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Chapter 9.1

Chapter 9.1. Forces and Buoyancy. Force. An influence that causes an  object  to undergo a change in motion Generally a push or a pull. Balanced forces. These forces cancel each other out Equal in strength Opposite in direction Results in no movement. Unbalanced forces.

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Chapter 9.1

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  1. Chapter 9.1 Forces and Buoyancy

  2. Force • An influence that causes an object to undergo a change in motion • Generally a push or a pull

  3. Balanced forces • These forces cancel each other out • Equal in strength • Opposite in direction • Results in no movement

  4. Unbalanced forces • These forces do not cancel each other out • Unequal in strength • Result in a change of motion for the object • Speed • Direction

  5. Difference between Mass and Weight Mass Weight Measure of push or pull on an object Gravity Measured in Newtons 9.8 N/Kg • The amount of matter an object has • Cells and atoms • Stays the same • Kilograms

  6. Buoyancy • The upward force on objects either floating or submerged in water. • If the object floats it has neutral buoyancy

  7. Archimedes’ principle • The amount of buoyant force exerted on a submerged object equals the weight of the water that has been displaced.

  8. Density and buoyancy • If the density of the object is higher than the fluid then the object will sink! • What if the object does not have one specific density? • Average density needs to be calculated • Total mass divided by total volume

  9. Average Density • Total mass that makes up a substance divided by the total volume • Masstotal/volumetotal

  10. Benefits of average density • Causes large ships to float • Fish have a swim bladder (air bladder) • Mixture of air and water • Air decreases, fish can go lower • Adapted for submarines

  11. Which will Float? • Wooden boat vs. water logged stick. • Metal block vs. metal boat • Sealed empty bottle vs. full water bottle

  12. Pressure • Force acting on a certain area of surface • Larger the force, greater the pressure • Smaller the area, greater the pressure

  13. Calculating Pressure • Unit of pressure is Pascal (Pa) • Can determine pressure if you know force and area

  14. Sample problems • An aquarium is filled with water that weights 10,000 N. If the base of the aquarium has an area of 1.6 m2, what pressure does the water exert on its base? • P = F/A • P = 10,000N/1.6m2 • P = 6250 Pa

  15. Sample Problems • If the atmospheric pressure is 101,200 Pa and you are holding your hand, the atmosphere is exerting a force on your hand. If the area of your palm is 0.006m2, calculate the force on your hand. • F = P x A • F = 101,200 Pa x 0.006 m2 • F = 607N

  16. Atmospheric Pressure • Pressure exerted by the layers of air surrounding the Earth • Reaches roughly 160 km above the Earth

  17. Pascal’s Law • Pressure applied to an enclosed fluid is transmitted with equal force throughout the container • Basics for hydraulic and pneumatic devices

  18. Hydraulics • Study of pressure in liquids • Hydraulic systems transmit applied force through a liquid to move something else • Liquids are incompressible • Must be enclosed in a tube or pipe

  19. Pneumatics • Gas used to exert force on the gas in an enclosed space • Compressors necessary as gases can be compressed. Build up air pressure.

  20. Pressure and Volume • Increasing pressure of a fluid will decrease volume by the same amount • Boyle’s Law

  21. Temperature and Volume • Increasing temperature will increase the volume of a fluid

  22. Temperature and Pressure • Increasing temperature of fluids will increase the pressure.

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