Claw Game Maker: Squeeze or Cradle?
A stronger grip is not always a better one. Students bench a capsule ball and find it holds at a grip far below what friction allows, because the curled tips close under it and carry it on their shape. They straighten the tips and it slips; they hook the pads and the bear is cradled at a grip that would never squeeze it. By the end they can say when a claw squeezes and when it cradles, and what each needs.
At a glance
Essential question
When does a claw hold a prize by squeezing, and when by cradling, and what does each need?
Objectives
Students will be able to:
- tell squeezing (friction from the push) from cradling (the tips under the prize, carrying it on their shape)
- show on the bench that a round prize cradles at a grip far below its friction line
- change the tip curl and the pad angle and say what each did to the grab
- explain why a stronger grip can pop a round prize out instead of holding it
Vocabulary
Squeeze, Cradle, Tip curl, Pad angle, Friction line
Standards
MS-PS2-2
Time and materials
45 minutes, grades 6-8.
- One computer or Chromebook per student
- A projector
- The worksheet and exit ticket, one copy each per student
- The rubric, one copy per student if you grade the work
Prep
Make copies of the worksheet and exit ticket. Before class, open mytekdev.com/try/clawmaker?lesson=squeeze-or-cradle&ref=tpt-clawmaker-2 once on a student computer: open Test, bench the capsule ball at 0.3 N and watch it hold, then open Build, Claw and drag Tip curl to nearly straight and bench it again. About five minutes.
Assessment
- Formative: the questions under What to look for, asked while students work, and the exit ticket (answer key included).
- Summative: the worksheet, scored with the rubric.
Technology and privacy
Runs in any browser with WebGL, Chromebooks included, with nothing to install. Students need no account and no email: the link works signed out, and nothing they do is stored on our server unless they choose to save.
mytekdev.com/try/clawmaker?lesson=squeeze-or-cradle&ref=tpt-clawmaker-2mytekdev.com/tools/claw-game-maker/lessons/squeeze-or-cradle/startEach student gets their own copy, and the same link reopens it next time. How to set up a classLesson sequence
| Minutes | Stage | What you do | What students do |
|---|---|---|---|
| 0 to 5 | Warm-up Hook | Show the title, essential question and Today I can slides (about 1 minute). Then the warm-up: more grip or less for the ball? Take a vote and keep the numbers. | Answer the warm-up on the worksheet. |
| 5 to 12 | Direct instruction (I do) Model it | Project the app. Open Build, Claw and zoom in on the claw. Show Three claws and Curled and hooked: drag Tip curl and Pad angle slowly and watch the prongs change as you drag. Say the two words: squeeze and cradle. It's working when: Cup a ball in your fingers from below, then try to lift it by squeezing its sides with straight fingers. | Fill in the vocabulary. |
| 12 to 22 | Guided practice (We do) The ball together | Students open the link. The guide takes them to the bench with the capsule ball at 0.3 N (it holds), then to Build to straighten the tips, back to the bench (it slips), then to hook the pads. Walk the room and ask what changed. Watch for: Students who turn the grip up to fix a slip. Ask them to keep the grip and change the shape. | Follow the guide and record held or slipped each time. |
| 22 to 38 | Independent practice (You do) The settings table | Students fill a table: for the bear and the ball, at straight, curled and hooked tips, the lowest grip that holds. Then bare metal tips with hooked pads: cradling needs little friction, so the bear still holds. If they ask: "The ball slipped at 12 N with straight tips. It held at 0.3 N with curled ones. Why did more grip not help?" Popping out | Fill in the settings table and answer the two questions. |
| 38 to 45 | Closure Showcase and exit ticket | Show the Showcase slide. Go back to the warm-up vote: the ball needed less grip, but not because it is lighter. Hand out the exit ticket. | Answer the exit ticket. |
Before you teach: a ten-minute walkthrough
Open mytekdev.com/try/clawmaker?lesson=squeeze-or-cradle&ref=tpt-clawmaker-2. A claw machine in a room, seen the way a player sees it: a 70 cm box, three rubber-padded prongs parked closed over the chute, and a pile of bears, ducks and capsule balls.
- The ball. Open Test, pick Ball in a capsule on the bench, set 0.3 N and run it. It holds: the curled tips close under it.
- Straight. Open Build, Claw, and drag Tip curl to nearly straight. The prongs change as you drag. Bench the ball at 0.3 N: it slips. At 12 N it still slips: the squeeze pops it out.
- Hooked. Put the curl back and drag Pad angle to hooked. Bench the bear at 0.5 N: cradled.
- Metal. Pick bare metal tips and bench the bear again at 0.5 N with the hooked pads: it still holds. At 0.5 N with straight metal tips it slips at once.
Background for the teacher
A claw can hold two ways. Squeezing uses friction: the tips push in, and friction up along the tips carries the weight, up to a limit set by the push and the grippiness of the pair of surfaces. Cradling uses shape: the tips close under the prize and carry it the way cupped fingers carry a ball, and the push barely matters.
A 45 g capsule ball has a friction line of about 0.3 N with rubber tips, and it cradles at 0.3 N with curled tips. With straight tips it cannot be held at any grip: a hard sideways squeeze on a smooth ball pushes it out, like a wet bar of soap. A bear has limbs the tips can hook under, so hooked pads cradle it at 0.4 N on the bench, half its friction line.
Real arcade claws have curled tips with rubber pads: the curl for cradling, the pads for friction when it has to squeeze. Students who set the pads to hooked find the honest machine check of Build a Fair Machine easier to pass, and the bench shows why.
What to look for
Ask these while students work. A student who has understood the lesson can answer them without help:
- What did the tips do under the ball at 0.3 N?
- Why did the ball slip at 12 N with straight tips?
- Why does the bear cradle with hooked pads even on bare metal?
- Which prize would hooked pads not help, and why?
- What do real claws have both the curl and the rubber for?
Cross-curricular extensions
- Math: the friction line is weight divided by the prongs times the grippiness. Work it out for the ball, the bear and the boxed toy.
- Biology: how do a bird's feet hold a branch while it sleeps? Squeeze or cradle?
- Engineering: sketch a claw for a flat boxed toy, which nothing can get under.
- English: explain cradling to a younger student in three sentences, with a drawing.
Vocabulary
| Squeeze | Holding by friction: the tips push in from the sides and friction holds the prize up. |
| Cradle | Holding by shape: the tips close under the prize and carry it, with almost no squeeze needed. |
| Tip curl | How far the end of each prong bends inward. Straight tips squeeze; curled tips get under. |
| Pad angle | How far the pad at the very end of the tip bends in again, like a fingertip. |
| Friction line | The grip a straight squeeze would need to hold a prize: its weight divided by the prongs and the grippiness. |
Differentiation
English learners
- Keep the vocabulary slide up and act out squeeze and cradle with your hands as you say them.
- Pair each learner with a partner; the table is held or slipped.
- Accept the explanation as two drawings: fingers squeezing a ball and fingers cupping it.
Students with IEPs or 504 plans
- Pair students, one changing settings and one recording.
- Zoom the browser to 150%.
- Allow the ball only in the settings table where the IEP allows a modified assignment.
Students who need more support
- A sentence starter: "The ball held at a tiny grip because the tips ___."
- Fill in the ball's first row together.
- Use the Kid level: the grips read weak, medium and strong.
Students ready for more
- Work out the ball's friction line and compare it with the grip that cradled it.
- Find a pad angle at which the bear holds at 0.5 N, then explain why hooked pads fail on the boxed toy.
- Solve the Slippery ball puzzle under Puzzles.
Adapting for other grades
Younger students: In grades 4 and 5, set the level to Kid, do the guide and the ball's rows only; drop the third rubric row; total 8, and 6 meets the objectives.
Older students: In high school, switch the level to High school and compare each holding grip with the friction line the bench shows: cradling holds under the line, squeezing cannot.
Claw Game Maker: Squeeze or Cradle?
Student worksheet
Name: ______________________________ Date: ______________
Open the app: scan the QR code, or go to mytekdev.com/try/clawmaker?lesson=squeeze-or-cradle
Essential question: When does a claw hold a prize by squeezing, and when by cradling, and what does each need?
Warm-up: A smooth 45 g ball: more grip or less than a 180 g bear? Why? ________________________
- Vocabulary. Squeeze, cradle, tip curl, pad angle, friction line: write each in your own words.
- The guide. The ball at 0.3 N with curled tips: ______. With straight tips: ______. The bear at 0.5 N with hooked pads: ______.
- The settings table. For the bear and the ball, at straight, curled and hooked tips: the lowest grip that holds.
- Bare metal. The bear at 0.5 N, hooked pads, bare metal tips: ______. Straight metal tips: ______.
1. Why did the ball hold at 0.3 N and slip at 12 N?
2. Why do real claws have curled tips and rubber pads?
Claw Game Maker: Squeeze or Cradle?
Exit ticket
Name: ______________________________
1. Cradling a prize means (A) squeezing it harder (B) the tips close under it and carry it on their shape (C) lifting it faster
2. A smooth ball with straight tips (A) holds at a high grip (B) pops out when squeezed hard (C) holds at any grip
3. Hooked pads on bare metal tips still cradle the bear. What does that show?
Answer key: exit ticket
| Question | Answer | Why |
|---|---|---|
| 1 | B | Shape does the holding; the push barely matters. |
| 2 | B | A hard sideways squeeze on a smooth round prize pushes it out. |
| 3 | Cradling needs the shape, not the friction | Squeezing needs grippy surfaces; cradling carries the prize from below. A full answer says friction still helps when it must squeeze. |
Rubric
Score each row from 1 to 4.
Name: ______________________________
| Criteria | 4 Exceeds | 3 Meets | 2 Approaching | 1 Beginning |
|---|---|---|---|---|
| Data | A settings table with the bear and the ball at three tip shapes, the lowest holding grip found for each, and the bare-metal row. | The table with the lowest holding grips found. | A partial table. | No table. |
| Evidence | Uses the bench to show the ball cradling under its friction line and slipping at a high grip with straight tips. | Shows the ball holding at a low grip with curled tips. | Says the ball held, without the comparison. | No evidence. |
| Explanation | Explains squeeze against cradle, what each needs, and why a stronger grip pops a round prize out. | Explains squeeze against cradle. | Says curled tips hold better. | No explanation. |
Total: ____ / 12. A score of 9 or more meets the objectives.
Standards
The lesson is built for MS-PS2-2, with shape as the variable alongside the force.
| Framework | Code | Grades | Standard | How the lesson meets it |
|---|---|---|---|---|
| NGSS | MS-PS2-2 | 6-8 | Plan an investigation to provide evidence that the change in an object's motion depends on the sum of the forces on the object and the mass of the object. | Students change the shape of the tips and the grip one at a time on the bench and record whether the prize held. |
Checked November 2026 against: NGSS MS-PS2-2, Motion and Stability: Forces and Interactions.
Optional: save student work in a free class
The whole lesson runs at the link on the worksheet, with no accounts and no sign-up.
To keep students' work, and see it all in one place, make a free class. It takes about ten minutes, once, and covers every lesson in this series: mytekdev.com/tools/class-setup
Students in a class open mytekdev.com/tools/claw-game-maker/lessons/squeeze-or-cradle/start instead of the worksheet link. Each one gets their own copy of the starter, and the same link reopens it next time.