Wave amplitude in Hartlepool harbour

 

I was able to use binoculars to watch the swell against the depth marker on the harbour wall. It was in a mean position of 5.40m and max was 5.60m. The minimum was on a part of the scale that had been obliterated. The amplitude seems to be 20cm.

Keeping the sandwich hot

 

Once upon a time before lockdown we went to see the snowdrops at the Bake Off garden. We had a lovely lunch with wonderful cakes. They served the hot sandwiches in foil lined bags. The shiny surface should reflect infra-red radiation from the sandwich back inside the bag so making it harder for the sandwich to lose thermal energy. I should have looked harder to see if the paper outer was attached to the foil. A slight air gap would have increased the insulating properties. Paper doesn't conduct as well as metal so it wouldn't be as hot to hold. 

Full spectrum at Seaton Carew

 

These beach huts at Seaton Carew cover the visible spectrum very well. We physicists just get obsessed with the colours having the correct order of wavelength ... !

Thrust from a jet engine

 

This engine is on display at Watchtree, the result of a terrible crash some years ago. The data says a maximum thrust of 40kN. https://en.wikipedia.org/wiki/Panavia_Tornado says that the maximum mass of the loaded plane is about 20,000 kg. By  the Newton's 2nd Law equation F=ma, this gives a maximum acceleration of 2m/s/s. That doesn't sound very much and also ignores any counter forces like friction and drag. Following the references to source gets some very different data http://www.aerospaceweb.org/aircraft/bomber/tornado_ids/ It turns out that the plane had 2 engines and that the maximum thrust was 149.5kN. It doesn't say if that is total or for one engine, but let's take it as total. With no friction or drag, acceleration would be about 7.5m/s/s which is getting close to g.

Sandford Hydro data

 

https://www.lowcarbonhub.org/p/projects/sandford-hydro/ says that the hydro generates 1.6GWh every year and runs at 440kW. 1.6 x 10^9 divided by 365.25 divided by 24 = 182kW. This must be the average power with 440kW the peak, I suppose. 1.6 x 10^9 divided by 450 = 3500kWh roughly or a household electricity bill of around £400 a year.

Wetsuits

 

I hadn't worn a wetsuit before but was offered use of one for a dip in the sea. I have often wondered about why a swimming pool at 18 degrees feels much colder than the air at 18 degrees. I think that this is because the particles are closer in the water so it can conduct heat better. The wetsuit seems to work by trapping a layer of water and heating only that. As long as that remains next to the skin and is not replaced by cold water, thermal equilibrium is reached between the body and that layer of water so the body doesn't cool down further. The outer rubber layer means that the trapped layer of water loses heat slowly to the surrounding sea. It is well explained in detail at https://www.explainthatstuff.com/howwetsuitswork.html

Biggest person sits here

 

I was interested in this sign at the fair in Hunstanton. As the ride spins fast, the any object with inertial mass will tend to go in a straight line and will need a centripetal resultant force to pull it round in a circle. The heavier the person, the more force needed. Centripetal force = mass x radius x (angular velocity)^2. All objects wil have the same angular velocity. Putting the biggest mass on the biggest radius will mean a bigger centripetal force required. But more mass further out increases the moment of inertia of the ride which would mean that it will tend to go slower. We wondered whether the practical reason was that the heavier person would have more of a tendency to go straight on and would thus be more likely to crush the person outside them if sat on the inside seat.

Balancing the wheel

 

You can't usually see them because they are covered by the hub cap but car wheels have small masses added to the rim in certain places to make sure that the wheel is balanced. By that, we mean that as it rotates it doesn't wobble due to some parts being heavier than others. This is back to the moment of inertia issue from the last post. This article explains the physics very clearly https://en.wikipedia.org/wiki/Tire_balance This has good diagrams https://e-quipfix.co.uk/wheel-balancing-101-static-vs-dynamic-wheel-balancing/

Tandem rotors

 

I encountered this Osprey aeroplane at the mouth of the Nene where it comes out into the Wash. There is a military range on the far bank. It is a strange aircraft because the propellers that are seen here pointing forwards as normal can be swivelled to be vertical so it can operate like a twin rotor helicopter. It was doing that over the marsh when it was a long way off but I noticed through binoculars that the two rotors were rotating in opposite directions: one went clockwise and the other went anti-clockwise. The reason is this. One rotor would produce an equal an opposite torque that would spin the plane in the opposite direction to the rotor. Rotor would spin one way and the plane would spin the other. If the other rotor is doing the opposite then the two torques on the plane would be equal and opposite and the plane will not rotate.

The river flowing backwards in Wisbech

 

We were amazed to see the River Nene flowing the wrong way in Wisbech and then realised that although we were 10 miles inland, it was the tide. I'm told that spring tides with a strong wind to hold it can fill the river to the bottom of the bridge. I was wondering what affects the distance to which the tide flows inland. I found this https://en.wikipedia.org/wiki/Head_of_tide I went looking for the Normal Tidal Limit of the River Nene and found out that it is at least as far inland again, almost to Peterborough, at Dog in a Doublet https://www.waterways.org.uk/waterways/canals_rivers/river_nene/river_nene As yet, I cannot find anything on what factors affect the placing of the Normal Tidal Limit NTL on a river. A wider river would have more water from the sea moving in but a narrower river would possibly "squeeze" it more to get it further. 

Fire screen at Wainman House in Wisbech

 

I was wondering why there was a picture on a stand in front of the fireplace. Apparently it was to protect the faces of ladies. Coal fires produce a lot of infra-red radiation. In the past, ladies were expected to show that they had pale , untanned faces to show that they didn't have to work in the fields. Infra-red from the fire would cause the body to open the capillaries under the skin in the face and bring blood near the surface to lose thermal energy. The blood would make the face red. It is also said that the make-up was wax based and could melt. https://saffronwaldenmuseum.swmuseumsoc.org.uk/victorian-fire-screens/

Class 3 lever

 I've never thought much about the classes of lever. I have just got on with using the Principle of Moments to solve them. However, there's a lot of stuff out there about the types. The difference seems to be about the order in which you find the three elements. In the case of class 3, the effort and the pivot are both on one side of the pivot but the effort is nearer to the pivot. By the Principle of Moments, big effort force x small distance = small load force x big distance. It's a distance multiplier.

Cromarty Firth:how tall is that oil rig?

 

The Cromarty Firth is always full of oil platforms. They look big but how tall are they? Some workers got off the boat and climbed the scaffolding. I've circled where the last person had reached. On my screen the person is approximately 2mm high and the rig is 140mm tall. If we give a person as 2m tall it means the rig is 140m tall. 

A distance multiplier in Inverness

A fishing rod is a kind of lever. We normally use levers to increase the size of the force being applied. A small force from me (the effort) would move through a large distance but set up around a pivot so that on the other side a much larger force (the load) moves through a smaller distance. This would be called a force multiplier. The fishing rod in the photograph is a different type called a distance multiplier. Here the hand holding the rod puts in a big effort force but moves a small distance. At the other end of the rod, the distance moved by the load  is much bigger. I think the idea is in part that when casting you want the tip of the rod and thus the line to move through much larger distances than your wrist does. And I believe that a fishing rod is a third class lever, but that's another story.

Holding the sand together on the beach at Rosemarkie

The surface sand was very dry on the beach at Rosemarkie. Underneath was a layer of wetter sand that made good sandcastles. The dry sand made the pile on the right beyond the last decent sandcastle. So what does the water do? Even NASA have looked at this. It turns out that it is the surface tension of the water droplets that holds the grains together.
https://science.nasa.gov/science-news/science-at-nasa/2002/11jul_mgm#:~:text=Damp%20sand%20sticks%20together%20because,grain%2Dto%2Dgrain%20bridges.&text=Adding%20water%20to%20damp%20sand,sand%20can%20still%20puzzle%20researchers.

Forces on the fence at Chanonry Point

I was wondering about the physics of this fence post by the lighthouse on Chanonry point. I'm going to estimate som distances and assume the forces F2, F3, F4 and F5 are identical to simplify it. I'll call that idenical value F. Assuming the post is about 1 metre high and taking moments about the pivot, F1xsin50x1 = Fx1 + Fx0.75 + Fx0.5 + Fx0.25 which means F1= 3.26 x F. By this arrangement, the diagonal strand is not taking 4x the force, although there are 4 identical wires. The diagonal wire was also doubled up so each strand would only take half the force.

Pre-stressed concrete in Inverness

The plaque says that this is a pre-stressed concrete bridge. What that means is that it has steel bars going through it that are not just passive but have actually been tightened up so that they are squeezing the concrete. Concrete is incredibly strong under compression - it can been crushed with a huge force before it breaks. But it is not good when stretched under tension. The grains of sand come apart easily. By compressing it first, it makes sure that the concrete can carry a greater load than usual before reaching its limit for tension forces. This comes along the bottom side of the bridge.

Covid graph update for first week in August

 The numbers dying per day fell again this week but the data has become far more "noisy" as the total numbers have fallen. Small changes make a bigger difference.

Orion in Inverness

We found this office with the lovely gate in Inverness. The star in the bottom right hand corner is called Rigel. https://en.wikipedia.org/wiki/Rigel It is a big star with a high temperature and a large luminosity. The article says that it has a radius over 70 times that of the Sun and the surface temperature is 12100K. The surface temperature of the Sun is 5778K. Using Stefan's Law that says power output (luminosity) = sigma*A*T^4 where sigma is a constant and A is the surface area, it means that Rigel is  ((70^2)*(12100^4))/((1^2)*(5778^4)) = 94238 times brighter than the Sun which is within the range quoted in the article.

This week's Covid graph update

This week the 7-day rolling average for deaths is unchanged. You'll see that the point sticks out as an anomaly at the moment but no more than some previous data for last month. The R-squared value is down slightly but is still very high. This contains some explanation of what the R-squared number means https://statisticsbyjim.com/regression/interpret-r-squared-regression/