The Expanding Universe Practical

A great little practical with washers, that was used as an exam question!

Try the following practical

http://www.schoolsobservatory.org.uk/astro/cosmos/uniball

expanding universe school observatory

Expanding Universe Experiment

To understand how the redshift of galaxies is due to the expansion of the Universe, try the following experiment.

You will need the following items:

  1. A round balloon (do not use a long, thin one).
  2. Some coloured stick-on dots (at least 5 different colours).
  3. A piece of string about 50cm long.
  4. A ruler.
  5. A stopwatch or other timer.

Step 1 : Setting Up

You will need to work in teams of at least two, one to blow up and hold the balloon and the other to make the measurements.

Before you start, draw a table for your results like the one below with the colours of your five dots in the 1st column:

Colour of DotFirst Distance D1 in cmSecond Distance D2 in cmChange in Distance        D2 – D1 in cmSpeed v in cm/second
Red    
Green    
Blue    
White    
Yellow    
Time to fully inflate the balloon:        seconds.

Step 2 : Making the Measurements

Putting dots on the small balloon

Blow up the balloon a little bit and hold the “nozzle” closed, but do not tie it up.

Stick your five dots onto the balloon. Try to spread them out over the whole balloon.

stick dots

Each of the dots represents a whole galaxy, with the surface of the balloon being the Universe that they exist in.

Choose one of the dots to be your “home”. You can choose any of them.

Step 3

Use string to measure the distance between two dots

measure dots

While one of you holds the balloon, the other one can use the string to measure the distance from your “home” dot to one of the other dots.

Now measure the string distance with a ruler.

When you have measured the distance, write it down in your table in the D1 column.

Step 4

Measure the distances from the “home” dot to all the other dots as well and fill in that column of the table.

Note: The distance from your “home” dot to itself is zero.

Step 5

Now carefully blow the balloon right up, using the stopwatch to time how long it takes. Write down the time in seconds.

Step 6

Now re-measure all the distances from “home” to all the other dots and write then down in the D2 column of your table. Don’t forget that the distance from your “home” dot to itself is zero.

You now need to work out the speed of each galaxy. Remember that:

Here, the Distance travelled is the difference between D1 and D2, so calculate D2 – D1 for each of our dots and write them in the 4th column on the table.

Step 7

The Time taken is the time to blow the balloon up. Work out the speed V for each dot and put it into the 5th column. Because your “home” dot has not moved, its speed will be zero.

Step 8

We are studying how the speed that galaxies seem to have gets larger for galaxies that are further away.

The best way to see this is to plot a graph showing the distance along the bottom axis and with the speed up the side.

This means that you need to plot a graph with axes like the one below:

speed v distance

Put the points for all your dots on the graph using D2 as the Distance.

Step 9 : What does it all mean ?

Use the ruler to draw a straight line that goes as close to as many of the points as possible (don’t forget the “home” dot!)

Think about the following questions and discuss them:

  • Are the speeds of all the dots the same?
  • If not, do they get faster or slower as they get further from the “home”?
  • What would be different if you had chosen a different “home”?
  • What would have been the same?
  • What do you think this tells you about the way that the Universe expands and the redshift of galaxies?

If you are not sure about some of the questions, can you think of a way changing the experiment to make them easier to answer?

 

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Updated November 2022

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’

PHYSICS WORLD ARTICLE DECEMBER 2009

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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