Diffraction round a rock on Haweswater

 

Part of the old landscape was just above water level at Haweswater today. If you want to see which bit it was, you'll need to check the photographs here. The wind was driving plane waves towards it. The wavelength was roughly the size of the rock so the waves diffracted to fill in the area behind the rock that would have been in the "shadow".

A sundial with seats in Porthcawl

 I'm always a sucker for a new sundial design. I really liked this one with seats in Porthcawl.

Could this be wad?

 We climbed up to the lowest level at the Seathwaite Graphite Mine - graphite being called wad in the old days.

These two rocks were lying around and seemed to be dark grey and crystalline. Could they be wad? The one on the left drew a nice line like a pencil. It had a measurable resistance with the contacts quite close that fluctuated between 500 and 1000 Ohms.

I had no pencil so back in Wigton I checked the resistance of a short pencil "lead"

So the pencil graphite has a much lower resistance but every other rock I've tested has a resistance so high that it can't be measured on the scale. It might well have been graphite.

This is what 1500 years looks like - Borrowdale Yews

 

I found a lovely guide to ageing trees from their girth here. Sadly I didn't measure the girth of the Borrowdale Yews but Internet cheating here says 7.56m at present but previously larger. This would tie in with the implications of the "poor ground and some exposure" section of the first document. Not as accurate but easier than counting tree rings in my opinion!

Finding the SHC of copper coins by a heat transfer method

 

We weighed ten 2p pieces. We got two polystyrene cups. We labelled them A and B. We put the coins into B. We measured 60 cubic centimetres of cold water into each and marked the level. We emptied the water and then added fresh boiling water from a kettle up to the mark. A is a control that tells us what the water temperature would be without the coins. When A reaches the highest temperature, take temperature in B as well. The difference is delta(theta) for the water. Calculate energy transferred to the coins from the water by 0.060kg x 4200 J/kgoC x delta(theta). This is the energy used to heat the coins up from room temperature, which also needs to be measured. Mass of coins in kg x unknown SHC x temp rise of coins = energy that went out of the water.

Syenite at Scale Force (Red Pike)??

 

On page 8 of the Red Pike (Buttermere) chapter, Wainwright says that the subsoil next to Scale Force is coloured red due to syenite. I can find no up-to-date reference to syenite in England other than ones that seem to take it from Wainwright. It turns out that syenite is like granite but has much less quartz. see this There are other difference. The granite in Ennerdale is a redder granite. However, BGS seem to list several sites in Scotland, the nearest of which in the Nith Valley might be visible from my kitchen window! I did find Adam Sedgwick's The Geology of the Lake District on Google Books. This was published in 1853. On page 44 he calls the Ennerdale rock "syenite" as distinct from Eskdale Granite. This might well be Wainwright's source. I need to do more research on this.

Component of weight on a ploughing boulder

 I've posted about ploughing boulders before. This is a very good example on the slopes above Tray Dub in Langstrath.

The pole is 90cm long. The estimated dimensions of the boulder are 2m x 1m x 1m. Density of volcanic rock like this is 2500 kg per cubic metre so mass is estimated at 5000 kg. This is a steep slope to walk on; that usually means 30 degrees. Thus component of weight down the slope shown is 5000 x g x sin(30) = 25kN to 2sf. Most of the time friction is enough to hold it but some winters the freeze-thaw means friction must be less than this.

Lilac and potassium flames

 

Mrs B's lilac bush is in full bloom and reminded me that the official description of the colour of potassium in a flame test is lilac.

I know that this is because electrons are excited and go up energy levels. When they de-excite, they emit photons and the wavelength depends on the set up of the electron levels in the atom. The colour tells us something about the electron energy levels in potassium atoms. I found this brilliant answer. I have missed telling my classes that it is a flame test to use the electrons available to turn the vaporised ions back into atoms so that the electrons in the atoms can then go up and down the levels. I'm also interested that there is deep red here that I cannot see.

Lower pressure means lower power

 Having calculated the power of my gas stove, I boiled a litre of water another three times. The time taken got longer and longer. This must be to do with lower pressure reducing the gas flow rate. I assume that a part empty cannister has lower internal pressure than a full one and adiabatic cooling also reduces the pressure. Here's the data starting with my first go:

Second reading is 33% bigger than the first.

16% bigger than the previous.

This is now another 47% bigger.

Scale Force

 

Scale Force is the highest waterfall in the district. The name is very Physics. We read from scales and talk about scale divisions. I wondered what could be done with the force of the water. Now Newton's Second Law can be say that force is equated with the rate of change of momentum which for a stream of water hitting an obstacle becomes the speed at which it hits x mass flow rate. Technically the speed at which the waterfall hits the bottom could be calculated by suvat but the air resistance is likely to affect that. So I favour putting weighing scales under the falls to record the force - hence Scale Force. Then record volume flow rate by timing how long a bucket takes to fill. Mass flow rate = volume flow rate x density of water. These readings would allow speed to impact to be calculated and that could be compared to the suvat value.

Finding the power of my camping stove

 I poured one litre of water into the kettle and timed how long it took to boil with a full gas cannister.

The mass of water was 1kg. The water was at ambient temperature of about 10 degrees Celsius and reached 100 degrees Celsius for boiling. Energy absorbed is m.c.delta(theta) = 1 x 4200 x 90 = 378000J.

It took 7 minutes 25 seconds or 445 seconds to boil. So the effective power of the stove in this circumstance is 378000/445 = 850W. I say "effective" power because I'm only interested in the useful energy transformation; the energy wasted heating the surroundings is of no interest here.

Mapping circular motion onto linear SHM

 

Yesterday's toy reminded me of this experiment I used to do. I stuck a table tennis ball onto a turntable and projected the shadow onto the screen. As the turntable rotates, the shadow appears to perform SHM.

Unfortunately the letter labels on the schematic diagram below don't correspond to the photo above

But notice that a 90 degree rotation takes the shadow from the middle to the edge so the middle and the amplitude of the SHM have a phase difference of 90 degrees. 

An eccentric toy

 When this plastic car is pushed along, the grey bits on the front and back rock from side to side to give the impression of driving over rough ground.

The effect is achieved by spikes on the axle.

When the spike is vertical it pushes up that side of the bonnet. On each end of the axle, there are two spikes set 180 degrees out. But the ones at the bottom of the axle in the photo are shifted by 90 degrees from the ones at the top. So are they out of phase by 90 degrees? Well, when one side of the bonnet is completely up, the other side is completely down. That is 180 degrees out of phase. It is interesting that the spikes need to be 90 degrees out to give 180 degree phase difference. That is probably about projecting from circular motion onto a linear motion.