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Motion Chapter 8.1 Speed Velocity Momentum

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Speed Distance traveled divided by the time during which motion occurred

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Speed Constant speed means that an object travels the same distance in the same amount of time Objects at rest have a speed of 0 m/s

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Speed Equation Distance Time Speed = v = d t

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Speed Example Suppose a wheelchair racer finishes a 132 m race in 18 s. What was the racer’s average speed?

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Speed Example speed = d/t Speed = 132 meters/18 s Speed = 7.3 m/s

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Are speed and velocity the same? A car travels at a constant speed of 30 miles/hour. The car makes a left at a speed of 30 miles /hour.

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Are speed and velocity the same? Speed did not change Velocity did change

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Velocity Quantity describing both speed and direction Same calculation as speed except that it also designates a direction.

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Velocity Example Find the velocity of a swimmer who swims exactly 110 m toward the shore in 72 s.

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Velocity Example V = d/t V = 110 meters/72 seconds Speed = 1.5 m/s Velocity = 1.5 m/s towards the shore

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Momentum A quantity defined as the product of an object’s mass and its velocity The greater the mass or the faster the velocity, the greater the momentum

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Momentum Equation Momentum = mass x velocity Equation is p=mv p is used to represent momentum

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Momentum Example Find the momentum of a 75 kg speed skater moving forward at 16 m/s.

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Momentum Example momentum = mv Momentum = (75 kg)(16m/s) Momentum= 1200 kg m/s forward

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Conservation of Momentum The total amount of momentum in a system is conserved

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Conservation of Momentum If two vehicles with different masses are traveling with different velocities and they hit head on, the momentum of the two cars before the collision is the same after the collision.

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Acceleration and Force - Chapter 8.2 Acceleration Force Friction and Air-resistance Gravity

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Acceleration change in velocity divided by the time in which the change occurred The greater the acceleration the faster the object is speeding up.

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Acceleration If the speed remains constant, acceleration is zero. SI unit is meter/second per second (m/s/s or m/s 2 )

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Acceleration Equation ∆ velocity Time Acceleration = a = V f -v i ΔtΔt

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Acceleration Example Find the acceleration of a northbound subway train that slows down from 12 m/s to 9.6 m/s in 0.8 s.

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Acceleration Example a = change in v/t Acceleration = (9.6 – 12m/s)/0.8s Acceleration = -3 m/s 2 or m/s/s

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For constant velocity Zero Acceleration

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Accelerating has positive slope

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decelerating has a negative slope

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Force The cause of acceleration or the change in an object’s velocity SI unit of force is a newton. (N)

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Force Two Types: 1. Balanced forces do not change motion

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Force 2. Unbalanced forces result in a net movement in one direction. This occurs because the net force on one side is less than the net force on the other.(ex. Tug of War.)

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Friction the force between two objects in contact that opposes the motion of either object friction maintains balanced forces

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Gravity Gravitational force is determined by the distance between the two masses. Everything falls at an acceleration of 9.8 m/s 2 in the absence of air resistance Gravity is opposed by air resistance

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Gravity Experiments The Physics of Falling

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Horizontal motion has no affect on gravity

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Gravity has no affect on horizontal motion.

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Gravity only works if you look down. True or False

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FALSE

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Air Resistance Air resistance is a form of friction Air resistance opposes gravity. Objects with bigger volumes or smaller densities can experience more air resistance.

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Laws of Motion - Chapter 8.3 Newton’s 1 st Law Newton’s 2 nd Law Newton’s 3 rd Law

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Newton’s 1 st Law unbalanced An object at rest remains at rest and an object in motion maintains its velocity unless it experiences an unbalanced force. Inertia

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How does this work?

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Inertia and a roller coaster

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Newton’s 2 nd Law The unbalanced force acting on an object equals the object’s mass times its acceleration. F=ma

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Measuring Force Force is measured in newtons. 1 N=1 kg*m/s 2

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Force Example What is the force necessary for a 16000 kg automobile to accelerate forward at 2.0 m/s 2 ?

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Force Example Force= ma Force = (16000 kg)(2.0m/s 2 ) Force = 32000 N

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Free Fall the motion of a body when only the force of gravity is acting on it. Acceleration of gravity is 9.8m/s 2 Everything will fall at this acceleration

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Mass vs. Weight Mass represents the measured amount of matter in an object. Weight is the gravitational force an objects experiences based on its mass.

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Mass vs. Weight Weight = mass x gravity w=mg, weight is a force.

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Terminal Velocity The maximum velocity reached by a falling object.

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Terminal Velocity This occurs when air resistance is equal to the force due to gravity. Terminal Velocity of a skydiver is ~200 miles/hr

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Newton’s third Law For every action there is an equal and opposite reaction Rockets move as a result of action and reaction.

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