Science 8 – Mechanical Systems: Concept 2 Review Guide

Key Terms and Definitions

1. Efficiency: The measure of how well a machine uses energy.
2. Work: Occurs when a force is applied to an object, and the object moves.
3. Newtons: Units that force is measured in.
4. Mechanical Advantage: Amount by which a machine can multiply a force.
5. Hydraulic Device: A machine that uses liquid under pressure to move a load.
6. Joules: Units that work is measured in.
7. Work Input: Calculated by multiplying input force by input distance.
8. Pressure: Measure of the amount of force applied to a given area.
9. Pascals: Units that pressure is measured in.
10. Friction: Lowers the efficiency of a mechanical device.
11. Pneumatic Device: A machine that uses gas under pressure to move a load.
12. Speed Ratio: How the speed of the object is affected by the machine.
13. Input Distance: The length of a ramp.
14. Force: Weight of an object.

Calculations and Problem Solving

Pulley System (Salih's Example)

• Mechanical Advantage Calculation:
  • Ratio of output force (load) to input force.
  • Formula: ( \text{MA} = \frac{\text{Output Force}}{\text{Input Force}} )
• Speed Ratio Calculation:
  • Ratio of input distance to output distance.
• Efficiency Calculation:
  • ( \text{Efficiency} = \left( \frac{\text{Work Output}}{\text{Work Input}} \right) \times 100%

Machine Use Situations

• Mechanical Advantage > 1: Useful in situations where force needs to be multiplied.
• Mechanical Advantage < 1: Useful when speed or distance is more important than force.

Ramps and Work

• Shallower Ramp Disadvantages:
  1. Increases the distance needed to move the object.
  2. May require more space for setup.
• Work without Movement:
  • Example: Holding a heavy object stationary requires force but does no work.
• Work Calculation:
  • ( \text{Work} = \text{Force} \times \text{Distance} )

Ramp (Katrina's Example)

• Mechanical Advantage: Calculate using force and distance.
• Speed Ratio: Calculate based on length and height of ramp.
• Work Input and Output: Calculating using force and distances.
• Efficiency: Compare work output to input.
• Increasing Efficiency: Reduce friction or adjust the ramp angle.

Hydraulic Jack

• Pressure Calculation:
  • Formula: ( \text{Pressure} = \frac{\text{Force}}{\text{Area}} )
• Effect of Piston Size Change:
  • Decrease Input Piston Size: Increases pressure with the same force.
  • Increase Output Piston Size: Reduces pressure output.