7.3 Wheels, pulleys, and blocks

Science 14 with Mrs. M

Pulleys• A pulley is a grooved wheel to support a rope

or cable for a load• Changes direction of effort

Equilibrium

• Opposing forces are balanced• Weight of load = effort of pulling force

Fixed Pulley• Effort force = load force

Movable Pulley• Tied to the load• Moves with the load

Fixed Pulley Movable Pulley

Check Your Understanding

P 144 • #1 What is the difference between a fixed

pulley and a movable pulley?

• #2 How does each type of pulley make work easier?

Wheel and Axle

• An axle is a shaft attached to a round wheel

Would it take more or less effort if the doorknob were smaller?

Wheel and Axle

Screwdriver

• A screwdriver’s handle is large compared to the head of the screw

• Fat handle is wheel• Screw is part of the axle

Wheel and Axle

Wrench

• It is easier to turn the wrench handle in a circle than it is to turn the small nut

Wheel and Axle

Winch

• Roller is the axle• Turning crank is the wheel

Wheel and Axle

Check Your Understanding

• P 144 #4 You find it difficult to put screws into a piece of wood. You cannot turn the screwdriver. Would you be better to change to a fat-handled or thin-handled screwdriver?

• #5 Give three examples of everyday items that use the wheel and axle as a force multiplier.

7.4 Spinning Our Wheels: Energy and Efficiency

• When a machine is used it loses energy through:– Friction– Heat– Poor combustion

Efficiency

• No machine is 100% efficient• Efficiency compares the energy a machine

uses with the work the machine does• Work output is less than work input

Efficiency Around the House

• Leaving doors open, lights on, furnace on high, T.V. on, or all electronic chargers plugged in costs more on your energy bill

• Light bulbs waste heat energy

Kilowatt hours

• kWh• Amount of electricity used when 1000Watts is

used for one hour

• Why might you use fewer kilowatt hours in summer than in winter?

Environmental Concerns• Burning fossil fuels = pollution• Fossil fuels are non-renewable• Environmentalists advocate for higher

efficiency devices to reduce emissions

Energy Conservation and Sustainability

• Reduce energy use – by turning off lights when leaving room– by carpooling

• Use renewable energy sources

Ch 7 Review

• Key Term Definitions or Reviewing Key Terms• 2, 3, 4, 7a, 10, 11a