# 7.3 Wheels, pulleys, and blocks Science 14 with Mrs. M.

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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 kW  h 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

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