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Fast and slow

Change and motion · level 1, lesson 2 of 6

A question to start

A snail and a car have a race. The snail crawls all day long, from breakfast to bedtime. The car drives for only one second and then stops. At the end, the snail has gone further than the car!

So is the snail faster than the car? Of course not. But the snail did go further. What went wrong with this race? By the end of this lesson you will know exactly what was unfair, and how to run a race that is fair.

The idea

Moving changes where you are

When something moves, it changes where it is. A moment ago the ball was in your hand; now it is in the air; now it is on the grass. Moving is a kind of change, just like growing. Growing changes how big something is. Moving changes where it is.

Fast and slow

Something is fast when it gets far away from where it started very quickly. Something is slow when it takes a long time to get anywhere.

From slow to fast, here are some movers:

snail rover walking bike car slow fast
  • A garden snail is very slow. In one minute it might crawl about as far as the length of your finger.
  • The rover is a robot car that drives on Mars. It is slower than you walking! It drives slowly on purpose, because there is no one on Mars to fix it if it bumps into a rock.
  • A person walking is faster than the rover.
  • A child on a bike is faster than walking.
  • A car on the road is faster than a bike.

The fair race: same time

Here is how to find out who is faster, fairly.

  1. Everyone starts at the same line.
  2. Everyone starts at the same moment ("Ready, set, go!").
  3. Everyone stops at the same moment (when the whistle blows).
  4. Then look: who went furthest? That one is the fastest.
tortoise child dog start

When the whistle blew, the dog was furthest from the start. So the dog is fastest. The child is in the middle. The tortoise is slowest.

Why "same time" makes it fair

Think about the snail and the car again. The snail had a whole day. The car had one second. The snail was given much more time, so of course it could go further. That is like letting one runner start an hour early.

When everyone has the same time, nobody has extra time to use. Then the only reason one mover gets further is that it moves more ground in each moment. That is exactly what "faster" means.

The other fair race: same distance

There is a second fair way, and you already know it from school sports day.

  1. Everyone starts at the same line at the same moment.
  2. There is a finish line, the same for everyone.
  3. Who gets there first? That one is the fastest.

Here everyone goes the same distance, and the fastest one takes the least time.

Both races are fair, and they always agree. If the dog wins the "same time" race, it will also win the "same distance" race. Why? If the dog is further ahead when the whistle blows, then it is ahead the whole way, so it reaches any finish line before the others.

Faster and slower words

  • faster, slower: "a bike is faster than walking."
  • fastest, slowest: "the dog was the fastest of the three."
  • as fast as, the same speed: two children holding hands and running together go just as fast as each other.
  • speed: how fast something goes. "The car's speed is high. The snail's speed is low."

Things change speed

A mover does not always keep the same speed. A car is slow when it starts, fast on the open road, and slow again when it stops at a red light. A child runs fast at the start of a race and gets tired at the end. You will learn more about speeding up and slowing down in level 2.

Worked examples

Example 1. Toy cars. Three toy cars are pushed from the same line at the same moment. After a count of three, everyone shouts "stop!" and the cars are caught. The red car went 2 floor tiles, the blue car went 5 tiles, the green car went 3 tiles.

  1. Same start, same time. This race is fair.
  2. Who went furthest? The blue car, 5 tiles.
  3. Order from fastest to slowest: blue (5), green (3), red (2).

Example 2. Running to the tree. Sam and Mia run from the gate to the tree. Mia touches the tree first.

  1. Same start, same finish: the same distance. Fair.
  2. Mia took less time.
  3. So Mia is faster.

Example 3. An unfair race. Leo walks around the playground for 10 minutes. Ava runs for 1 minute. Leo went further. Is Leo faster?

  1. The times were not the same: Leo had 10 minutes, Ava had 1 minute.
  2. So the race was not fair, and we cannot say Leo is faster just because he went further.
  3. To make it fair, both should walk or run for the same time, say 1 minute. Then Ava, who is running, would go further.

Example 4. Counting steps. Two friends walk side by side. Each time Ana takes 2 steps, Ben takes 3 steps. They stay side by side the whole time.

  1. They stay side by side, so in the same time they go the same distance.
  2. So they move at the same speed, even though Ben takes more steps. Ben must be taking shorter steps.

Try it

  1. Which is faster: a bird flying or a snail crawling?
  2. In a race, Kai, Lily and Noor start together. When the whistle blows, Kai has run 10 big steps, Lily 14 big steps and Noor 8 big steps. Who is fastest? Who is slowest?
  3. Three children run to the fence. Lily arrives first, then Noor, then Kai. Who is the slowest?
  4. A tortoise walks for a whole hour. A rabbit hops for one minute. The tortoise went further. Can you say the tortoise is faster? Why or why not?
  5. Put in order from slowest to fastest: a car, a person walking, a snail, a bike.
  6. Two toy cars roll from the same line at the same moment. When you clap, car A is 4 tiles from the start and car B is 4 tiles from the start too. What can you say?
  7. Why is it fair to start every runner at the same line?
  8. Grown-up question: a snail crawls about as far as your finger in one minute. About how far would it crawl in two minutes, if it kept the same speed?
Answers
  1. The bird. In the same time it goes much, much further.
  2. Lily went furthest (14 steps), so Lily is fastest. Noor went least far (8 steps), so Noor is slowest. (This assumes their big steps are about the same size.)
  3. Kai, because he took the most time to cover the same distance.
  4. No. The tortoise had 60 times as much time. That is not fair. To compare, give both the same time, for example one minute each. Then the rabbit would go much further.
  5. Snail, person walking, bike, car.
  6. They went the same distance in the same time, so they moved at the same speed (at least on average).
  7. If one runner started ahead, they would have less to run, so getting to the finish first would not show they are faster. Everyone must have the same distance to go.
  8. About two finger lengths: one finger length in the first minute and another in the second minute.

Common mistake

Saying "it went further, so it is faster" when the times were different. Always check: did everyone have the same time? Or did everyone go the same distance? If neither is the same, the race is not fair yet.

Mixing up "first" and "furthest". In a same-distance race, the winner is the one who arrives first (least time). In a same-time race, the winner is the one who goes furthest. Both are the fastest, just measured two ways.

Where it leads