Quiz 2 8:30-8:50am TODAY Closed book Next lecture January 29 Quiz 3 will cover the material from today’s lecture, FNT’s from DLM 3, material from DLM4 this week, including FNTs for DLM5.

Energy Interaction Model Energy systems Energy is converted from one form to another, but NEVER created nor destroyed. Etherma l Ebond Emovement (KE) Egravit y E electri c E sprin g “Energy” exists in many different forms. Enuclea r

Energy is converted from one form to another, but NEVER created nor destroyed. E therma l E bond Emovement (KE) Egravit y E electri c E sprin g Steam engine E nuclea r Nuclear power plant

Examples of Mechanical Phenomena Emovement (KE) Egravit y E sprin g Rear shock absorber and spring of BMW R75/5 Motorcycle

Kinetic Energy Kinetic energy is “movement energy” the faster something is moving, the more KE it has The direction of the motion of the object is unimportant. Indicator for the Kinetic energy system is “speed” KE = Mathematically, Kinetic energy mass of an object KE Speed Baseba ll Work

Work We introduce a scientific use of the term Work. Work transfer of energy that takes place from a physical system to another physical system due to an interaction that involves “Force”. KESpeed Baseba ll Work The pitcher’s hand “pushed” the baseball. The pitcher’s hand exerted force on the baseball. As a result, the baseball started moving (its KE increased).

May the Force Be With You "an energy field, created by all living things, that surrounds us, penetrates us, and binds the galaxy together."

Force To be more precise, we need the concept of “Force” : “Push” or “Pull” An overall push (or pull!) in the direction the object is travelling has the effect of speeding it up. 1) Block is already moving, you push in same direction: direction of travel direction of Force KESpeed Work Consider a block being pushed by you on a level surface with no friction:

Force To be more precise, we need the concept of “Force” : “Push” or “Pull” Consider a block being pushed by you on a level surface with no friction: 2) Block is already moving, you push in opposite direction: direction of travel direction of Force KESpeed Work An overall push (or pull!) in against the direction the object is travelling has the effect of slowing it down.

Work What’s force to do with work? Work transfer of energy into or out of a physical system by a force exerted by another physical system. The change in energy results from an interaction in which an object moves through a distance parallel to the force exerted on it. Work = F parallel ∆x = F || ∆x [Joule] = [Newton] [m]=[Nm]

Work How much energy was transferred to the KE system of the baseball in form of Work? KESpeed Baseba ll Work (290 J, assume v=100mph=44m/s, m=0.3kg) 1.Conservation of Energy says… ∆KE = Work ∆KE = KE final - KE initial =1/2(m)(v f 2 ) What about force? Work = F || ∆ x= F || (1m) F || = 290 N

Force Properties of forces Force is a vector quantity i.e. Forces have both magnitude and direction

Force To be more precise, we need the concept of “Force” : “Push” or “Pull” An overall push (or pull!) in the direction the object is travelling has the effect of speeding it up. 1) Block is already moving, you push in same direction: direction of travel direction of Force Consider a block being pushed by you on a level surface with no friction: KESpeed Work

Force To be more precise, we need the concept of “Force” : “Push” or “Pull” An overall push (or pull!) in the direction the object is travelling has the effect of speeding it up. Consider a block being pushed by you on a level surface with no friction: 2) Block is already moving, you push in opposite direction: direction of travel direction of Force KESpeed Work

Force Properties of forces Force is a vector quantity i.e. Forces have both magnitude and direction Force is the agent of interaction of TWO objects e.g. The pitcher’s hand and the baseball The two forces involved in an interaction are opposite and equal (Newton’s Third Law) F hand on the baseball = - F baseball on the hand

Force Properties of forces Force is a vector quantity i.e. Forces have both magnitude and direction Force is the agent of interaction of TWO objects e.g. The pitcher’s hand and the baseball The two forces involved in an interaction are opposite and equal (Newton’s Third Law) F plane on gas = - F gas on plane F plane on gas F gas on plane

Force Properties of forces Force is a vector quantity i.e. Forces have both magnitude and direction Force is the agent of interaction of TWO objects e.g. The pitcher’s hand and the baseball The two forces involved in an interaction are opposite and equal (Newton’s Third Law) Contact force vs non contact force F gravitational

m m v=0 Pull v=0 Mass is pulled part way up a well (like in FNT). This time work is done but there is no change in KE. Work entering or leaving does NOT automatically mean KE is increasing or decreasing. Similar to how heat entering or leaving does NOT automatically mean the temperature is changing.

m m v f =0 Pull v i =0 Work was done on the mass Work = F || ∆x Where did the energy go?? Conservation of Energy says… ∆PE grav = Work = F you on mass ∆height= mg(h final - h initial ) ∆x PE grav Height Work What indicator of the object change? T? Phase? Speed?

Gravitational Potential Energy Gravitational potential energy-system exists for each pair of objects interacting by the gravitational force ∆PE grav only depends on the change in vertical distance that the object moved (I.e. change in the distance between the center of the Earth and the object) ∆PE grav = Mathematically, Usually, we focus on the gravitational potential energy due to the interaction between an object and the Earth. Crumpled Paper PEgrav Height KESpeed Note:we are neglecting the friction

Bowling ball What is the height of the bowling ball after one full swing? (a) Same (b) Higher (c) Lower

Bowling ball When is the speed of the bowling ball maximum (minimum)?

Bowling ball When is the PE grav the bowling ball minimum (maximum)?

Bowling ball PE grav Height KESpeed initial Final(still in motion)

Bowling ball PE grav Height KESpeed Initial (in motion) Final

Bowling ball PE grav Height KESpeed initial Final(still in motion)

Bowling ball PE grav Height KESpeed Initial (still in motion) Final

Mass-Spring

Mass-Spring KESpeed Increase in speed is proportional to the distance the spring was stretched or compressed

Mass-Spring KESpeed Equilibrium position PE mass-spring y (distance from the equilibrium position)

Mass-Spring When is the speed of the mass maximum (minimum)?

Mass-Spring When is the PE mass-spring minimum (maximum)?

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