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Chapter 8 Motion and Forces

Chapter 8 Motion and Forces. Motion. D. S. T. Motion- a change in position against a stationary background Speed 1. Describes how fast an object moves 2. Calculating speed : distance traveled / time it took to travel that distance

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Chapter 8 Motion and Forces

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  1. Chapter 8Motion and Forces

  2. Motion D S T • Motion- a change in position against a stationary background • Speed 1. Describes how fast an object moves 2. Calculating speed : distance traveled / time it took to travel that distance 3. Calculated speed is always an average or instantaneous speed. 4. Measured in m/s, or km/hr, or mi/hr, etc.

  3. Constant Speed Refers to objects that cover equal amounts of distance in equal amounts of time. Ex. A race car that has a constant speed of 96 m/s travels at a distance of 96m every second

  4. Distance – Time Graphs Moving fast Moving slow At rest Time always goes on the x-axis Distance is always on the y-axis Examples……

  5. Velocity • Same as speed but includes direction -Ex. 45 mi/hr south • Does not have to be a compass direction • Ex. 23 m/s towards third base • Calculated the same way as speed

  6. Momentum 500 kg •m/s east 2000 kg • m/s west • Momentum • Depends on an objects velocity and its mass • P = momentum • P= mass x velocity • Momentum Equation   The SI unit for mass is kg. • The SI unit for velocity is m/s. • The SI unit for momentum is kg x m/s.

  7. Law of conservation of momentum : total momentum of two cars before a collision equals the momentum after the collision

  8. PRACTICE PROBLEMS :   1.  Calculate the momentum of a 0.15 kg ball that is moving toward home plate at a velocity of 40m/s. 2.  Which has greater momentum, a 2.0kg hockey puck moving east at 2.5m/s or a 1.3kg hockey puck moving south at 3.0m/s? 3.  A track athlete throws a 2kg discus into a field with a velocity of 21m/s.  What is the momentum of the discus? 4.  Calculate the momentum of a 700g ball that is rolling down a ramp at 4.6m/s. 5.  A cannon fires a 40.5kg shell toward a target and the shell moves with a velocity of 120m/s.  Calculate the shell's momentum. Feeling pretty good about your abilities?  

  9. Acceleration Acceleration : A change in an object’s velocity. There are 2 ways an object can accelerate… Change its speed Change its direction Equation: a = final velocity –initial velocity time

  10. Acceleration Practice ProblemsPRACTICE PROBLEMS:1.   As a shuttle bus comes to a normal stop, it slows from 9.00m/s to 0.00m/s in 5.00s.  Find the average acceleration of the bus.     2.    During a race, a sprinter increases from 5.0 m/s to 7.5 m/s over a period of 1.25s.  What is the sprinter’s average acceleration during this period?3.   A baby sitter pushing a stroller starts from rest and accelerates at a rate of  0.500m/s2.  What is the velocity of the stroller after it has traveled for 4.75 minutes?   

  11. Practice Problems: Solving for TimeSolving for Time: Marisa’s car accelerates at an average rate of 2.6m/s2.  Calculate how long it takes her car to accelerate from 24.6m/s to 26.8m/s. If a rocket undergoes a constant total acceleration of 6.25m/s2, so that its speed increases from rest to about 750m/s, how long will it take for the rocket to reach 750m/s.   A dog runs with an initial speed of 1.5m/s on a waxed floor.  It slides to a stop with an acceleration of -0.35m/s2.  How long does it take for the dog to come to a stop?

  12. Velocity – Time Graphs Constant Velocity Speeding up Slowing down

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