Mechanical-Technical
"DOST-SEI Mechanical-Technical! Gears, pulleys, forces - ito ang test ng practical engineering sense mo. Para sa future engineers ng bayan! This section evaluates your understanding of how machines work and your ability to apply physics principles to real-world problems."
1. Simple Machines 🔧
Simple machines make work easier by changing the magnitude or direction of force. These are the building blocks of all complex machinery.
| Simple Machine | How It Works | Mechanical Advantage | Examples |
|---|---|---|---|
| Lever | Rigid bar rotating around a fulcrum | MA = effort arm / load arm | Seesaw, crowbar, scissors |
| Pulley | Wheel with rope that changes force direction | MA = number of supporting ropes | Flagpole, crane, well bucket |
| Wheel & Axle | Larger wheel attached to smaller axle | MA = wheel radius / axle radius | Doorknob, steering wheel, screwdriver |
| Inclined Plane | Sloped surface to raise objects | MA = length / height | Ramp, slide, stairs |
| Wedge | Two inclined planes joined together | MA = length / thickness | Knife, axe, nail, chisel |
| Screw | Inclined plane wrapped around cylinder | MA = circumference / pitch | Bolt, jar lid, spiral staircase |
Three Classes of Levers:
Class 1:
Fulcrum in middle
Load—Fulcrum—Effort
Examples: Seesaw, scissors
Class 2:
Load in middle
Fulcrum—Load—Effort
Examples: Wheelbarrow, nutcracker
Class 3:
Effort in middle
Fulcrum—Effort—Load
Examples: Tweezers, fishing rod
2. Gears & Gear Systems ⚙️
Gears transfer motion and force between rotating shafts. Understanding gear relationships is essential for mechanical reasoning.
| Concept | Rule | Formula |
|---|---|---|
| Direction | Meshing gears rotate in OPPOSITE directions | If A turns clockwise, B turns counterclockwise |
| Gear Ratio | Teeth on driven gear ÷ teeth on driving gear | GR = T₂ / T₁ |
| Speed | Smaller gear turns FASTER | n₁ × T₁ = n₂ × T₂ |
| Torque | Larger gear produces MORE torque | Torque ∝ Gear size |
| Idler Gear | Changes direction only, not speed/torque | Odd number of gears = same direction |
💡 Quick Rule:
Small → Large gear: Speed decreases, Torque increases (good for lifting)
Large → Small gear: Speed increases, Torque decreases (good for fans)
3. Pulley Systems 🏗️
Pulleys change force direction and can provide mechanical advantage when combined.
Fixed Pulley:
- Attached to ceiling/support
- Changes force DIRECTION only
- MA = 1 (no force advantage)
- Example: Flagpole
Movable Pulley:
- Moves with the load
- Reduces force needed by HALF
- MA = 2
- Example: Block and tackle
Calculating Pulley MA:
Count the number of rope segments supporting the load!
- 1 rope segment = MA of 1 (fixed pulley)
- 2 rope segments = MA of 2
- 4 rope segments = MA of 4
Force needed = Weight / MA
4. Forces & Equilibrium ⚖️
Understanding how forces balance is crucial for mechanical reasoning problems.
| Concept | Definition | Application |
|---|---|---|
| Equilibrium | Net force = 0, object doesn't move | Balanced seesaw, hanging weights |
| Torque (Moment) | Force × Distance from pivot | Lever problems, rotating objects |
| Center of Gravity | Point where weight is concentrated | Balance point, stability |
| Friction | Force opposing motion between surfaces | Braking, grip, energy loss |
🔄 Moment Balance (Seesaw Rule):
Weight₁ × Distance₁ = Weight₂ × Distance₂
For a balanced lever, clockwise moments = counterclockwise moments
5. Fluid Mechanics & Pressure 💧
Understanding how fluids behave and transmit pressure is essential for hydraulics and pneumatics.
Key Concepts:
- Pressure: Force per unit area (P = F/A)
- Pascal's Law: Pressure transmits equally in all directions
- Hydraulic Press: Small force on small piston = large force on large piston
- Buoyancy: Upward force on submerged objects
Hydraulic Advantage:
F₂/F₁ = A₂/A₁
Larger piston area = larger output force
Examples: Car brakes, hydraulic lifts, bulldozers
6. Electrical Circuits Basics ⚡
Basic electrical concepts often appear in mechanical-technical sections.
| Circuit Type | Current | Voltage | Characteristics |
|---|---|---|---|
| Series | Same everywhere | Splits among components | One path; if one breaks, all stop |
| Parallel | Splits among branches | Same across branches | Multiple paths; others work if one breaks |
Ohm's Law: V = IR
- V = Voltage (Volts)
- I = Current (Amperes)
- R = Resistance (Ohms)
7. Practice Questions 📝
Question 1: Gear Direction
Gear A (20 teeth) turns clockwise and meshes with Gear B (40 teeth). In which direction does Gear B turn, and what is its speed relative to A?
Answer: Gear B turns counterclockwise (opposite to A). Speed = half of A (because B has twice the teeth, it rotates half as fast).
Question 2: Pulley System
A 100 kg weight is lifted using a pulley system with 4 rope segments supporting the load. What force is needed? (g = 10 m/s²)
Solution: Weight = 100 × 10 = 1000 N. MA = 4.
Force = 1000 / 4 = 250 N
Answer: 250 N (or 25 kg-force)
Question 3: Lever Balance
A seesaw has a 30 kg child sitting 2 meters from the fulcrum. Where should a 20 kg child sit to balance?
Solution: 30 × 2 = 20 × d
d = 60 / 20 = 3 meters
Answer: 3 meters from the fulcrum on the opposite side
Question 4: Inclined Plane
A ramp is 6 meters long and 2 meters high. What is the mechanical advantage?
Solution: MA = Length / Height = 6 / 2 = 3
Answer: MA = 3 (you need only 1/3 of the direct lifting force)
Question 5: Hydraulics
A hydraulic press has a small piston of area 10 cm² and large piston of area 100 cm². If 50 N force is applied to the small piston, what force is produced at the large piston?
Solution: F₂/F₁ = A₂/A₁
F₂ = F₁ × (A₂/A₁) = 50 × (100/10) = 50 × 10 = 500 N
Answer: 500 N
Test Your Knowledge! 🧠
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