levers and pulleys

• What are the three classes of levers?

  First, second, and third class
• What is the objective of the lesson on levers and pulleys?

  • Understand what a lever is
  • Identify levers in everyday objects
• How do Class 1 levers operate?

  They act in a seesaw or scissor action with the fulcrum between the load and effort
• What is the action of Class 2 levers?

  They act in a wheelbarrow action with the load between the effort and fulcrum
• Describe the action of Class 3 levers.

  They have a pincer-like action with the effort between the load and fulcrum
• What are the three elements at work in a lever?

  • Effort
  • Load
  • Position of the fulcrum
• What is the formula to calculate mechanical advantage (MA)?

  MA = \frac{\text{Load}}{\text{Effort}}
• Calculate the mechanical advantage (MA) if the load is 200N and the effort is 50N.

  MA = \frac{200N}{50N} = 4
• What happens when the effort and load are equal in a mechanism?

  Equilibrium can be created
• If two people of the same weight sit equidistant from the fulcrum of a seesaw, what will happen?

  The seesaw will balance
• Where should a person sit on a seesaw if they have twice the mass of another person?

  They should sit half the distance from the fulcrum
• If person A has a mass of 75kg and is seated 2 metres from the fulcrum, how far should person B sit away if they have a mass of 100kg?

  Person B should sit 1.5M from the fulcrum
• How do pulleys and belts transmit rotary motion?

  • Using friction
  • From a driver shaft to a driven shaft
• What can pulleys control in a system?

  Speed and direction of rotation
• What materials are belts often made from?

  Rubber and other materials
• What is the shape of a V-belt used for?

  To help with efficiency
• What is the formula for calculating the velocity ratio (VR) in a pulley system?

  VR = \frac{\text{Driven pulley diameter}}{\text{Driver pulley diameter}}
• If the driver pulley diameter is 400 and the driven pulley diameter is 200, what is the velocity ratio?

  VR = \frac{400}{200} = 2:1
• How does the size of the driver motor affect the pulley system's operation?

  A larger driver motor would increase the input speed
• How do you calculate the output speed of a driven pulley?

  Output Speed = \frac{\text{Input Speed (RPM)}}{\text{Velocity Ratio}}
• If the input speed is 90 RPM and the velocity ratio is 3, what is the output speed?

  Output speed = \frac{90}{3} = 30 RPM
• What is a block and tackle system used for?

  • To lift heavy weights
  • Combines pulleys to reduce effort needed
• What happens as more pulleys are added to a block and tackle system?

  The load becomes lighter, but more rope needs to be pulled
• How is mechanical advantage calculated in a block and tackle system?

  It is equal to the number of sections of rope pulling up on the object
• If a 10 N load requires 5 N of force to lift, what is the mechanical advantage?

  The mechanical advantage is 2
• In a pulley system with a 300 N load and three pulleys, what weight is needed to pull the load?

  Weight = \frac{300}{3} = 100 N
• How do you calculate the velocity ratio and output speed of a driven pulley?

  1. Calculate the velocity ratio (VR)
  2. Use the formula: Output Speed = \frac{\text{Input Speed (RPM)}}{\text{Velocity Ratio}}
• If the driven pulley diameter is 15 and the driver pulley diameter is 150, what is the velocity ratio?

  VR = \frac{15}{150} = 0.1 \text{ or } 1:10
• If the velocity ratio is 0.1 and the input speed is 300 RPM, what is the output speed?

  Output speed = 300 \div 0.1 = 3000 RPM
• How fast will the lawnmower blade spin if the driven pulley turns at 3000 RPM?

  The lawnmower blade will spin ten times faster than the speed of the motor