Here is a link to some revision notes for the Our Dynamic Universe unit.

# our dynamic universe

## introducing special relativity…

We’ve been looking at Einstein’s special theory of relativity this week. Special relativity is tricky get get your head round. Let’s start with a video about the speed of light.

We watched this video in class, it follows Einstein’s thought process as he worked through his special theory of relativity.

**time dilation**and

**length contraction**. We’ll look at time dilation first.

###
**time dilation**

another take on special relativity and the twins paradox

…and the Glesga Physics version

**length contraction**

This video has helpful examples to explain length contraction.

Sometimes it’s easier to imagine we’re a stationary observer watching a fast moving object go whizzing past. For other situations, it’s better to put yourself into the same frame of reference as the moving object, so that ** everything else** appears to be moving quickly, while you sit still. The muon example in this video shows how an alternative perspective can work to our advantage in special relativity.

Another way to think about this alternative frame of reference is that it’s hard to measure distances when you yourself are moving really quickly. Think about it, you’d get tangled up in your measuring tape like an Andrex puppy.

###### image: trotonline.co.uk

It would be far easier to imagine you’re the one sitting still and all the objects are moving relative to your position, as if your train is stationary and it’s everything outside that’s moving. That keeps everything nice and tidy – including your measuring tape. Got to love Einstein’s postulates of special relativity.

###### image: mirror.co.uk

## H tension HW answers

I’ve marked your HW jotters and will hand them back during tomorrow’s lesson.

I’ll go over the main issues in class but many of you need to review the way you attempt tension questions; use a free body diagram and only use F=ma when you know the resultant force. These two videos should help.

HW question 4 from mr mackenzie on Vimeo.

Higher HW Q5 from mr mackenzie on Vimeo.

## higher homework

Your homework questions are attached. Please return to me by Wednesday 20th September.

## higher ODU revision notes

Here are some notes to help you prepare for the assessment later this week. There are also some useful resources on BBC Bitesize.

## Our Dynamic Universe summary notes

A set of summary notes for the 1st unit of Higher Physics is attached below. Don’t forget that BBC Bitesize and Scholar are also available for revision.

## Scholar tutorial for ODU unit assessment

The Scholar tutorial is on Monday 14th November, starting at 6pm. You can join the room from 5.30pm using the link on this page.

## Hubble discovers our universe is expanding

In the 1920s, Edwin Hubble had access to the Hooker telescope on Mount Wilson, Los Angeles. This was the largest telescope in the world at that time. His first breakthrough was the discovery of a cepheid variable star in the Andromeda nebula. This enabled him to calculate the distance to Andromeda and he quickly realised this was not a nebula but a galaxy outside the Milky Way.

This video follows his work.

Hubble – nebulae or galaxies? from mr mackenzie on Vimeo.

Hubble then turned his attention to other galaxies, looking for cepheid variable stars that would allow him to determine their distances from the Milky Way. He used redshift to calculate their recession velocity and plotted a graph against distance.

He found that the recession velocity (v) was directly proportional to distance (d). We can express this relationship as

where is the **Hubble constant**. Astronomers agree that the current value of the constant is

.

Since this is a SQA course, we need to convert into SI units – giving

In this video, Professor Jim Al-Khalili looks at Hubble’s work on the expanding universe.

Hubble’s discovery of the expanding universe from mr mackenzie on Vimeo.

Although he was American, Edwin Hubble transformed himself into a tea drinking, pipe smoking, tweed wearing Englishman during his time as a Rhodes Scholar at Oxford. He probably wouldn’t approve of this last video.

Unfortunately, astronomers were not eligible for the Nobel Prize for Physics. The rules have now been changed.

## redshift

more redshift

and Yoker Uni’s video about Doppler and stuff

While redshift can be used to tell us about the recession velocity of (non relativistic) galaxies, we also need to find a way to measure the *distance* to these galaxies. Astronomers have two main methods to measure these distances; parallax (more parallax here) and cepheid variable stars – there’s a Khan Academy video on cepheid variable stars.

using redshift to map the expanding universe from mr mackenzie on Vimeo.

## special relativity

Special relativity is tricky get get your head round. Let’s start with a video about the speed of light.

This video follows Einstein’s thought process as he worked through his special theory of relativity.

**time dilation**

A Tale of Two Twins from Oliver Luo on Vimeo.

another take on special relativity and the twins paradox

…and the Glesga Physics version

**length contraction**

This video has helpful examples to explain length contraction.

Sometimes it’s easier to imagine we’re a stationary observer watching a fast moving object go whizzing past. For other situations, it’s better to put yourself into the same frame of reference as the moving object, so that ** everything else** appears to be moving quickly, while you sit still. The muon example in this video shows how an alternative perspective can work to our advantage in Special Relativity.

Another way to think about this alternative frame of reference is that it’s hard to measure distances when you yourself are moving really quickly. Think about it, you’d get tangled up in your measuring tape like an Andrex puppy.

###### image: trotonline.co.uk

It would be far easier to imagine you’re the one sitting still and all the objects are moving relative to your position, as if your train is stationary and it’s everything outside that’s moving. That keeps everything nice and tidy – including your measuring tape. Got to love Einstein’s postulates of special relativity.

###### image: mirror.co.uk