PHY 107 1st Edition Lecture 11Outline of Last Lecture I. Newton’s Laws of Motion Outline of Current LectureII. Newton’s Laws of Motion (cont.)Current LectureNewton’s Three Laws of Motion: - Describe physical phenomena of a vast range including motion of objects from proteins and cells to stars and planets- Once friction was recognized to be a force, Newton proposed his first law:o If no force acts on a body, the body’s velocity cannot change (the body’s acceleration is zero)- Newton’s Second Law – the relation between the net force (Fnet), mass (m) and acceleration (a); ´Fnet = m´aoFnet , x = maxFnet , y = mayFnet , z = maz- Commonly encountered forces in mechanics:o Gravitational force – force that the earth exerts on any object, directed towards the center of the earth-´Fg = m´a = -mg´j|´Fg| = mgo Weight – the magnitude of the force required to prevent a body from falling freely (NOT the same as mass)-´Fnet , y = W – mg = may = 0 → W = mgo Contact forces – act between 2 objects that are in contact- Have 2 components:- Normal force – acting along the normal to the contact surface- Frictional force – acting parallel to the contact surfaceo Normal force – when a body presses against a surface, the surface deforms and pushes back on the body with a normal force perpendicular to the contact surface- Ex. A block of mass m rests on a table:-´Fnet , y = FN – mg = may = 0 → FN = mg (FN is not always equal to mg)These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.o Friction – if we slide or attempt to slide an object over a surface, the motion is resisted by a bonding between the object and the surface known as “friction”o Tension – the force exerted by a rope attached to an object with the following characteristics:- It is always directed along the rope (not normal to)- It is always pulling the object (not pushing)- It has the same value along the rope - These assumptions can be made:- The rope has negligible mass - The rope does not stretch- If a pulley is used with a rope, we may assume that the pulley is massless and frictionless - Newton’s Third Law – when two bodies interact by exerting forces on each other, the two forces are equal in magnitude and opposite in direction - Ex. A book is leaning against a crate. The force exerted on the crate by the book is´FCB and the force exerted on the book by the crate is ´FBC. The two forces, taken together, are known as a “third – law force pair.” ´FBC = -´FCB- Inertial reference frames – a reference frame is “inertial” if Newton’s three laws of motion hold (so reference frames where Newton’s three laws do not hold are non-inertial”)o At least one inertial reference frame, R, existso Any other reference frame R’ that moves with constant velocity with respect to R is also an inertial reference frame ´aPR = ´aPR 'o A reference frame R’’ which accelerates with respect to R is a non-inertial reference frame ´aPR ≠´aPR 'o The earth is approximately an inertial reference frame (ignoring its rotation)- Free body diagrams:How to draw one: o Choose a set of objects called the “system” o Choose axes and draw all the forces that act on the system by external agents (omitting internal forces because internal forces form third-law pairs which cancel out ´FBA = -´FAB → ´FBA + ´FAB = 0)o Ex. Two blocks, A and B, on which an external force ´Fappis exerted, the followingsystems can be made.xy- System = block A + block B. External forces: ´Fapp = (mA + mB)´a- System = block A. External forces: ´Fapp + = mA´a- System = block B. External forces: ´FBA = mB´a- Recipe for the application of Newton’s Laws of Motion:1. Choose the system to be studied2. Make a simple sketch of the system3. Choose a convenient coordinate system4. Identify all external forces that act on the system and label them on the diagram, ignore all other forces.5. Apply Newton’s 2nd Law to the system: Fnet , x = max&Fnet , y =