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Bigger and smaller over time

Change and motion · level 1, lesson 1 of 6

A question to start

Somebody took three photos of a bean plant, but the photos got mixed up. Can you put them back in order, from the first photo to the last one?

A B C

Most people get this right very quickly: C, then A, then B. A plant starts as a seed, grows a little, then grows a lot. But how did you know? Nobody told you which photo was taken first. You used an idea that is so useful that we will spend the whole lesson on it: some things only grow one way.

The idea

Change over time

Things change over time. That means that if you look at something now, and then look at it again later, it may not be the same. The word time here just means "now, a bit later, and later still", like the ticking of a clock or the days on a calendar.

Here are some things that get bigger over time:

  • a baby, who becomes a child, and then a grown-up;
  • a puppy, who becomes a dog;
  • a bean plant, from a seed to a tall green plant;
  • a pile of leaves you are raking up;
  • the pile of books you have read this year.

And here are some things that get smaller over time:

  • a candle that is burning;
  • a pencil that you keep sharpening;
  • a snowman on a sunny day;
  • a bar of soap that you use every day.

Clues that tell you the order

When you put pictures in order from first to last, you are being a time detective. A detective looks for clues. Here are the best clues for change.

Clue 1: some things only get bigger. A puppy does not turn back into a smaller puppy. A seed that has sprouted does not go back into a seed. So for a growing thing, the smallest picture comes first and the biggest picture comes last.

Clue 2: some things only get smaller. A burning candle never grows back. So for a shrinking thing, the biggest picture comes first and the smallest comes last. This is the same clue turned around.

first last

Clue 3: other things change too, not only size. A baby's hair grows longer. A banana turns from green to yellow to brown with spots. A leaf turns from green to orange and falls off the tree. These changes also only go one way, so they are clues too.

Why the clues work

Why can you be so sure that a puppy picture with a small puppy came first? Because a puppy grows a tiny bit every day. If it was small in one photo and big in another, then all the days of growing must have happened between the two photos. The small photo had to be taken before those days, and the big photo after them.

A grown-up would say the puppy's size is a record of time: the bigger it is, the more time has gone by. That is why a doctor can look at a child's bones and tell roughly how old the child is, and why the rings inside a tree trunk tell how many years the tree has been growing (one new ring each year).

When the clue does not work

Be careful. "Bigger means later" only works for something that only grows. Some things go up and down:

  • A balloon can be blown up, then let down, then blown up again.
  • A puddle can grow when it rains and shrink when the sun comes out, and then grow again in the next rain.
  • The water in a glass goes down when you drink it, and up when you fill it again.

If you see two pictures of a puddle, a big one and a small one, you cannot be sure which came first. It might have dried up, or it might have rained. A good detective says: "I need another clue." Maybe the ground around it is wet in one picture and dry in the other, or maybe one picture shows rain.

First, next, last

When you tell the story of a change, use order words:

  • first (at the start),
  • next or then (in the middle),
  • last or at the end.

For the bean plant: "First there was only a seed in the soil. Then a small shoot came up with two leaves. At the end it was a tall plant with lots of leaves."

Telling the story in order is the same as putting the pictures in order. Both are ways of saying what happened, and when.

Worked examples

Example 1. Growing up. Three photos show the same girl: in one she is a baby in a pram, in one she is riding a bike, and in one she is a grown-up driving a car. Put them in order.

  1. A person only grows up, never down. So this change goes one way.
  2. The baby is the youngest, so that photo comes first.
  3. Riding a bike comes next: she is a child.
  4. Driving a car comes last: she is a grown-up.

Order: baby, bike, car.

Example 2. A shrinking snowman. Three pictures of a snowman: one tall with a hat and a scarf, one shorter and leaning, one just a small lump of snow with the hat lying on top. The sun is out in all three.

  1. On a sunny day snow melts, so the snowman only gets smaller.
  2. The biggest snowman comes first.
  3. The leaning one comes next.
  4. The lump with the hat on top comes last.

Order: tall, leaning, lump. The hat did not change at all. Only the snow did.

Example 3. Two pictures of a balloon. One picture shows a big round balloon, the other a small balloon. Which came first?

  1. A balloon can get bigger (you blow it up) or smaller (air leaks out).
  2. So size alone is not enough. We need another clue.
  3. Suppose in the small picture the balloon is wrinkly and lying on the floor. Wrinkles appear when a balloon has been blown up and then lost air. So that one is probably later.

The answer is "big first, then small", but only because of the wrinkle clue.

Example 4. A banana. Three pictures: a yellow banana, a green banana, a brown banana with spots. Order?

  1. A banana ripens one way: green, then yellow, then brown.
  2. Order: green, yellow, brown.

Here the clue is colour, not size. The banana stays about the same size the whole time.

Try it

  1. Put in order from first to last: a big apple tree, an apple seed, a small tree as tall as you.
  2. Put in order: a long new pencil, a very short pencil, a pencil half as long.
  3. A cat in three photos: a tiny kitten, a big cat, a middle-sized cat. Which photo is last?
  4. Name two things in your home that get smaller over time.
  5. A cup of juice is full in one picture and half full in another. Can you be sure which came first? What clue would help?
  6. A boy builds a tower of blocks. Picture A has 3 blocks, picture B has 7 blocks, picture C has 5 blocks. If he only ever adds blocks, what is the order?
  7. Tell the story of a melting ice lolly using "first", "then" and "at the end".
  8. Grown-up question: why can the rings inside a tree trunk tell you how old the tree is?
Answers
  1. Seed, small tree, big tree. A tree only grows, so the smallest comes first.
  2. Long, half, very short. A pencil gets shorter each time you sharpen it, and it never grows back.
  3. The big cat. A kitten grows into a cat, so the biggest picture comes last.
  4. Many answers, for example: soap, toothpaste in the tube, a candle, a crayon, a roll of toilet paper, the cereal in the box.
  5. No, not just from these pictures. Someone could have drunk half (full first), or someone could be filling the cup (half first). A clue might be a jug pouring in one picture, or a child drinking with a straw.
  6. If he only adds blocks, the number only grows: A (3), C (5), B (7).
  7. For example: "First the ice lolly was whole and cold. Then it started to drip and got smaller. At the end there was only the stick and a puddle of juice."
  8. A tree grows one new ring each year, and the old rings stay inside. So the number of rings is a record of how many years it has grown. Counting rings is counting years.

Common mistake

Thinking "bigger" always means "later". That is only true for things that only grow, like children, trees and puppies. Things that can go up and down, like balloons, puddles and the juice in a cup, need another clue.

Forgetting the things that did not change. When a snowman melts, the hat stays the same. Noticing what did not change is just as clever as noticing what did. You will practise this in lesson 3.

Where it leads