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Friday PS Test Review Hand in day Work/power

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Hand in Yellow workbook Seat-belt position paper

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Review for test on Monday Forces Definition- any push or pull on an object Units are NEWTONS Identification Applied forces Friction Gravitational forces Magnetic, electric forces

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Forces Balanced forces = when all the forces acting on an object cancel each other out Unbalanced forces = when all the forces do not cancel each other out (more force on object in one direction than in others)

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Net force The combination of all forces on an object For balanced forces F net = 0 –At rest or at constant velocity For unbalanced forces F net ≠ 0 –acceleration

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Weight, mass Weight = the force due to gravitational pull on an object W = mg g = 10 m/s 2 on earth Mass = the amount of matter that makes up an object Differences? Similarities?

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Inertia Is the measure of an objects resistance to change in its motion Directly related to the amount of mass

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Newton’s 3 laws !st 2 nd 3 rd When does an object change its motion (accelerate)?

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Collisions and the laws Be able to use the laws of motion to explain what happens in different types of collisions Front crash Rear crash At least 2 reasons for head rests Does the bus and the car exert the same amount of force on each other? Why are people less injured on the bus?

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Collisions and the laws Seat-belt configurations What is wrong with just lap-belts? Why are seat-belts flat and wide? What are uses for EKG’s, MRI’s and Xrays?

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Free body diagrams FBD’s purpose: To visually show how the forces are arranged on an object Components of a free-body diagram –Forces –Object –Direction arrow

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FBD Where do all but the direction arrow originate in the diagram? How are the forces of air resistance or friction drawn on FBD? How is the force of gravity drawn on any FBD?

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2nd law problems Using F net = ma Units for each part are…? Triangle set-up

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Advanced 2 nd law problems #1 Have to use the acceleration equation first then use 2 nd law #2 Have to determine F net first, then use 2 nd law

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Example Nicole slows down in her BMW from 15 m/s to 3 m/s in 42 seconds. What is the mass of her car if the net force on it is 7312 N?

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Law Universal Gravitation There is a gravitational attraction between any two items that have mass. The amount of the force is related to the mass of each object and the distance their centers are apart More mass, less distance greater force

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Free Fall Any object that moves under the influence of only the force due to gravity Thrown, Dropped objects Acceleration = 10 m/s 2 or (9.8)

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Terminal velocity The maximum velocity reached by a dropped object Occurs when the downward gravitational force is matched by the upward force of air resistance Air resistance depends on surface area and speed of object

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Action and reaction forces Identification in the real world Equal and opposite Applied to different objects May have different effects

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Momentum A quantity of motion The value of an objects mass times its velocity To have momentum the object has to be ___________.

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Change in momentum To change an object’s momentum requires a net force being applied The greater the force and the longer the time applied the bigger change in momentum Baseball/softball examples Fender benders vs totaling the car

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Momentum change in a accident The amount of change in momentum is constant Change can be brought about different ways More time less force Less time more force Seat Belts, crumple zones, air bags, Padded dashboards

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Conservation of momentum In a system, momentum can not be created or destroyed, but can be transferred Momentum is direction oriented Billiards balls

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Metric conversion km _________ mm

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What is the difference between distance and displacement?

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Homework P Problems 7-11 Problems Problems 32,34,39,40

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Answers to homework P B 8D 9B 10D 11A

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18 Free fall means there is only the force of gravity Weightlessness = no force of gravity 19 less force of gravity, so acceleration due to gravity is less than when the upward force of air resistance = force of gravity

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32 a 195 kg m/s 32 b 440 kg m/s 32 c 0 kg m/s 32 d 12 kg m/s 34 gravitational force is much less (1/16 th ) 39 acceleration would be doubled 40 a. Train, b. ball, c. equal, equal but opposite

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