DOST-SEI Mechanical Reasoning Reviewer: Belts, Chains, Racks & Connected Wheels

TEACHER ABI · DOST-SEI MECHANICAL REASONING

Belts, Chains, Racks & Connected Wheels

Trace how motion passes from one rotating part to another. Learn direction, relative speed, no-slip relationships, and rack-and-pinion motion from clear mechanism diagrams.

5–10 minute lesson27 original questionsMechanism-first diagramsSaves progress

LessonShortcutExamplesSkill CheckPracticeMasteryFAQ

Your reviewer status

Start with the five-form Skill Check. Your result will guide you to the right practice level.

QUICK REVIEW

Follow the moving contact

1. Open belt
Two pulleys connected by an uncrossed belt rotate in the same direction.

2. Crossed belt
Crossing the belt reverses the driven pulley's direction.

3. Chain drive
A normal chain loop makes the sprockets rotate in the same direction. Tooth count controls speed ratio.

4. No slipping
The belt, chain, rack, or touching rim has the same linear speed at each contact.

5. Smaller radius = faster rotation
For the same rim speed, a smaller wheel or pulley makes more revolutions.

6. Rack-and-pinion
Use the motion of the exact contact point. A gear above a right-moving rack turns counterclockwise.

DO IT FAST

TRACE → CONTACT → COMPARE

TRACE: identify what connects the parts. CONTACT: make touching surfaces move together without slipping. COMPARE: only then use radius, diameter, or tooth count to decide which part rotates faster.

Fast equations: belt/touching wheels: r₁n₁ = r₂n₂. Chain sprockets: T₁n₁ = T₂n₂.

WORKED EXAMPLES

See the transmission before doing arithmetic

1. Open belt

A clockwise driver makes the driven pulley turn clockwise.

2. Crossed belt

Crossing the belt reverses direction.

3. Different pulley sizes

The same belt speed passes both rims. The smaller pulley rotates faster.

4. Rack and pinion

A right-moving rack below a gear makes the gear turn counterclockwise.

5. Touching wheels

External rim contact reverses direction. The smaller wheel rotates faster.

Common traps

Treating every connection like gears: open belts and normal chains preserve direction, while touching wheels reverse it. Ignoring a crossed belt: crossing changes direction. Assuming equal rim speed means equal rpm: it does not. Mixing radius and diameter: use the same size measure on both sides. Guessing rack direction: inspect the exact contact point.

FIVE-FORM SKILL CHECK

Can you transfer motion across five forms?

This diagnoses your next practice step; it does not verify mastery.

CHOOSE YOUR PRACTICE

Practice at the level you need

FRESH MASTERY CHECK

Verify the competency

Mastery requires 5/5. If you miss an item, the next attempt loads a different set.

FAQ

Quick clarifications

Does an open belt reverse direction?
No. Open belt: same direction. Crossed belt: opposite direction.

Why does the smaller pulley rotate faster?
With no slipping, both rims have the same linear speed. A smaller circumference must make more revolutions in the same time.

Are chains solved like belts?
For direction, a normal chain loop preserves direction. For speed, sprocket tooth counts give the ratio.

How do I solve a rack quickly?
Look at the gear's contact point and make that point move in the same direction as the rack.

RELATED COMPETENCIES

Continue Mechanical Reasoning

Gears & Gear Trains · Levers, Torque & Balance · Pulleys & Mechanical Advantage · Wheels, Axles & Rotational Systems · Forces, Friction & Equilibrium

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