D or F!

“But the reason I call myself by my childhood name is to remind myself that a scientist must also be absolutely like a child. If he sees a thing, he must say that he sees it, whether it was what he thought he was going to see or not. See first, think later, then test. But always see first. Otherwise you will only see what you were expecting.”
Douglas Adams, So Long, and Thanks for All the Fish

In a selection of posts Mrs Physics will supply some recommended reading for some potential Higher Investigations and Research Topics. If there is something that you were particularly interested in make sure that you have a discussion with your Physics teacher to ensure it meets the requirements for the unit.

Unit outline

CfE Unit H Physics Researching Physics

The aim of this Unit is to develop skills relevant to undertaking research in Physics. You will plan and undertake a practical investigation and analyse results.

SQA Mark scheme and General Information

General Info_HigherPhysics Sept 16

The Unit offers opportunities for collaborative and independent learning. You will develop knowledge and skills associated with collecting, recording and processing information from a number of different sources. Equipped with knowledge of standard laboratory apparatus, you will plan and undertake a practical investigation related to a chosen physics topic.

Learners who complete this Unit will be able to:

1 Apply skills of scientific inquiry and draw on knowledge and understanding to research the underlying physics of a chosen topic

2 Apply skills of scientific inquiry to investigate, through experimentation, the underlying physics of a chosen topic

This Unit is a mandatory Unit of the Higher Physics Course and is also available as a free-standing Unit. 

“Everything must be taken into account. If the fact will not fit the theory—let the theory go.” Agatha Christie, The Mysterious Affair at Styles.

 

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