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Homework | Tutorial 25

Date: 2020-08-11
  1. simple writing exercises (aiming for 1-3 paragraphs)
  2. Session 1
    1. Why shouldn’t you look at the sun?
    2. What is swimming?
  3. Session 2
    1. Why do people swim?
    2. Why are there tides?
    3. What are tides?
      1. q: what more to say without just describing them or quirks?
    4. What are shoes for?
  4. comments on session 2
  5. session 3
    1. What are fungi? How are they different than plants? (1+5 min speed thing)

simple writing exercises (aiming for 1-3 paragraphs)


  • practice:
    • beforehand
      • brainstorm relevant things, try to make atomic ideas / basic single chunks (or break down ideas into this)
      • have goal written down (can increase specificity as I write if needed), audience, purpose, pre-existing knowledge, etc
    • when writing
      • do an outline
      • each sentence should have a purpose
        • could analyse some answers after the fact and try and figure out the purpose
        • check each sentence for
          • vagueness
          • how does it help the goal
          • does the audience already know this (if it’s not important to say for other reasons)
          • are there any common questions to pre-address
          • is the sentence consistent with the rest of the paragraph/answer
      • can write the same thing multiple times if stuck
      • don’t fixate on one point; keep flow
    • eval after writing
      • if I’ve avoided some details: when someone learns the truth will they be surprised or feel betrayed; will it seem like a lie?
      • was anything left out that seems important?
      • any inelegancies that need cleaning up?

Session 1

Why shouldn’t you look at the sun?

  • the sun emits LOTS of photons
  • photons have energy
  • photons can cause molecules to change if they’re high energy or there are a lot of them
  • our eyes focus light on to our retinas
  • our eyes are used to normal daylight or below
  • when our eyes focus normal daylight (not look at the sun) on to our retinas it doesn’t do damage because our retinas can cope with it
  • the sun is brighter than normal daylight
  • when our eyes focus direct sunlight on to our retinas it’s like when you use a magnifying glass
  • all that light gets focused on to our retinas and they can burn
  • this isn’t normal for retinas so they can’t heal
  • that means permanent damage

we can see things because, when we look at them, the things reflect light and this light goes into our eyes and lands on the back-side (the retina). Our retinas are made of many tiny sensitive light detectors. These light detectors make signals when light hits them. those signals go to the brain which turns them into the image we see. all of these things need to work correctly for us to see, if anything goes wrong then we won’t see anything.

there are lots of ways things could go wrong so that you don’t see anything, but some are worse than others. one reason you might not see something is if there’s no light: maybe it’s dark or you have your eyes closed. if there’s no light then nothing will land on your retinas and no signals will get sent to your brain (which is why you can’t see when it’s dark or your have your eyes closed). that’s easy to fix because you can just turn on a light or open your eyes. other things can go wrong though, which might be very bad. one way the might go wrong is if your retinas stop producing signals. then it doesn’t matter if your eyes are open or closed, you still won’t see anything because no signals get generated so nothing gets sent to your brain. if your retinas stop working forever then you might not ever see again.

[outline.s] light has energy

focusing light to a point makes a lot of heat in that spot. light is usually spread out, but we can make a lot of light land on one spot using a lens (like the one in a magnifying glass) if we do that, the spot where the light lands gets hot enough to burn things. some people use a magnifying glass and the sun to burn pictures in wood.

our eyes are like little magnifying glasses; they each have a lens to focus light on to our retinas which makes the image. this isn’t a problem normally because our eyes can deal with the amount of light we get when we look at normal things like buildings, trees, books, or other people.

[outline.s] but if something is really bright - like the sun - it can shine a lot of light on our retinas.

[outline.s] retinas can’t heal like cuts and bruises, so damage to them can be permanent. doctors can’t fix retinas very well, so if you damage them they might never heal, which means they won’t work and you won’t see anything anymore.

[outline.s] if we look long enough then it can do things like boil the insides of our eyes which will make you completely blind

(stopping here, it’s long enough, might come back and edit later)

What is swimming?

swimming is using one’s body in coordinated motions to move through the water. lots of animals swim. humans use their arms to pull themselves through the water, and their legs to push. land animals that don’t have arms usually use their front legs to pull and back legs to push. typically, animals that live in the ocean swim using their whole body to push against the water. lots of animals that live in rivers and lakes do this too. these animals often have smooth skin (or scales) and have^1 big tails which makes swimming easier.

there are some exceptions to the normal ways of swimming, though. some land animals, like snakes or alligators, have small legs or no legs at all, so they swim using their whole body like fish and dolphins. some sea creatures, like adult crabs, aren’t very good at swimming so tend to live on the sea floor. some birds can swim, too. penguins are one example; they use their wings both to push themselves through the water and to steer too.

Session 2

Why do people swim?

  • exercise
    • low strain
    • easier than running for ppl with physiological issues
      • easy on legs
      • easier if obese
  • enjoyment
    • team sports
    • competitions
  • survival
    • get back to shore
      • rips can drag ppl out
    • away from predators
    • save someone else
    • hunting for food

People swim for lots of reasons. Some of these reasons people swim are for exercise, enjoyment, or survival. Most cases of swimming are voluntary; the person wants to go swimming.

Some people swim for exercise. Swimming can be a good exercise for certain people because it is less stressful on their body than land-based activities. That could be because they’re obese and swimming is easier for them. Or because they’ve hurt one of their limbs and need to move it regularly but can’t do other exercises – like if they can’t put weight on one leg or have broken an arm so can’t use weights. Some people enjoy swimming for other reasons too, so it’s more efficient to exercise by swimming too.

Some people swim for fun. They might like a particular sport that’s only played in the water, like water polo. Or they might enjoy racing against other people, so they practice and compete regularly. People seem to especially like swimming at the beach, maybe because they find the waves fun or because they can play fight with friends without worrying about concrete sides of a pool.

Sometimes people need to swim to survive; because their life is at risk. They might drown if they don’t, like if their boat has capsized. Or because they need to get back to shore; they could have been dragged out into the ocean by a rip, or maybe someone pushed them in to the water. Although swimming is much safer than it used to be, sometimes people swim to get away from predators that might attack them if they stay where they are.

Some people swim for work, like swimming instructors or people who do niche kinds of fishing.

Why are there tides?

  • differences in forces
    • due to gravity
      • mostly the moon
      • a little bit the sun
  • earth spins
    • so tides roughly “point” at the moon
    • earth rotates underneath
      • explains cycle time

Tides occur because of differences in the forces acting on water in the ocean, which we notice because the Earth spins. Tides are easiest to notice where the ocean meets land, but can sometimes be observed in rivers or lakes if their geography is just right.

The main source of these differences is the Moon, though the Sun contributes a little bit — this is due to their gravity. The Moon’s gravitational force is a bit stronger on the side of the Earth closest to the Moon, a bit weaker in the middle part, and weakest on the furthest side of the Earth. The average force on the ocean is less than that on the Moon-side of Earth, and more than that on the opposite side. This means the oceans bulge out on the sides closest and furthest from the moon relative to the middle bits; there are two high tides. It’s like the ocean is being pulled towards the moon when it’s closer, and pushed away from the moon when it’s farther — though the ‘pushing away’ is just an illusion: that side is just being ‘pulled towards’ less than all the other water (not to mention the Earth itself, too). That’s why high tides happen at the parts of the ocean that are closest or farthest from the Moon.

Tides occur twice a day, though, not once per Moon cycle; why? The Earth spins on an axis roughly perpendicular to the orbital plane of the Moon. As the Earth rotates the parts of Earth which are closest to or farthest from the Moon change. Those changes occur on a ~24 hour cycle, since that’s how long it takes for the Earth to spin once relative to the Moon. We see the tides go up and down on a ~12 hour cycle because we’re watching them from the surface of Earth, so we’re spinning too.

What are tides?

  • Tides
    • regular
    • up-and-down
      • towards and away from?
        • tides aren’t sideways
  • High tide is …
    • need to answer this?

Tides are the regular up and down movement of the ocean due to gravitational effects from sources like the Moon and the Sun combined with the Earth’s spin.

q: what more to say without just describing them or quirks?


  • the dominant cycle time is 12hrs, though other cycles exist with periods of 24hrs, once per orbit of the Moon, and once per year.
  • high tide for a given place is the name for the time when that place is closest too and farthest from the Moon.
  • low tide for that place is half way between high tides, when that place is the average distance from the Moon in that 24hr cycle.

What are shoes for?

  • covering and protecting feet
  • different shoes
    • activities
    • cultures
    • qualities
  • scarcity of resources - need to use materials available

Shoes are for covering and protecting feet. People have different kinds of shoes depending on the activities they do, or the cultures they’re from.

People choose some shoes because they’re particularly good for certain activities, or at certain times of the year. Some examples of shoes that are specialised like this are running shoes or steel-capped boots. Running shoes are built to make running more comfortable and less stressful on runners’ legs and ankles. They still cover and protect runners’ feet, but they have extra features that make them particularly well suited to running like more padding than usual. Steel-capped boots are made to be especially protective, so that if something really heavy is dropped on them the foot inside won’t be crushed when it otherwise might. They can’t protect against all drops, but they’re much better than typical shoes at doing so. Sandals and thongs (flip-flops) are particular kinds of shoes which only cover part of the top and sides of the foot. This makes them very comfortable in hot weather, or particularly easy to clean if they get sandy. These kinds of shoes are for making their respective activities safer, easier, more comfortable, etc.

People choose some shoes because of their culture. One example is ceremonial shoes which are only used for particular rituals or traditions. Another example is shoes that are made for dressing up, like many high heels. These kinds of shoes might not make life easier for the wearer, and even cause them pain or deform the foot over long periods of consistent wear. When people choose these shoes they’re not doing it to make a particular activity easier or safer, like running shoes and steel-cap boots. They’re doing it for social reasons, like impressing other people or adhering to traditional dress.

comment: hmm, feel like I’m in a bit of an example trap here

comments on session 2

I noticed I wasn’t writing down goals. I didn’t think they’d be particularly useful b/c they seem trivial.

session 3

What are fungi? How are they different than plants? (1+5 min speed thing)

planning: 1 min

writing: 5 min

  • soft
  • don’t photosynth
  • spores
  • grow on trees
  • or in ground
  • underground root network multiple heads
  • different branch of life
  • smelly
  • small
  • frequency

fungi are a type of life. fungi are different from plants, even though they both grow in the ground (sometimes, at least). fungi reproduce with spores. they release lots of them all at once. a single spore can grow into a new fungi. like a seed but they’re asexual.

fungi can grow lots of above ground bits (called fruit) at once from a single root system, unlike trees. the fruit can be removed and the fungi can grow new fruit again. some are designed to be removed to spread spores.

fungi are smelly in a different way to trees. fungi smell like dirt and old socks.

fungi produce above ground bits, or fruit, much more frequently than trees which only do it once (their trunk). they can produce fruit many times from a single root system, or many fruits at once.

fungi are very different to trees genetically. they split off from the rest of the tree of life a long time ago, and have their own branch alongside plants and animals. that means do lots of things that plants, animals, and other life like bacteria don’t do.

fungi don’t photosynthesise like trees do. fungi get all their nutrients from the soil - I think.

fungi taste different to plants, too. but like some plants, you can’t eat all fungi. some fungi are very poisonous to humans.

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