2 FORCE READ Unit 1 Lesson 3 page 28-39 text I Force: simply a push or a pullUnit is newton (N)Can cause an object to change speed and direction (velocity)doesn’t always cause an object to moveTypes of forces:Friction=contact force between two objectsGravity= pulls us to Earth, acts at a distanceMagnetic Force= acts at a distance, push or pull
3 Causes of FrictionAdhesion is the molecular force resulting when two materials are brought into close contact with each other.Surface roughness is a factor in friction when the materials are rough enough to cause serious abrasion (a.k.a. sandpaper effect)When one or more of the materials is relatively soft, much of the resistance to movement is caused by deformations or a plowing effect.Homework: Demonstrate or explain the 3 causes of friction.
4 AdhesionAdhesion is the molecular force resulting when two materials are brought into close contact with each other.Sticky materials like rubber and adhesive tapeFluids: water droplets sliding down a window.What will happen when you wet a coin on a ramp?
5 Surface RoughnessSurface roughness is a factor in friction when the materials are rough enough to cause serious abrasion.What does each object look like up close?If the surfaces of two hard solids are extremely rough, the "sandpaper effect" may occur.particles of the materials are dislodged from their surfacesAt one time it was thought that the surface roughness of materials was the cause for friction. In reality, it only has a small effect on friction for most materials.
6 Plowing EffectWhen one or more of the materials is relatively soft, much of the resistance to movement is caused by deformations or a plowing effect.Soft materials will deform when under pressure. This also increases the resistance to motion.Standing on a rug you sink slightlyRubber tires deforming on roadWhen materials deform, you must "plow" through to move, thus creating a resistive force.
7 How can you increase frictional forces? Decrease surface contactIncrease weightStop motionRemove Lubrication
8 How can you increase frictional forces? Decrease surface contact by making the surfaces rougherNot a universal rule b/c two extremely smooth surfaces have increased electrostatic forces b/w them and actually will decrease frictional forcesAdding weight to one object can significantly increase the frictional force between two moving objects
9 Taking them out of motion. Static friction is a different type of friction that indicates the amount of energy required to set an object in motion instead of the energy needed to keep it moving along, which relates to kinetic friction.Static friction always requires more energy to start the object moving than it takes to keep it moving.Remove a lubricantViscous solutions aid in the movement of objects (think oil for squeaking doors)Homework: Demonstrate or explain the 4 ways to increase frictional force.
10 Newton’s Three Laws of Motion An object at rest stay at rest, and an object in motion stays in motion at the same speed and direction, unless it experiences an unbalance force.The acceleration of an object depends on the mass of the object and the amount of force applied.Whenever one object exerts a force on a second object, the second object exerts and equal and opposite force on the first.
11 GravityRead pg U1L4Gravity: is a force of attraction between objects due to their mass; a noncontact forcePulls therefore is an attractive forces9.8 m/s^2
12 Weight Earth’s gravity is felt by you as weight. Weight is a force that depends on massThe force of gravity between Earth and an object is equal to the mass of the object m multiplied by a factor due to gravity gF=mgg= 9.8 m/s^2unit is the same as acceleration thus all objects accelerate toward Earth at the same rate!!!Not a very powerful force
13 Gravity Gravity depends on… Distance Gravitational force decreases as distance increases(Insert diagram from pg. 46)MassGravitational force increases as mass increases
14 WORKUnit 2 L1 Read pgWork: the use of force to move an object some distance in the direction of the forceYou do work when you exert a force on an object and move itOnly done by the part of the force that is in the same direction as the motionCalculated by:W=FxdWork= force x distanceNewton (force) x meter (distance)= newton-meter or joule (J) or work1 joule of work completed when 1 newton of force moves an object 1 meterDefine work and how it is measured
15 WORK, Energy, and Power Energy Ability to cause a change or do work When work is done, energy is transferred, and object must move for work to be doneAlso expressed in joulesPowerThe rate at which work is done or amount of energy transfer2 machines lift the same weight or perform the same work, but the machine with more power does it quickerPower= Energy/ tP= E/tjoules/second or Watts (W)
16 MACHINEs Read Unit 2 Lesson 3 pages 102-113 Machine: any device that helps people do work by changing the way work is done; make tasks easier without decreasing the amount of work doneSimple machines: the machines that make up other machinesThe six simple machinesLevers:Wheels and axlesPulleysInclined planesWedgesScrews
17 MACHINESRemember: work is the use of force to move an object some distanceInput force: the force you apply to the machine through a distanceWork input: the work that you do on a machineWork output: the work done by the machine on an objectOutput force: the force a machine exerts on an objectMechanical advantageMechanical advantage= output force/ input forceA machine that has a M.A.= 1, changes only the direction of the forceA machine that has a M.A.>1, produces greater output forceA machine that has a M.A.<1, requires greater input force, but the output force is applied through a longer distanceMechanical efficiency: a comparison of the machine’s work output with the work input (M.E.= 9work output/ work input)x 100%
18 Simple machinesLever: a bar that pivots at a fixed point called a fulcrum3 classes based on position of fulcrum, load, and input force1st class: fulcrum is between load and input force2nd class: the load is between the fulcrum and the input force3rd class: the input force is between the fulcrum and the loadWheel and axle: made of a wheel connected to a smaller cylindrical object, axleIdeal M.A.= radius input/ radius output
19 Simple machinesPulley: has a grooved wheel that holds a rope or a cable3 typesFixed pulleys: attached to something that does not moveMoveable pulleys: attached to an object being movedBlock and tackle pulleys: combining a fixed and movable pulleyInclined plane: a straight, slanted surfaceIdeal mechanical advantage= length/ heightWedges: a pair of inclined planes that move; have one thick and one thin endScrews: an inclined plane wrapped in a spiral around a cylinder
20 PROJECT Rube Goldberg Challenge Define a task Create a machine using at least 3 simple machines to complete the defined taskWrite at least a one page, double-spaced, 12 point font essay on the simple machines in your machine and Newton’s 3 laws