Physics Lecture Outline PDF

Physics—The Basic Science Physical sciences include geology, astronomy, chemistry, and physics. Life sciences include biology, zoology, and botany. Physics underlies all the sciences. Fundamental and derived quantities - Measurement | Term 1 Unit 1 | 7th Science (brainkart.com) ...

Physics—The Basic Science Physical sciences include geology, astronomy, chemistry, and physics. Life sciences include biology, zoology, and botany. Physics underlies all the sciences. Fundamental and derived quantities - Measurement | Term 1 Unit 1 | 7th Science (brainkart.com)  MKS is also known as SI units or metric system © 2015 Pearson Education, Inc.  List one of your hobbies © 2015 Pearson Education, Inc.  Which “app” in your phone is something you need very much? © 2015 Pearson Education, Inc.  Newton's Law of Inertia (pearsoncmg.com) Based on the video demonstrated by the author, what is meant by the term INERTIA ? 1. Inertia is a fundamental quantity 2. Inertia is a force 3. Inertia is a physical property of an object 4. Inertia is the definition of an object having a force © 2015 Pearson Education, Inc.  The Old Tablecloth Trick (pearsoncmg.com) According to the video watched, the author was able to remove the cloth from the table without any disturbance to the cups and plates. What is the physics of this trick? 1. Newton’s first law or inertia 2. Newton’s second law 3. Newton’s third law 4. Force given by the author © 2015 Pearson Education, Inc.  Based on the video by Brain Cox visiting the lab where a ball and feather is dropped in vacuum, Which one falls first? a.ball b. feather c. Both will fall at the same time d. No way to say. © 2015 Pearson Education, Inc.  Based on the video by the person with a hammer and feather, in a room with air resistance Which one falls first? a. hammer b. feather c. Both will fall at the same time d. No way to say. © 2015 Pearson Education, Inc.  Based on the video by the person with a hammer and feather, in MOON Which one falls first? a. hammer b. feather c. Both will fall at the same time d. No way to say. © 2015 Pearson Education, Inc.  Based on the video by the person with a heavy hammer and light hammer, Which one falls first? a. Heavy hammer b. Light hammer c. Both will fall at the same time d. No way to say. © 2015 Pearson Education, Inc.  A ball and a feather are dropped in vacuum. Which one falls first? ball feather Both will fall at the same time No way to say. © 2015 Pearson Education, Inc.  A ball and a feather are dropped from the top of a tall building. Air drag does affect motion. The ball that experiences the greater amount of air drag is the ball feather Neither, for both experience the same amount of air resistance. No way to say. © 2015 Pearson Education, Inc.  The amount of air resistance that acts on a sky diver depends on the diver's 1. area. 2. speed. 3. Both area and speed. 4. acceleration. © 2015 Pearson Education, Inc.  The amount of air resistance that acts on a diver depends on the diver's area. speed. area and speed. acceleration. © 2015 Pearson Education, Inc. Nonfree Fall As the skydiver falls faster and faster through the air, what forces act on the sky diver A. Only weight B. Only air resistance C. Weight and air resistance D. Gravity or acceleration due to gravity and air resistance Nonfree Fall As the skydiver falls faster and faster through the air, air resistance A. increases. B. decreases. C. remains the same. D. Not enough information. Nonfree Fall CHECK YOUR ANSWER As the skydiver falls faster and faster through the air, air resistance A. increases. B. decreases. C. remains the same. D. Not enough information.  What is terminal velocity 1. Air resistance equal the weight of the object 2. Air resistance is greater than the weight of the object 3. Air resistance is lesser than the weight of the object 4. Air resistance is equal to the velocity of the object 5. Air resistance is greater than the mass of the object © 2015 Pearson Education, Inc. Free Fall—How Fast? Based on the video by the author The velocity acquired by an object starting from rest is At a particular instant a free-falling object has a speed of 30 m/s. Exactly 1 s later its speed will be A. the same. B. 35 m/s. C. more than 35 m/s. D. 60 m/s. Free Fall—How Far? Based on the video by the author The distance covered by an accelerating object starting from rest is What is the distance fallen after 4 s for a freely falling object starting from rest? A. 4 m B. 16 m C. 40 m D. 80 m Free Fall—How Far? CHECK YOUR NEIGHBOR What is the distance fallen after 4 s for a freely falling object starting from rest? A. 4m B. 16 m C. 40 m D. 80 m Free Fall—How Far? CHECK YOUR ANSWER What is the distance fallen after 4 s for a freely falling object starting from rest? A. 4m B. 16 m C. 40 m D. 80 m Explanation: Distance = (1/2) × acceleration × time × time So: Distance = (1/2) × 10 m/s2 × 4 s × 4 s So: Distance = 80 m  Scalar quantity a quantity whose description requires both magnitude ( just the number with units) Example: Mass, temperature, pressure, area, volume, speed, distance © 2015 Pearson Education, Inc. Vectors Vector quantity has magnitude and direction. is represented by an arrow. Example: velocity, force, acceleration Scalar quantity has magnitude. Example: mass, volume, speed  Which of the following is a scalar? 1. Force 2. Temperature 3. Velocity 4. acceleration © 2015 Pearson Education, Inc. Lecture Outline Chapter 2: Newton's First Law of Motion—Inertia This lecture will help you understand: Aristotle's Ideas of Motion Galileo's Concept of Inertia Newton's First Law of Motion Net Force and Vectors The Equilibrium Rule Support Force Equilibrium of Moving Things The Moving Earth Aristotle's Ideas of Motion Vs Galileo Ideas Natural motion Galileo demolished Aristotle's assertions – Straight up or straight down for in the 1500s. all things on Earth – Beyond Earth, motion is circular Galileo's discovery: – Example: The Sun and Moon Objects of different weight fall to the continually circle Earth. ground at the same time in the absence of air resistance. Violent motion A moving object needs no force to – Produced by external pushes or keep it moving in the absence of pulls on objects friction. – Example: Wind imposes motion on ships. Galileo's Concept of Inertia Force ( Vector quantity, has the unit of Newton) is a push or a pull Force = mass * acceleration ( from Newton’s second law) Inertia ( there are no units as it is not a physical quantity) is a property of matter to resist changes in motion. depends on the amount of matter in an object (its mass). Galileo's Concept of Inertia Balls rolling on downward-sloping planes pick up speed. Balls rolling on upward-sloping planes lose speed. So a ball on a horizontal plane maintains its speed indefinitely. If the ball comes to rest, it is not due to its "nature," but due to friction. Above experiments laid the foundation to discover the property inertia Mass and Weight Mass: The quantity of matter in an object. It is also the measure of the inertia or sluggishness that an object exhibits in response to any effort made to start it, stop it, or change its state of motion in any way. Weight: Usually the force upon an object due to gravity. Mass and Weight Mass – A measure of the inertia of a material object – Independent of gravity Greater inertia  greater mass – Unit of measurement is the kilogram (kg) Weight (W = mass * acceleration due to gravity) – Usually the force on an object due to gravity – Scientific unit of force is the newton (N)- metric system – Unit is also the pound (lb)- CGS system Mass and Weight Mass and weight in everyday conversation are interchangeable. Mass, however, is different and more fundamental than weight. Mass versus weight – On the Moon and Earth: Weight of an object on the Moon is less than on Earth. Mass of an object is the same in both locations. Mass and Weight 1 kilogram weighs 10 newtons (9.8 newtons, to be precise). Relationship between kilograms and pounds: – 1 kg = 2.2 lb = 10 N at Earth's surface – 1 lb = 4.45 N Working it out: Weight  As a numerical example, let’s calculate the weight of a child with a mass of 25 kg. W mg (25 kg)(10 m/s 2 ) 250 N  Therefore, the child has a weight of 250 N (about 55 lb).  This process can be reversed to obtain the mass of a dog that has a weight of 150 N: W 150 N m  15 kg g 10 m/s 2 Newton's First Law of Motion Every object continues in a state of rest or of uniform speed in a straight line unless acted on by a nonzero net force. Net Force Net force is the combination of all forces that act on an object. – Example: Two 5-N pulls in the same direction produce a 10-N pull (net force of 10 N). If the pair of 5-N pulls are in opposite directions, the net force is zero. Net Force CHECK YOUR NEIGHBOR A cart is pulled to the right with a force of 15 N while being pulled to the left with a force of 20 N. The net force on the cart is A. 5 N to the left. B. 5 N to the right. C. 25 N to the left. D. 25 N to the right.  Net Force CHECK YOUR ANSWER A cart is pulled to the right with a force of 15 N while being pulled to the left with a force of 20 N. The net force on the cart is A. 5 N to the left. The two forces are in opposite B. 5 N to the right. directions, so they subtract. C. 25 N to the left. The direction is determined by D. 25 N to the right. the direction of the larger force. © 2015 Pearson Education, Inc. Net Force CHECK YOUR NEIGHBOR What is the net force acting on the box? A. 15 N to the left B. 15 N to the right C. 5 N to the left D. 5 N to the right ? Net Force CHECK YOUR ANSWER What is the net force acting on the box? A. 15 N to the left B. 15 N to the right C. 5 N to the left D. 5 N to the right © 2015 Pearson Education, Inc. Vectors Resultant The sum of two or more vectors – For vectors in the same direction, add arithmetically. – For vectors in opposite directions, subtract arithmetically. – Two vectors that don't act in the same or opposite direction: use parallelogram rule. – Two vectors at right angles to each other use Pythagorean Theorem: R2 = V2 + H2. Vectors Nellie Newton hangs from a rope as shown. Which side has the greater tension? There are three forces acting on Nellie: – her weight, mg, – a tension in the left-hand side of the rope, – and a tension in the right-hand side of the rope. Vectors Because of the different angles, different rope tensions will occur in each side. Nellie hangs in equilibrium, so her weight is supported by two rope tensions, adding vectorially to be equal and opposite to her weight. The parallelogram rule shows that the tension in the right-hand is greater than the tension in the left-hand side of the rope. The Equilibrium Rule: Example A string holding up a bag of flour Two forces act on the bag of flour: – Tension force in string acts upward. – Force due to gravity acts downward. Both are equal in magnitude and opposite in direction. – When added, they cancel to zero. – So, the bag of flour remains at rest. The Equilibrium Rule The vector sum of forces acting on a nonaccelerating object equals zero. In equation form: F = 0. The red arrows represent force vectors. The sum of the two upward force vectors minus the sum of the three bottom force vectors, equals zero. We say the forces cancel to zero, and the system of Burl, Paul, and the staging is in equilibrium. The Equilibrium Rule CHECK YOUR NEIGHBOR The equilibrium rule, F = 0, applies to A. vector quantities. B. scalar quantities. C. Both of the above. D. None of the above. The Equilibrium Rule CHECK YOUR ANSWER The equilibrium rule, F = 0, applies to A. vector quantities. B. scalar quantities. C. Both of the above. D. None of the above. Explanation: Vector addition accounts for + and – quantities. So, two vectors in opposite directions can add to zero. Support Force Support force (normal force) is an upward force on an object that is opposite to the force of gravity. Example: A book on a table compresses atoms in the table, and the compressed atoms produce the support force. Understanding Support Force When you push down on a spring, the spring pushes back up on you. Similarly, when a book pushes down on a table, the table pushes back up on the book. Equilibrium of Moving Things Equilibrium: a state of no change with no net force acting – Static equilibrium – Example: hockey puck at rest on slippery ice – Dynamic equilibrium – Example: hockey puck sliding at constant speed on slippery ice Equilibrium of Moving Things Equilibrium test: whether something undergoes change in motion – Example: A crate at rest is in static equilibrium (no change in motion). – Example: When pushed at a steady speed, it is in dynamic equilibrium (no change in motion). The Moving Earth Copernicus proposed that Earth was moving, circulating the Sun. This idea was refuted by people. Example: If Earth moved, how could a bird swoop from a branch to catch a worm? Solution: As it swoops, due to inertia, it continues to move sideways at the speed of Earth along with the tree, worm, etc.