* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download 4-1_to_4-3 - mrhsluniewskiscience
Center of mass wikipedia , lookup
Velocity-addition formula wikipedia , lookup
Hunting oscillation wikipedia , lookup
Coriolis force wikipedia , lookup
Derivations of the Lorentz transformations wikipedia , lookup
Relativistic mechanics wikipedia , lookup
Length contraction wikipedia , lookup
Modified Newtonian dynamics wikipedia , lookup
Equations of motion wikipedia , lookup
Centripetal force wikipedia , lookup
Newton's theorem of revolving orbits wikipedia , lookup
Classical central-force problem wikipedia , lookup
Work (physics) wikipedia , lookup
Mechanics of planar particle motion wikipedia , lookup
Classical mechanics wikipedia , lookup
Rigid body dynamics wikipedia , lookup
Seismometer wikipedia , lookup
Frame of reference wikipedia , lookup
Fictitious force wikipedia , lookup
Centrifugal force wikipedia , lookup
Chapter 4 Dynamics: Newton’s Laws of Motion Objectives • Apply the Law of Inertia to explain physical phenomena. • Compare and contrast weight and mass. • Use mass and weight units. Units of Chapter 4 • Force • Newton’s First Law of Motion • Mass • Newton’s Second Law of Motion • Newton’s Third Law of Motion • Weight – the Force of Gravity; and the Normal Force Units of Chapter 4 • Solving Problems with Newton’s Laws: Free-Body Diagrams • Applications Involving Friction, Inclines • Problem Solving – A General Approach Newton’s Contributions • Calculus • Light is composed of rainbow colors • Reflecting Telescope • Laws of Motion • Theory of Gravitation 4-1 Force A force is a push or pull. An object at rest needs a force to get it moving; a moving object needs a force to change its velocity. The magnitude of a force can be measured using a spring scale. 4-2 Newton’s First Law of Motion Newton’s first law is often called the law of inertia. Every object continues in its state of rest, or of uniform velocity in a straight line, as long as no net force acts on it. Demo – 1st law Period 1 stopped here Forces may be balanced or unbalanced • Balanced forces – all forces acting on an object are equal – There is NO MOTION • Unbalanced forces – one or more forces acting on an object are stronger than others – There is MOTION • A NET FORCE Balanced Force Equal forces in opposite directions produce no motion Unbalanced Forces Unequal opposing forces produce an unbalanced force causing motion If objects in motion tend to stay in motion, why don’t moving objects keep moving forever? Things don’t keep moving forever because there’s almost always an unbalanced force acting upon them. A book sliding across a table slows down and stops because of the force of friction. If you throw a ball upwards it will eventually slow down and fall because of the force of gravity. 4-2 Newton’s First Law of Motion Inertial reference frames: An inertial reference frame is one in which Newton’s first law is valid. This excludes rotating and accelerating frames. Inertial frames of reference • Inertial reference frames are reference frames in which Newton’s laws hold • From Newton’s 1st law: – If an object experiences no net force, the object either remains at rest or continues with constant speed in a straight line • The Earth is not an inertial frame (it rotates) but is close enough to be considered an inertial frame 15 Inertial frames of reference • Inertia is a property of matter • It is that property of matter which opposes changes in velocity • So, one must centre one's physics reasoning on these thoughts: – An object's velocity will not change all on its own. – Pushes, or pulls, are necessary to change an object's velocity. 16 Inertial frames of reference • There are several ways to describe an inertial frame. Here are a few descriptions: – An inertial frame of reference is a frame of reference with constant velocity. – An inertial frame of reference is a non-accelerating frame of reference. – An inertial frame of reference is a frame of reference in which the law of inertia holds. – An inertial frame of reference is a frame of reference in which Newton's laws of motion hold. – In an inertial frame of reference no fictitious forces arise. 17 First Law Newton’s first law says that with no net force there is no acceleration. • Objects at rest • Objects at constant velocity If there is no observed acceleration on an object with no net force, the observer is in an inertial reference frame. • Newton’s laws of mechanics apply equally • No absolute motion Inertial Frame An observer on the table sees two ball fall. • First straight down • Second in a parabola An observer with speed vx0 sees the reverse. • Second straight down • First in a backwards parabola Both frames are inertial. • Motion consistent with Newton Accelerated Frame A rotating observer throws a ball across a merry-go-round. • Ball veers to the side • No external force This is a non-inertial frame. • Observed motion inconsistent with Newton’s laws • Fictitious forces Newton clarified the mechanics of motion in the “real world”. He believed that there existed an absolute (not accelerating) reference frame, and an absolute time. Inertial reference His laws applied only when measurements were made in this frame reference frame….. …or in any other reference frame that was at rest or moving at a constant velocity relative to this absolute frame. The laws of physics are always the same in any inertial reference frame. 4-3 Mass Mass is the measure of inertia of an object. It is the measure of the amount of matter in an object. In the SI system, mass is measured in kilograms. Mass is not weight: Mass is a property of an object. Weight is the force exerted on that object by gravity. If you go to the moon, whose gravitational acceleration is about 1/6 g, you will weigh much less. Your mass, however, will be the same. Mass: A measure of Inertia • Kick the can. • Kick the same can full of soda. • Kick the same can full of concrete. • Mass is not volume! • Mass is not weight! • The more mass an object has, the greater its inertia and the more force it takes to change its state of motion. Objects at Rest • Objects at rest tend to stay at rest unless acted upon by a force. [push or pull] • Newton described this tendency as inertia. • Inertia can be described as the tendency of an object to keep doing whatever’s it’s doing. Mass & Inertia Which vehicle has more inertia? • Mass is the amount of matter in an object. • The more MASS an object has, the more INERTIA the object has. • Bigger objects are harder to start & stop Slide from www.science- Newton’s 1st Law (also known as the law of inertia) • A moving object moves in a straight line with constant speed unless a force acts on it. • The tendency of an object at rest to remain at rest and an object in motion to remain in motion unless acted upon by an unbalanced force. • Objects do not change their motion unless a force acts on them The truck is in motion. What is the force that causes it to stop? The push of the stopped car. The car is at rest. What is the force that causes it to move? The push of the truck. Slide from www.science- Newton’s First Law (law of inertia) • INERTIA is a property of an object that describes how much ______________________ it will resist change to the motion of the object • more _____ ____ mass means more inertia 1st Law • Unless acted upon by an unbalanced force, this golf ball would sit on the tee forever. What is this unbalanced force that acts on an object in motion? • There are four main types of friction: – Sliding friction: ice skating – Rolling friction: bowling – Fluid friction (air or liquid): air or water resistance – Static friction: initial friction when moving an object 1st Law • Once airborne, unless acted on by an unbalanced force (gravity and air – fluid friction) it would never stop! Inertia Newton’s First Law When the motorcycle stops, the rider continues his motion. Terminal Velocity Exploration • Mass and Weight Lab (No lab write up.) Homework • Newton’s 1st law hand-out • Questions p. 97 1, 2 Closure • When the pellet fired into the spiral tube emerges, which path will it follow? (neglect gravity) Answer • While in the tube, it is forced to curve, but when it gets outside, no force is exerted on the pellet and (law of inertia) it follows a straight – line path…B! Elaboration Computer Activity for Newton’s First Law • http://www.physicsclassroom.com/Class/n ewtlaws/u2l1a.cfm Inertia Evaluation • Carpenters use different hammers for different jobs. A tack hammer is a light hammer used for small nails in delicate situations. A regular hammer is heavier and is used for larger nails in building walls. Compare the two hammers using Newton’s 1st law in terms of the hammers’ function, advantages and disadvantages.