Inertia experiments 3 and 4

In these experiments, a tub full of sand and an empty tub are taped to the top of two trolleys. In one experiment you push the trolleys away from you, one with your left hand and one with your right hand. You catch them with elastic bands. The heavier one stretches the elastic band more, showing that a bigger external force is needed to effect the change in motion. You then use the elastic bands to pull them towards you instead and the same thing happens. The bigger the mass, the bigger the external force needed to change the motion. This is INERTIA.

Inertia experiment 2

The two margarine tubs are supposed to look identical but one is full of sand and is much heavier. Pull the paper gently - one with each hand - and you can feel the difference but both move. Then give the papers a sudden tug.

The heavy one stays where it is but the light one is more likely to fall over. The heavy object has inertia. If an external force acts it is more likely to carry on doing what it was doing beforehand - in this case, staying still. Newton's First Law again.

Inertia experiment 1

In this experiment a trolley is allowed to roll down a ramp so that it hits a solid barrier at the bottom. The marble is not pressed in to the plasticine; it rests loose on top. The trolley carries on down the ramp in a straight line. When it hits the barrier, the barrier exerts a force on the trolley to stop the trolley. We would call this an external force, a force external to the system of the trolley and marble. Since the force acts on the trolley and the marble is not physically attached to the marble, the marble is unaffected by the external force and carries on as before in a straight line. The marble is not thrown forward by the collision; it merely continues with what it was already doing, completely unaware that a force has acted on the trolley. This is why you should wear a seat belt. It demonstrates the property of mass called inertia, as expressed in Newton's First Law. Objects with mass carry on in a straight line with a steady speed unless an external force acts on them.

Cadiar Berwyn and the Roswelsh incident

We climbed Cadair Berwyn which turned out to be a hidden gem. A shapely peak from which we could see most of Wales. Our guidebook mentioned the Roswelsh incident (see https://www.higgypop.com/news/berwyn-mountains-ufo-crash/) Sadly we were not visited by aliens but did love this guide to lights in the sky that appeared on my favourite NASA website yesterday https://apod.nasa.gov/apod/ap170924.html

Free fall at Pistyll Rhaeadr

We went to see the tallest waterfall south of Scotland. It is supposed to be taller than Niagara. Objects feel weight because of the normal contact force (formerly known as the normal reaction force) pushing back up on them. This is when the weight of an object pushing down on a solid compresses the springy electostatic bonds between atoms. When objects fall through the air, this can't happen. There is no normal contact force so there is no reason for an object to "feel" the gravitational pull, even though it is falling. I watched the water falling and made it seemingly freeze by fixing my gaze on a particular piece of falling water. For this piece of water, it would have seemed to exist in a world devoid of gravity until it hit the bottom.

How far away are we from Blackpool?

I was impressed that you could see the Lakeland fells so clearly from Blackpool. I used the usual trick. My little finger is worth 1 degree. The fells subtend half a degree. Half a degree is 8.7 x 10^3 radians. Arc length = radius x angle in radians. The height of the fells is the arc length. The height of the fells is roughly 800m. So distance to the fells is 800/8.7 x 10^3 = 92km. That's far too big!

Centripetal acceleration on the big wheel at Blackpool

I timed the big wheel as it went round. 42 seconds for a complete spin. 2 pi radians in 42 seconds is 0.15 radians per second - the angular velocity. Linear velocity v = radius x angular velocity. I estimate the radius to be 15 metres. So the people are moving at a speed v of 2.2 metres per second along a tangent to the circle. They have an angular acceleration towards the centre which is v squared/r = 0.33 m/s/s.

Blackpool Trams and return current

I was looking at the trams and wondering how the current gets back to the substation. I know that the current flows out along the overhead cables and then down into the trams and into the electric motors. But for there to be a complete circuit, it has to flow back to the substation. The answer is that it flows back through the wheels and the rails. Why doesn't that hurt people? Because it is at very low potential. It is apparently a problem that the current will return via the Earth by going into utility pipes and causing corrosion by electrolysis http://www.tautonline.com/stray-current-myth-or-legend/

Off Blackpool Tower

Blackpool Tower is 158 metres tall. Assuming no air resistance, height = 0.5 x g x t squared which would mean that a stone dropped from the top would take 5.7 seconds to hit the ground. Using v squared = u squared + 2as, the speed with which it hit the ground would be 56 metres per second.

Wave breaking in the wrong direction at Cummersdale

I spotted a wave breaking in the wrong direction at Cummersdale on the River Caldew. The water was flowing away from me but the wave was breaking back in my direction. We think it was going over an old weir. It might have been reflecting off something and thus coming backwards. That is the condition needed to form a stationary wave and the formation was long-lasting although the water was flowing away down the river.

Carlisle's first power station

I'd never noticed the label on this building opposite the swimming baths. It turns out to be Carlisle's first power station from 1899. According to http://www.cumbria-industries.org.uk/a-z-of-industries/electricity/ it had a capacity of 370 kW. According to https://en.wikipedia.org/wiki/List_of_onshore_wind_farms_in_the_United_Kingdom one of the wind turbines at Great Orton (Watchtree) has a nominal capacity of 660 kW and that's for an old wind turbine. There are some land based turbines in Cumbria rated as 2300 kW. No wonder it was for electric lighting. The use of kettles or heaters would have over loaded the system!

Solar roof at the Centre for Alternative Technology

I was impressed that the roof was producing 2.4 kW in the rain but it is supposed to be a 20 kW roof! It has been there almost 11 years, so say 96 000 hours. Halve that to give daylight so say 48 000 hours. Given the number of kWh generated, that means it averages 2 kW.

A gibbon pendulum at Bassenthwaite

We were treated to a fabulous display of gymnastics by this gibbon. I timed the pendulum swings: 25 seconds for 10 swings. The formula for a pendulum is time period T=2pi x sqrt(length/g). This means that the length of the pendulum is 1.5 metres. The big question is to where that is measured. The gibbon is holding on in two places. 1.5 m is further down than the top hand. I suspect that 1.5 m will be down to the centre of mass.

John Dalton's house at Eaglesfield

John Dalton's childhood home at Eaglesfield near Cockermouth is one of the secrets of the Lake District. It is now on the John Dalton Way - a walk that takes you from Cockermouth down to Sellafield where John Dalton's work on atoms has been applied industrially. I was interested to note that he was credited with recognising colour blindness because I saw a programme recently on James Clerk Maxwell which said he'd found out why colour blindness happens. http://www-groups.dcs.st-and.ac.uk/history/Projects/Johnson/Chapters/Ch4_2.html You can see over into Scotland from Eaglesfield, almost to near where Maxwell lived.

Minutes at Chanonry Point

Chanonry Point near Inverness is an amazing place to go to watch dolphins. Hence the large crowd gathered in the bottom photograph. The latitude is given as 57 degrees and 34.44'. The ' stands for "minutes". Each degree is subdivided into 60 smaller divisions called minutes of arc, and indeed each minute can be further subdivided into 60 seconds of arc, meaning that 1 degree is worth 3600 seconds of arc (denoted ''). I've never seen decimal fractions of a minute before, though. That's like mixing metaphors. It suggests that the precision of the measurement is +- 0.01 minutes of arc. A whole circle is 360 degrees or 21600 minutes. So there are 2.16 x 10^6 lots of 0.01 minutes of arc in a whole circle. A whole circle is worth 2 x pi radians so 0.01 minutes of arc is worth 2.9 x 10^-6 radians. Arc length = angle in radians x radial distance. The radius of the Earth is 6400 km. That means that the latitude of the lighthouse is given to a precision of +- 19 metres.

Yes Tor: in the balance

This is the flag pole on top of Yes Tor on the Okehampton Range. It is balanced and designed to be tipped over. I estimate the counterweight on the bottom to be 4 plates of 15 cm x 50 cm x 1 cm = 750 cubic centimetres each. Say steel is 8 grams per cubic centimetre, then each plate has a mass of 6 kg giving a total of 24 kg. I estimate the triangular plate to be 50 cm across the base and 75 cm high. If it is 1 cm thick, it has a volume of 1/2 x 50 x 75 x 1 = 1875 cubic centimetres. That would give a mass of 15 kg. For simplicity, let's stick the total centre of mass at 55cm down from the pivot. The moment = 0.55 x (240N + 150N) = 214 Nm. This must balance the flag pole. Flag pole is about 2.5 metres long so centre of mass half way along at 1.25 m. 214Nm/1.25m = 172 N or 17.2 kg. Say it is a scaffolding pole of thickness 0.5 cm and radius r. Volume of steel = 2 x pi x r x 0.5 x 125 cubic centimetres = 157r cubic centimetres. Mass = 8 x 157r = 1256r grams = 1.256r kg = 17.2 kg so r = 0.07 metres or 7 cm radius. 14 cm diameter seems a bit high but given the estimates it's in the correct ball park.

Making a Cartesian Diver

I made a Cartesian Diver by cutting the tip off a plastic dropper pipette. I then wrapped blu-tack round the open end so that it would float upright. I half filled the remains of the dropper with water and upended it into a bottle of water. What took time to perfect was getting the correct balance between the weight of blu-tack pulling downwards and the upthrust due to the air. Too much blu-tack and it sinks to the bottom and stays there; too much air and it won't go into the water. It took 10 minutes of trial and error with much emptying of the bottle to extract the diver to get it to work. Once complete, the bottle top needs to be tight on. Then squeeze the sides of the bottle and watch it sink...

The explanation is that the increased water pressure squeezes the air molecules closer together. This makes the air more dense. Things float when they are less dense than water. The careful balancing act here ensures that the extra pressure exerted is enough to increase the density enough to cause it to sink.

Scattering due to magnesium oxide

My class were burning magnesium ribbon to make magnesium oxide. Then I turned on the projector. The light beam was clearly visible. The magnesium oxide smoke must have filled the room with tiny particles despite having the windows open. The smoke particles knock light sideways. This is called scattering. The picture shows the light coming sideways towards us despite giving the illusion of being the light that goes straight on.

Measuring acceleration due to gravity

I came up with a complicated way of measuring acceleration due to gravity so that the class would have to use acceleration = change in speed/time taken rather than have the computer do the calculation for them. I used 3 light gates. The computer timed the fall from the top light gate to the bottom light gate and that came out at 0.281 seconds. Another light gate at the bottom was attached to a datalogger that measured the transit time of a 10cm card at the bottom, which was 0.028 seconds. The speed of the card at the bottom was thus 0.10/0.028=3.6 m/s. It reached that speed from standstill in 0.281 seconds. Acceleration = change in speed/time taken = 3.6/0.281= 12.8 m/s/s. True value is 9.81 m/s/s so we were out by 30%. That's a bit high!

Metal detector at Bosworth

The museum at the Bosworth battlefield had this metal detector exhibit. You moved the detector horizontally along the top and noted that it buzzed when you could see a metal object in the tank below it. The detector consists of a coil with alternating current flowing in it. This sets up an oscillating magnetic field. When a metal object cuts this field, an eddy current is induced in the metal object in accordance with Faraday's Law. The eddy current is alternating because the field that creates it is oscillating. The oscillating alternating current in the metal object turns that into an electromagnet too. It produces its own magnetic field. This second magnetic field must always oppose the original magnetic field. If it added to it, energy would have been magicked up out of nowhere. Thus the second field weakens the first. If the metal detector contains a sensor coil for magnetic fields, then it can sense this weakening an trigger an audio alarm.