Student Learning Objectives Motion (Chapter 2) Student Learning Objectives Compare and contrast terms used to describe motion Analyze circular and parabolic motion

Physics:The Most Fundamental Physical Science Physics is concerned with the basic principles that describe how the universe works. Physics deals with matter, motion, force, and energy. Intro

Physics – Areas of Study Classical mechanics Waves and sounds Thermodynamics Electromagnetism Quantum mechanics Atomic and nuclear physics Relativity Intro

Motion is everywhere – walking, driving, flying, etc. This chapter focuses on definition/discussion of: speed, velocity, and acceleration. There are two basic kinds of motion: Straight line Circular If SuperPowers Were Real: Super Speed Intro

Defining Motion Position – the location of an object A reference point must be given in order to define the position of an object How fast are you moving right now? - Tucker Hiatt Motion – an object is undergoing a continuous change in position Description of Motion – the time rate of change of position A combination of length and time describes motion Section 2.1

How do speed and velocity compare? Average speed is the amount of distance covered in some amount of time. Time can only go forward Why Does Time Move Forward? Velocity is speed in some direction.   Up, Down Left, Right North, South, East, West –, + s = d t

Vectors Note that vectors may be both positive and negative. Section 2.2

Instantaneous speed Section 2.2

These Practice Problems are presented in class Scalars are quantities that indicate size, indicate a numerical value. Vectors are quantities that indicate the size and direction. The magnitude of a vector is a scalar; it is the size of the vector. Example: 65 mph North

How is acceleration defined? Acceleration is the change of velocity in some amount of time. Deceleration is negative acceleration. (opposite direction of motion) a = Dv t ∆=delta=change http://www.physicsclassroom.com/mmedia/kinema/pvpa.cfm http://www.physicsclassroom.com/mmedia/kinema/pvna.cfm http://www.physicsclassroom.com/mmedia/kinema/avd.cfm

A car that maintains a constant speed in a straight line has zero acceleration. The distance traveled depends on how long the object has been accelerating. d = (1/2)at2

Practice These Practice Problems are presented in class

What causes vertical acceleration? Objects are accelerated downward because of gravity. The gravitational pull from the Earth is the same on all objects, so the downward acceleration is the same on all objects, 9.81 m/s2. Any difference in the net acceleration is due to air resistance. MythBusters Feather and Hammer Drop

Practice These Practice Problems are presented in class

What is terminal velocity? An object in free fall is only affected by gravity (no air resistance). Air resistance provides acceleration upward. Surface area increases air resistance. Speed increases air resistance. Terminal velocity occurs when air resistance balances gravity. What is terminal velocity? http://www.physicsclassroom.com/mmedia/newtlaws/sd.cfm Terminal Velocity

What causes circular motion? In circular motion, a centripetal force (“center-seeking” force) causes a constant change in motion, a constant change in direction. Objects move in a straight line, unless an unbalanced force changes the motion. ac = v2 r Fc = mac http://www.physicsclassroom.com/mmedia/circmot/ucm.cfm

Acceleration in Uniform Circular Motion Although an object in uniform circular motion has a constant speed, it is constantly changing directions and therefore its velocity is constantly changing directions. Since there is a change in direction there is a change in acceleration. What is the direction of this acceleration? It is at right angles to the velocity, and generally points toward the center of the circle.

Centripetal (“center-seeking”) Acceleration Supplied by friction of the tires of a car The car remains in a circular path as long as there is enough centripetal acceleration. Centripetal (“center-seeking”) Acceleration

Practice

Projectile Motion An object thrown horizontally combines both straight-line and vertical motion each of which act independently. Neglecting air resistance, a horizontally projected object travels in a horizontal direction with a constant velocity while falling vertically due to gravity.

An object thrown horizontally will fall at the same rate as an object that is dropped.

The velocity in the horizontal direction does not affect the velocity and acceleration in the vertical direction. Shoot the Monkey

Why does a projectile have a parabolic trajectory? The addition of the horizontal velocity and the vertical acceleration due to gravity results in a curved path. http://science360.gov/obj/tkn-video/fc729ef0-22ee-4f61-bb2a-b6c07685fb02/science-nfl-football-projectile-motion-parabolas

Projected at an angle (not horizontal) Combined Horz/Vert. Components Vertical Component Horizontal Component + =

A projectile's motion in x does not affect its motion in y A projectile's motion in x does not affect its motion in y! (and vice versa) Velocity in x is constant if there is no air resistance. Why? Velocity in y changes. Why? Harvard Shoots and Drops http://www.physicsclassroom.com/mmedia/vectors/hlp.cfm http://www.physicsclassroom.com/mmedia/vectors/pap.cfm

A projectile will fall a vertical distance (y) each second after reaching maximum height. The range (x) of a projectile relative to the horizontal plane depends on the object’s horizontal velocity and time of flight. y = (1/2)gt2 x = vt MythBusters Bullet Dropped and Shot Harvard Shoots the Monkey

Under real-world conditions, air resistance causes the paths to be non-symmetric. Air resistance reduces the horizontal velocity.

Practice

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