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Sc7: Unit 1 Friction lesson 4: Gravity lesson 5: Pressure

Sc7: Unit 1 Friction lesson 4: Gravity lesson 5: Pressure. Unit 1.4: VOC # 4 1. friction 2. sliding friction 3. rolling friction 4. fluid friction 5. lubricants. Unit 1.5: VOC # 6 1. pressure 3. pascal 4. atmospheric pressure

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Sc7: Unit 1 Friction lesson 4: Gravity lesson 5: Pressure

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  1. Sc7: Unit 1 Friction lesson 4: Gravity lesson 5: Pressure Unit 1.4: VOC #4 1. friction 2. sliding friction 3. rolling friction4. fluid friction5. lubricants Unit 1.5: VOC #6 1. pressure 3. pascal 4. atmospheric pressure 5. kilopascal 6. fluids 7. buoyant force 8. Archimedes’ principle 9. density Unit 1.4: VOC #5 1. gravity2. weight3. free fall4. orbits

  2. FRICTION: THE FORCE WHICH OPPOSES MOTION • THREE FACTORS WHICH DETERMINE FORCE OF FRICTION • MASS OR "PRESSURE" OF SURFACES MOVING • TEXTURE OF MOVING SURFACES • LARGER SURFACE AREAS PRODUCE MORE FRICTION • FRICTION OFTEN RESPONSIBLE FOR MOTION AND CONTROLLING MOTION 1.

  3. THE THREE TYPES OF FRICTION • 1. SLIDING FRICTION: SURFACES MOVING OVER EACH OTHER • USUALLY REQUIRES THE MOST FORCE TO OVERCOME • DEPENDS ON OBJECT’S MASS, SURFACE AREA, TEXTURE • 2. ROLLING FRICTION: CAUSED BY ROLLING OBJECTS • REQUIRES LESS FORCE TO OVERCOME THAN SLIDING • CHANGE SLIDING TO ROLLING FRICTION BY USING WHEELS, BALL BEARINGS • 3. FLUID FRICTION: MOVING THROUGH FLUIDS • REQUIRES THE LEASTAMOUNT OF FORCE TO OVERCOME • CHANGE SLIDING TO FLUID FRICTION BY USING LUBRICANTS (OILS, etc.) 2 2

  4. GRAVITY: THE FORCE OF ATTRACTION BETWEEN OBJECTS GRAVITY IS AN “ATTRACTIVE FORCE” : IT ALWAYS “PULLS” AMOUNT OF GRAVITY DEPENDS ON THE AMOUNT OF MASS AND DISTANCEGREATER MASSES, GREATER GRAVITY CLOSER DISTANCES, GREATER GRAVITY WEIGHT: A MEASURE OF THE PULL OF GRAVITY  WEIGHT IS A FORCE MEASURED IN NEWTONS EQUATION: WEIGHT = mg GRAVITY’S ACCELERATION ON EARTH EQUAL TO "9.8m/s2 x kg"  MASS IS NOT THE SAME AS WEIGHT THE AMOUNT OF MATTER  MEASURED IN kg 3

  5. ORBITAL MOTION: A BALANCE OF GRAVITY, INERTIA • PULL OF GRAVITY MUST BALANCE INERTIA • FREE FALL: ONLY FORCE ON AN OBJECT IS GRAVITY • FORCES SATELLITE INTO CIRCULAR MOTION • ORBIT: SATELLITE'S FALL EXACTLY MATCHES EARTH'S CURVE • ORBITAL SPEED IS ABOUT 7,900 m/s • INCREASING SPEEDS CAUSE HIGHER ORBITS • DECREASING SPEED WOULD CAUSE IT TO FALL OUT OF ORBIT 4

  6. PRESSURE: THE DISTRIBUTION OF FORCE • THE FORCE EXERTED OVER AN AREA • SAME FORCE OVER LARGER AREA DECREASES PRESSURE • PRINCIPLE APPLIES TO SHARP KNIVES, SNOW SHOES • EQUATION FOR PRESSURE: P = FORCE / AREA • MEASURED IN PASCALS(Pa): 1 N/m2 = 1 Pa • FORCE MEASURED IN NEWTONS • SURFACE AREA: A FLAT SURFACE (2 DIMENSIONS) • MEASURED IN SQUARE METERS (m2) • AREA OF REGULAR SURFACE: a = l * w • SMALLER AREAS MEASURED IN SQUARE CM (cm2) 5

  7. FLUID PRESSURE: CAUSED BY ALL FORCES OF FLUID’S MOLECULES • FLUIDS: CHANGE SHAPE AND FLOW EASILY; ARE GASES OR LIQUIDS • FLUID PRESSURE IS EQUAL IN ALL DIRECTIONS WITHIN THE FLUID • ATMOSPHERIC PRESSURE: EXERTED BY THE MASS OF THE AIR • ATMOSPHERE OVER 100 km HIGH • AVERAGE AIR PRESSURE: 1013 N/m2 OR 1013 MILLIBARS (mb) • BALANCED PRESSURE: NET PRESSURE IS ZERO • PRESSURE WITHIN AN OBJECT EQUALS THAT OUTSIDE IT • CELLS’ INTERNAL FLUIDS BALANCE EXTERNAL PRESSURE • PRESSURE DECREASES AS ELEVATION INCREASES • PRESSURE INCREASES AS DEPTH INCREASES 6

  8. ARCHIMEDES’ PRINCIPLE: DESCRIBES THE BUOYANCY OF OBJECTS • BUOYANT FORCE IS EQUAL TO THE WEIGHT OF FLUID DISPLACED • WEIGHT OF FLUID DEPENDS ON ITS DENSITY& VOLUME • DISPLACEMENT: VOLUME OF FLUID REPLACED BY OBJECT • VOLUME: AMOUNT OF SPACE TAKEN UP (3 DIMENSIONS) • METRIC UNITS: CUBIC METERS- m3, CUBIC cm-cm3 , cc • BUOYANT FORCE: ACTS UPWARD AGAINST GRAVITY • FLOATING AND SINKING OF OBJECTS • FLOATS IF DISPLACED WEIGHT IS MORE THAN OBJECT’S WEIGHT • SINKS IF DISPLACED WEIGHT IS LESS THAN OBJECT’S WEIGHT • STAYS IN PLACE IF DISPLACED WEIGHT EQUALS OBJECT’S WEIGHT 7

  9. DENSITY: AMOUNT OF MASS PER UNIT OF VOLUME • EQUATION: MASS / VOLUME • VOLUME: HOW MUCH SPACE IS TAKEN UP • OBJECT SINKS IF ITS DENSITY IS GREATER THAN FLUID’S • OBJECT FLOATS IF DENSITY IS LESS THAN FLUID’S • OBJECT STAY IN PLACE IF ITS DENSITY IS IDENTICAL • LARGER OBJECTS WITH SAME WEIGHT ARE MORE BUOYANT • DENSITIES DEPEND ON AN OBJECT’S CHEMICAL COMPOSITION • SOLIDS: WOOD - 0.7 g/cm3 , COPPER – 8.8 g/cm3 • FLUIDS: AIR – 0.00118 g/cm3, WATER – 1.0 g/cm3 8

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