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Motion, Forces, & Machines

Motion, Forces, & Machines. Describing Motion. Motion : the state in which one object’s distance from another is changing . Are You Moving? Reference Point : place or object used for comparison to determine if something’s in motion Good Stationary RPs: Trees , Signs, Buildings

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Motion, Forces, & Machines

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  1. Motion, Forces, & Machines

  2. Describing Motion • Motion: the state in which one object’s distance from another is changing. • Are You Moving? • Reference Point: place or object used for comparison to determine if something’s in motion • Good Stationary RPs: Trees, Signs, Buildings • The Backwards Moving Bus • An Object Is In Motion If It Changes Position Relative To A Reference Point

  3. Relative Motion • Wait… Are you sure you aren’t moving? • Movement Depends on your Reference Point • Chair- NO SUN- YES • We are actually moving at 30 k/sec

  4. System of Measurement • Really Important Experiment…. but different units • It’s important scientists can communicate together • They must have a “universal language” • Metric System- International System of Units or S.I • Base 10 • Length (meter) • 1 meter = 39.4 inchesor .91 yards • Centimeters (cm) are used to measures distances less than 1 meter • 100 centimeters in 1 meter

  5. Easy Conversions! • Kicking (Kilo) • Her (Hecto) • Down (Deka) • May (meter, gram, liter) • Damage (Deci) • Carol’s (Centi) • Mind (Milli) • UP to the LEFT, DOWN to the RIGHT

  6. Calculating Speed • If you know the distance an object travels in a certain amount of time, you can calculate the speed • Speed = Distance Time • Speed: distance object travels per unit of time • Various ways to express speed: m/s or km/h • Average Speed: total distance & total time • Instantaneous Speed: rate at which an object is moving at a given instant time

  7. Velocity & Graphing Motion • A storm is coming at a speed of 25 km/h!!! • Velocity: Speed AND Direction of an object’s motion • What if you want to show somebody motion? • Line Graph: plotting distance (y) vs. time (x) • Slope: steepness of the line • Slope = Rise / Run • Rise: vertical difference between two points • Run: horizontal difference between two points

  8. Motion of Earth’s Plates • Plates: major pieces of Earth’s rocky outer layer • Fit together like puzzle pieces- Pangaea • Theory of Plate Tectonics: Earth’s landmasses have changed position over time because they are part of plates that are moving slowly • Why they movin’? • Heat from below the Earth pushes rock up • The cooler rock gets pushed aside and sinks down • Slow moving action of rock causes plate movement

  9. Plate Movement • OMG! The Plates are gonna collide! • Plates move at a rate of only a few mm-cm each year • Distance = Speed X Time • Distance = 5 cm / year X 1,000 yrs = 5,000 cm

  10. Acceleration • The Crazy Life of a Baseball • Acceleration = Speeding Up….. NOT!!! • Acceleration: rate at which velocity changes • Increase speed, decrease speed, change direction- examples?? • Can an object at a constant speed accelerate? • Yes!! changing lanes, running a curve, ferris wheel

  11. Calculating Acceleration • Acceleration = Final Speed – Initial Speed Time • Units: meters/sec per second m/s2 • Let’s Practice! • The Black Eyed Peas private plane is about to take off. It reaches a final speed on the runway of 40 m/s after 5 seconds. What is the acceleration of the plane?

  12. Graphing Acceleration What can we tell from this graph? Increasing Speed Constant Acceleration

  13. Graphing Acceleration What can we tell from this graph? Curve= a Each second traveled a greater distance & speed than the second before Speed Increasing

  14. Forces • Force: a push or pull described by its strength and direction • Newton (N): SI Unit used for measuring the strength of a force • Exert about 1 N when lifting up a lemon • We represent forces using arrows • Arrows point in the direction of the force • Length of arrow tells strength- Longer = Bigger F

  15. Combining Forces • Net Force: combination of all forces acting on an object • Determines if an object moves • Determines which direction an object moves 5 N 5 N = 10 N 5 N 10 N 5 N = 5 N 5 N = 0

  16. Unbalanced & Balanced Forces • UnbalancedForce: a net force acting on an object causing it to start or stopmoving or change direction • Causes a change in the object’s motion • Balanced Forces: equal forces acting on one object in opposite directions • Causes no change in the object’s motion Unbalanced Unbalanced Balanced 5 N 5 N 5 N 5 N = 10 N 5 N 10 N 10 N 10 N 10 N = 5 N 5 N 5 N 5 N 5 N 5 N 5 N 5 N 5 N 5 N 5 N 5 N = = = = 0 0 0 0

  17. Friction • Friction: force that 2 objects exert on each other when they rub together • Strength of the force of friction depends on: • 1.) How hard the surfaces push together • 2.) The types of surfaces involved • Let’s try it! Rub your hands together • Friction always acts in the opposite direction to the direction of the objects motion • Metal Slides… Yikes! • Without friction, moving objects might not stop until it hits another object

  18. Types of Friction • Static: acts on objects that aren’t moving • requires extra force to start motion of objects at rest • Moving a Desk & Body Builders moving cars • Sliding: two solid surfaces slide over each other • Sand on ice, chalk on hands, brakes of bike

  19. Types of Friction • Rolling: objects roll across a surface • Easier to overcome than sliding friction • Skateboards & Bikes use ball bearings • Fluid: solid objects move through a fluid • Easier to overcome than sliding friction • Use of water, oil, or air • WD40 (oil), streamlined helmet (air), hairy legs (Water) eek!

  20. Gravity • Gravity: force that pulls objects toward each other • Issac Newton- Law of Universal Gravitation • Gravity acts everywhere in the universe! • A force acts to pull objects straight down toward the center of Earth • The Famous Apple!

  21. Factors of Gravity, Weight, & Mass • 2 Things Affect Gravitational Attraction • Mass- amount of matter in an object (gram) • More mass = Great Gravitational Force • Distance • Farther apart = Less Gravitational Force • Mass & Weight are NOT the SAME • Weight- measure of gravitational force exerted • Force of gravity on person/object at surface of a planet • Weight varies w/ strength of gravities force, mass doesn’t

  22. Gravity & Motion • Free Fall: motion of a falling object when the only force acting on it is gravity • Force of gravity is unbalanced • Objects in free fall are accelerating • Acceleration due to gravity on Earth = 9.8 m/s2 • All objects in free fall accelerate at the same rate regardless of mass

  23. Gravity & Motion • Air Resistance: fluid friction experienced by objects falling through the air • Upward force exerted on all falling objects in air • Objects with more surface area = more resistance • Air resistance increases with velocity • As object speeds up, resistance gets greater & greater • Eventually force of air resistance & gravity are equal • Force is balanced, no acceleration, constant velocity • Terminal Velocity: greatest velocity a falling object reaches when force of air resistance equals weight of object • An object that is thrown vertically will land at the same time as an object that was dropped

  24. First Law of Motion- Inertia • An object at rest will remain at rest, and an object moving at a constant velocity will remain moving at a constant velocity unless it is acted upon by an unbalanced (net) force • Tennis Game- Ball moves until gravity or friction change objects motion • If an object is not moving, it will not move until a force acts on it • Clothes on your bedroom floor!

  25. Inertia • Inertia: tendency of object to resist change in motion • Greater the mass of object = Greater Inertia = Greater force needed to change its motion

  26. Second Law of Motion • Acceleration depends on the object’s mass and on the force acting on the object • Force = Mass X Acceleration F = M x A • Unit of Force = Newtons (N) • Increase Acceleration = Increase Force • Increase Mass = Decrease Acceleration • Boo Yah! Practice Problem! • You are cruzin’ the streets of Mattoon with an acceleration of 20 m/s in your Lamborghini that has a mass of 1250 kg. What is the net force?

  27. Third Law of Motion • If one object exerts a force on another object, then the second object exerts a force of equal strength in the opposite direction of the first object…. What???? • For every action there is an equal but opposite reaction • Action Reaction Pairs: Examples…?

  28. Action Reaction Forces Cancel? • “Ms. Genta, you said before, forces with equal and opposite direction cancel out and cause no movement…??? You must be trippin!” • Don’t Cancel If Acting on DIFFERENT objects!

  29. Momentum • Momentum: quantity of motion • Momentum = Mass x Velocity (kg m/s) • Momentum of an object is in the same direction as its velocity • More Momentum = Harder to Stop • What same velocity, different mass? • Car & Baseball both moving at 20 m/s • Law of Conservation of Momentum: in the absence of outside forces, it can be transferred from one object to another, but none is lost

  30. Momentum & Collisions

  31. Rocket Motion • Rockets rise into the air because it expels gases with a downward force, then the gases exert an equal but opposite reaction force on the rocket • Upward thrust is greater than downward gravity • Centripetal force: causes an object to move in a circle • Force on satellites that are accelerating & revolving around Earth • Satellites in orbit around Earth continuously fall towards Earth, but because Earth is curved they travel around it

  32. What is Work? • Work: force exerted on an object causing it to move in the same direction as the force • Pushing a swing, lifting bags up, pulling blinds down • It is not work unless the object moves! • Pushing a car, lifting an enormous boulder • It is not work unless the motion is in the same direction as the force • Carrying your books to class • The good news: Homework is not work!! 

  33. Calculating Work • The amount of work you do depends on both the amount of force you exert and the distance the object moves • Work = force X distance • Measured in Joules (J) • Work done to exert a force of 1 Newton/ 1 Meter • Heavier Object = Greater Work • Greater Distance = Greater Work • Let’s Practice! • An old, precious lady asks you to move her 95 N sewing kit a distance of 12 m. How much work are you going to have to exert?

  34. Power • If 1 person sprints up the stairs with a box and 1 person creeps up the stairs with the same box, you are doing the same amount of work but…. • Power: the amount of work done on an object in a unit of time • Power = Work or Power = Force X Distance Time Time • Unit of Power: Watts (W) = 1 J/s • So… more power to sprint up the stairs! • Mr. Smith exerts a force of 900 N to push a cart of ice cream down to Ms. Genta’s amazing science students! Oh Ya! The cart moves 250 meters in 40 seconds. What is the power of Mr. Smith?

  35. What is a Machine? • Machine: device that allows work to be easier • Hands, shovel, wheelbarrow, crane • Machines make work easier by changing either the force, distance, or direction • Input Force: force exerted on the machine • Input force moves machine- input distance • Output Force: force machine exerts on object • Machine exerts a force- output distance • Input Work = Input Force X Input Distance • Output work is never greater than Input work

  36. Mechanical Advantage • Mechanical Advantage = Output Force Input Force • Mechanical Advantage the number of times a machines increases a force exerted on it • Increase Force: M.A greater than 1 • You input 10 N on a can opener • Can opener outputs 30 N on the can • Mechanical advantage of 3 • Increase Distance : M.A less than 1 • You input 20 N on a stress ball • Stress ball outputs 10 N on your hand • Mechanical advantage of 0.5 • Changing Direction: M.A always equal to 1 • Input force is the same as output force

  37. Efficiency of Machines X 100% • Efficiency: compares output & input • Efficiency = Output Work Input Work • Friction decreases the efficiency of machines • Think about old rusty scissors! • Efficiency of machines, always less than 100% • Practice Time! • Your sweet dad asks you to mow the lawn and pulls the worst lookin’ mower out the garage. I mean this thing was made in 1875. Your input is 250,000 J and the work done by the mower is 100,000 J. How efficient is this machine?

  38. Simple Machines: Inclined Plane • A flat, sloped surface… aka ramp • Exert input force over a longer distance • Input force- pushing or pulling object • Output force- lifting object without inclined plane • Input far less than output • Ideal Mechanical Advantage = Length of incline Height of incline

  39. Simple Machines: Wedge • Thick at one end, gradually goes to a thin edge • Literally moving the inclined plane • Ideal Mechanical Advantage = Length of wedge Width of wedge • Longer, thinner the wedge, greater M.A • Input Force splits into two output forces • Examples: knife, zipper, axe, sharpener, mouth

  40. Simple Machines: Screws • Inclined plane wrapped around cylinder -“spiral” • Threads on a screw act like an incline plane to increase distance over which force is exerted • Screw exerts an outward force on the wood • Closer the threads, greater M.A • Calculating M.A = Length around threads Length around screw • Examples: screws, jar lids, light bulb

  41. Simple Machines: Levers • Bar that is free to pivot or rotate on a fixed point • Fixed point that a lever pivots around: Fulcrum • Three Classes of Levers: • 1.) 1st Class- always change direction of input force • Scissors, pliers, seesaws, paint can opener, lifting neck • 2.) 2nd Class- increase force, no change direction • Wheelbarrow, doors, nutcrackers, bottle openers, walking • 3.) 3rd Class- increase distance, no change force • hockey stick, fishing pole, shovel, baseball bat, flexing

  42. Simple Machines: Wheel & Axle • Two circular objects fastened together that rotate around a common axis • Object with larger radius – Wheel • Object with smaller radius - Axle • Greater the ratio between the radius of the wheel and the radius of the axel- Greater M.A • Mechanical Advantage = Radius of Wheel Radius of Axel • Examples: screwdriver, doorknob, fairy boat

  43. Simple Machines: Pulleys • Grooved wheel with a rope or cable wrapped around it • Fixed Pulley: attached to a structure • Top of flagpole • Moveable Pulley: attached to moving object • Construction Cranes • Block & Tackle: combination of fixed & moveable • Mechanical advantage is equal to the number of sections of rope that supports the object

  44. Compound Machines • Compound machines: use two or more simple machines • Handle- Wheel & Axel • Screw- also part of axel • Wedge- Peels Skin • Lever- suction cup

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