← All lessonsGRADE 8
SCIENCE · A FAIR RAMP TEST

Plan a Fair Ramp Test

A stack of books, a ramp, a toy cart and a tape measure along the floor. Does a steeper ramp send the cart further? Learn to run a test nobody can argue with: change one thing, do three runs, keep every result. Then find out why the cart keeps rolling across the floor when nothing is pushing it.

4 FILMS · ABOUT 30 MIN
01 Warm-up · 60 seconds

What do you remember?

Write two things you remember from last lesson in Science. No peeking: just what's in your head.

1:00
02 Opening question

Make your first call

Your buddy wants to know if a higher ramp sends a toy cart further across the floor. He lets the cart go once from a low ramp. Then he stacks on more books, piles rocks in the cart and gives it a hard shove from the top. It goes way further. He says, “See? Higher ramp, further roll. Proven.”

Did his test really show that the higher ramp made the difference? What would you change about the way he ran it? Make a guess before you watch.

03 Why this matters

Make it fair, then read it

Last lessons you learned how forces change motion and how mass changes what a push does. Today you'll put that to work on a real test: a toy cart let go at the top of a ramp (books under one end), rolling out onto a flat floor. The question: does a steeper ramp make it roll further?

A test only counts if it's a fair test. You change one thing, you measure one thing, and everything else stays the same. Runs never come out exactly the same, so you'll do three at each height and learn which number goes in the table. Then you'll read a real set of results, odd run and all, and find the pattern.

Last of all: once the cart is on the flat floor, nothing pushes it forward. So why does it keep rolling, and what finally stops it?

04 Teaching film 1 · 1 min

A fair test changes one thing

Film 1 of 4Then: try it ↓
Try it

Build a fair plan

The question: does a steeper ramp make the cart roll further? Build the plan one part at a time, the way you'd write it on a card before the first run.

Change only… …
Measure… …
Keep the same… …
At the start mark, the cart is… …
A plan that raises the ramp and adds bricks to the cart gets struck, because… …
05 Checkpoint

Use it right away

True or false? Raise the ramp, same cart: fair test.

New question: does the cart roll further on the kitchen tiles or on the living-room carpet? Write your plan in your own words: what you change, what you measure, and what you keep the same.

06 Teaching film 2 · 2 min

Three runs each, because runs vary

Film 2 of 4Then: try it ↓
Try it

Why three runs?

The cart gets let go from the 20 cm ramp three times. Pick the step that makes both joins true.

  1. Three runs from 20 cm: 118, 125 and 121 cm.
  2. so
  3. ? Which step goes here?
  4. so
  5. One run on its own could be the lucky one.
  6. so
  7. ? Which step goes here?
  8. so
  9. The middle one, 121, goes in the table.
07 Checkpoint

Use it right away

True or false? Runs of 62, 58 and 60 cm: 60 goes in the table.

08 Teaching film 3 · 2 min

Read the table: keep the odd run, find the pattern

Film 3 of 4Then: try it ↓
Try it

Read the table

Here are the trials for all three heights. Guess each step before you tap Next.

  1. Predict: One run doesn't fit the others. Which one?
09 Checkpoint

Use it right away

True or false? The cart rolls the same distance from every height.

Your cousin runs the ramp test. His 20 cm runs come out 119, 122 and 75, because the cart clipped a chair leg on one run. He wants to rub out the 75. What should he do with that run, and which number goes in his table? Explain in your own words.

10 Teaching film 4 · 1 min

Why it rolls on, and why it stops

Film 4 of 4Then: try it ↓
Try it

Off the ramp, onto the floor

The cart has just rolled off the ramp onto the flat floor, moving at 2 m/s. Nobody is pushing it forward now. The floor and the air push back. Answer first, then take the controls.

Predict first: On the flat floor, nothing pushes the cart forward. What will it do?

Live
Net force
Speed
Speed (→ is +)
0last 10 s

Your goal: Without pushing it, make the cart roll on at one steady speed for two seconds.
  • There's no forward arrow on the floor, and the cart still rolls. A moving thing keeps going on its own.
  • There's only a push-back arrow, so the cart slows, then stops.
  • Rough carpet: a bigger push back, so it stops sooner. Slick floor: no push back, nothing slows it, and it rolls on at the same speed.
11 Checkpoint

Use it right away

True or false? On the flat floor, a forward push from the ramp still acts on the cart.

A bike rider coasts down a steep hill road, then rolls along the flat at the bottom without pedalling, slower and slower, until he stops. Say why he sped up on the hill, why he kept rolling on the flat with no pedalling, and what stopped him.

12 Put it to work

Your turn, no help

Short answers: which sled, or which second change spoiled the test.

One of these comes from earlier lessons, mixed in. For each one, decide which idea it needs before you answer.

At ice-fishing camp you kick two matching sleds across the frozen pond, the same kick each time. The orange sled holds only a tackle box. The black one holds a tackle box, a tent and two buckets of minnows. Which sled picks up more speed from your kick?
Jake is testing if a higher ramp makes the cart roll further. He raises the ramp from 10 cm to 20 cm, and he also moves the whole setup from the kitchen tiles to the hall carpet. What else did he change that should have stayed the same?
True or false? Dots a second apart at 0, 4, 8, 12 m, then 12, 12: steady speed all the way.
Two that look alike
  1. At ice-fishing camp you kick two matching sleds across the frozen pond, the same kick each time. The orange sled holds only a tackle box. The black one holds a tackle box, a tent and two buckets of minnows. Which sled picks up more speed from your kick?
  2. True or false? Dots a second apart at 0, 4, 8, 12 m, then 12, 12: steady speed all the way.

You answered both of these in the practice above. They look alike. For each one, write what you did first, and the word or sign in the question that told you to do that.

13 What changed your mind?

Back to your first answer

Your first answer
You haven't saved a first answer yet. Scroll up to the opening question.
The answer
No. He changed three things at once: the height, the load and the shove. The cart did go further, but there's no way to tell which change did it. One run each could also have been a lucky one. Change only the height. Let the cart go from the same mark without pushing it, with the same load, on the same floor, and do three runs at each height.

At the top, your buddy loaded the cart with rocks, shoved it off a higher ramp and called it proven. Plan him a better test now: what to change, what to keep the same, how many runs, and what to do with a run that goes wrong.

14 The lesson to keep

In four lines

15 Keep it with you

Test yourself

Answer in your head first, then tap the card.

16 How this fits God's world

Held steady

Things keep doing what they're doing until something acts on them. The cart needs no push to keep going, only one to stop. “He upholds the universe by the word of his power” (Hebrews 1:3).