Pulleys and mechanical control systems

Term 2

Key Concepts:

• A single wheel fixed pulley has no mechanical advantage.

• Mechanical advantage is obtained with a single wheel moveable pulley.

• A block and tackle can provide greater mechanical advantage.

• A rachet and pawl is a device that controls turning and movement in one direction.

• A cleat is a device that tightens or holds rope so that it does not form knots.

• A single wheel fixed pulley has no mechanical advantage.

Newton Spring Scale

Mechanical Advantage (MA)

Mechanical Advantage= MA

Load force = LF

Effort force = EF

MA=𝐿𝐹

𝐸𝐹

Mechanical Advantage(MA)

Mechanical Advantage = MA

Load force = LF

Effort force = EF

MA =𝐿𝐹

𝐸𝐹

MA =10𝑁

5𝑁

MA = 2

Force Ratio = 2:1

Mechanical Advantage (MA)

• A = Single wheel fixed pulley

Generates no mechanical advantage.

Only changes the direction.

• B = Single wheel moveable pulley.

Generates mechanical advantage.

• C = Pulley block system.

Generates mechanical advantage.

A B C

Ratchet and Pawlhttps://www.youtube.com/watch?v=7UWYEnmqU68&t=2s

• The rachet and pawl is a mechanical control system that consists of agear wheel with teeth pointing in a sloping direction. The long part has agentle slope, while the short part has a steep slope.

• The pawl is a lever that can be pulled into the teeth with a spring. Thepawl lever could also drop down into the ratchet teeth through gravityas the ratchet turns in one direction.

• The ratchet and pawl allows motion in one direction while the pawllocks to prevent movement in the other direction.

• Examples: Ratchet wrench, Ratchet strap, Turnstile, Ratchet screwdriver

Ratchet and Pawl

BrakesHydraulic brakes

BrakesDisc brakes: Rim brakes: Drum brakes:

Disc brakes operate in asimilar way to the discbrakes of a car. The disc isattached to the hub of thewheel.

Rim brakes work with asystem of levers and brakepads on the rim of thewheel.

Drum brakes are located inthe hub of the back wheeland are operated whenbackward pressure is appliedon the pedals.

Cleats

• A cleat is a device used to secure a rope.

Boat cleat

Hook cleat

Cam cleat

Summary: