PHYS 107, Test 1 STUDY GUIDE
PHYS 107, Test 1 STUDY GUIDE Phys 107
Popular in Physical Science I
Popular in Physical Science
This 16 page Study Guide was uploaded by Mallory McClurg on Friday September 16, 2016. The Study Guide belongs to Phys 107 at University of Mississippi taught by Quinn in Fall 2016. Since its upload, it has received 18 views. For similar materials see Physical Science I in Physical Science at University of Mississippi.
Reviews for PHYS 107, Test 1 STUDY GUIDE
Report this Material
What is Karma?
Karma is the currency of StudySoup.
You can buy or earn more Karma at anytime and redeem it for class notes, study guides, flashcards, and more!
Date Created: 09/16/16
Test 1 Study Guide Phys107, Quinn CHAPTER 1: ABOUT SCIENCE What is science? A body of knowledge and a way of thinking that describes the order within the natural world and the causes of that order o Ideas are organized based on observation o Modern science (since the 1500s) expresses those ideas with mathematics, because it’s unambiguous and easy to verify/disprove Disclaimer: science has never proven one thing; instead, many hypotheses have been tested over and over and some have had a constant result, many have not. The only thing science CAN do is DISPROVE hypotheses. Also, scientific theories are not right or wrong; all facts are open to revision. There are no final answers. Important Terms: Fact – scientific facts are revisable data generally agreed upon by competent observers of the same phenomenon Hypothesis – an educated guess based on observation Law – hypothesis that has been tested many times without contradiction Theory – a synthesis of a large body of information, including well- tested and verified hypotheses Model – a representation of something else; an abstract representation of a theory Test Questions… 1. The first scientist to be credited for postulating that Earth circled the Sun was… (Copernicus.) 2. The first scientist to introduce the concept of inertia was… (Galileo.) 3. Whirl a rock at the end of a string and it follows a circular path. If it breaks, the tendency of the rock is to… (follow a straight-line path.) 4. The earliest and most influential Greek philosopher was Aristotle, who among many contributions taught that… (violent motion requires a sustained push or pull; the four elements are earth, water, air, and fire; all motion is either natural or violent.) 5. Inertia is defined as a… (property of matter.) ▯ CHAPTER 2: NEWTON’S FIRST LAW OF MOTION - INERTIA Test 1 Study Guide Phys107, Quinn ▯ Aristotle (384-322 BC) Ideas about Form, Substance, and Matter o Everything on earth is composed of a combination of the 4 “essences”: Earth (solids) Water (liquids) Fire (plasma) Air (gas) Ideas about Motion and Forces o Natural motion – Heavier objects fall faster (proportional to how much “essence” they have) E.g. dropping a ball, dropping a sheet of paper An object will strive to get to its proper place determined by its “essence” Clay naturally falls to the earth; e.g. dropping a ball Smoke naturally rises in air; e.g. lighting a match An object will rest when it is in its proper place o Violent motion – Motion is cause by forces (pushing or pulling) on an object; if there are no forces pushing or pulling an object, it will be in its proper place Pushing a cart; e.g. pushing a book across a table Lifting a weight Wind in a sail Bow and arrow Test 1 Study Guide Phys107, Quinn Ideas about an Object’s Natural Tendency o The natural tendency of an object is to be at rest (in its proper place) Ideas about Earth o Since the earth is in its proper place and there was no conceivable force that could move it, Earth is at rest o Note: “planet” means “wanderer” ▯ ▯ Copernicus (1473-1543) Ideas about Earth o Earth and other planets revolve around the sun ▯ Galileo (1564-1642) Ideas about Motion, Forces, and Friction o Heavier objects do NOT fall faster E.g. dropping a ball; dropping a crumpled (balled up) sheet of paper o A force is required to change the motion of an object moving in a straight line o Friction causes things to slow down and stop E.g. dropping a ball and a feather in a vacuum tube (no air resistance); rolling a smooth ball down an inclined plane onto a tile floor; rolling a rough ball down an inclined plane onto a carpet Ideas bout an Object’s Natural Tendency o The natural tendency of an object is to resist a change in motion (inertia) In the absence of any force, something moving keeps moving in a straight line E.g. rolling a ball down an inclined plane Ideas about Earth Test 1 Study Guide Phys107, Quinn o No force is needed to keep the earth moving forward E.g. ball whirled on a string ▯ Isaac Newton (1642-1727) Newton’s First Law of Motion (Law of Inertia) – every object continues in its state of rest, or of uniform motion in a straight line, unless it is compelled to change that state by forces impressed upon it o Developed from Galileo’s concept of inertia o E.g. quickly pulling a tablecloth from under a dish An object continues doing whatever it is doing unless a force acts on it o E.g. resting a penny on a hoop over a bottle, then quickly removing the hoop so the penny returns to its state of rest, now inside the bottle ▯ Important Terms: Mechanics – the study of motion Net force – combination of all forces acting on an object Scalar – quantity with magnitude only Vectors – quantity with magnitude and direction; force is a vector quantity; vector sums take magnitude and direction into account when determining the net force Velocity – quantity of speed and direction Gravity & support force – quantities that are equal when an object is at rest; support force is created by atoms (negatively charged electrons) which repel each other because they’re moving so fast and are electrically charged Mechanical equilibrium – when the combination of forces acting on an object equals zero; if an object is moving at a constant speed in a constant direction, it is in mechanical equilibrium; mechanical equilibrium minus net force equals zero 2 Newton – (same unit as.. kg*m/s ) unit of force; e.g. 10N of force is pushing from the left side of a box, while 5N of force is pushing from the right side, so the box will move to the right with 5N of force Test Questions… 1. A worker with a weight of 1700 N stands on a 300 N platform suspended at rest by two ropes. The tension in the first rope is measured to be 600 N. What is the tension in the second rope? … (1400 N). Test 1 Study Guide Phys107, Quinn ▯ 1700 NEWTONS + 300 NEWTONS = 2000 NEWTONS ▯ = WEIGHT OF MAN AND PLATFORM 2000 NEWTONS – 600 NEWTONS = 1400 NEWTONS = THE AMOUNT OF HANGING FORCE BY THE SECOND ROPE 2. What a book weighing 3 N is lying at rest on a table, the force that the table exerts on the book is… (a support force of 3 N.) o For every action, there is an equal and opposite reaction. The book pushes on the table downward. The table pushes the book upward with the same exact amount of force, because it’s at rest. ▯ ▯ 3. If two 5 pound forces pull on an object, the magnitude of the net force is…(trick question! We need to know the direction in order to solve this problem.) ▯ 4. If you toss a coin straight upward in a train that gains speed while the coin is in the air, the coin will land… (behind you.) o If you toss a coin straight upward in a train that continues at a constant velocity, however, the coin will land as if you were at rest. ▯ ▯ 5. An object is in mechanical equilibrium if the net force on it is…(zero.) CHAPTER 3: LINEAR MOTION Basic Concepts of Linear Motion: Test 1 Study Guide Phys107, Quinn Speed – how “fast”/”slow” an object moves; scalar quantity; measured in (mi/hr), (m/s), (km/hr) for example SPEED = DISTANCE / TIME o Instantaneous speed – speed at a given instant; reading your speedometer in your car o Average speed – AVERAGE SPEED = TOTAL DISTANCE COVERED / TOTAL TRAVEL TIME Velocity – speed and direction an object is moving in; vector quantity Constant Velocity – motion in a straight line at a constant speed Changing Velocity – if speed and/or direction are changed, then velocity changes; this is the same thing as acceleration ▯ Acceleration – rate of change of velocity; how quickly/slowly velocity changes; includes a direction as well, but positive acceleration doesn’t necessarily mean speeding up, and negative acceleration doesn’t always mean slowing down; +/- indicates direction; measured in (mi/hr * s) for example ACCELERATION = (FINAL VELOCITY – INITIAL VELOCITY) / TIME E.g. steering, using the gas pedal, using the brake pedal in a car will all accelerate the car ▯ Vertical and Horizontal Motion – motion measured at 90 degree angles can be treated independently from one another ▯ ▯ Free Fall – an object is in free fall when gravity is the only force acting on it; in free fall, the acceleration of an object is 10m/s because that’s the force of gravity Velocity starting from rest with constant acceleration VELOCITY = ACCELERATION (gravity) x TIME o For example, 2 seconds after an object falls in free fall from being at rest, velocity is 20m/s; at 6 seconds, velocity is 60m/s Test 1 Study Guide Phys107, Quinn Velocity starting from an initial velocity with constant acceleration (an object thrown straight upward) FINAL VELOCITY = INITIAL VELOCITY + (ACCELERATION x TIME) o For example, throwing a ball straight upward where there is no air resistance: When the ball leaves the hand, it will have negative acceleration because it is accelerating in the upward direction at 10m/s 2 When the ball is traveling upwards toward its apex, there is a positive velocity that decreases over time 2 by 10m/s . When the ball reaches its apex, its velocity equals zero because – for a split second – the ball is travelling neither up nor down. Note: the acceleration is still equal to 10m/s at this point. When the ball falls back down, it has a negative velocity because it is travelling in the downward direction. The ball’s acceleration when it reaches the ground is the same acceleration as when it left the hand. Distance starting from rest with a constant acceleration: ▯ DISTANCE = (1/2) x ACCELERATION x TIME 2 ▯ Dropping a ball – Time Distance ▯ 0 sec 0 m ▯ 1 sec 5 m ▯ 2 sec 20 m 3 sec 45 m ▯ 4 sec 80 m ▯ (Every second, the ball is falling 10 meters faster than it was the second before it.) Test Questions… Test 1 Study Guide Phys107, Quinn 1. At one instant, an object in free fall is moving upward at 30 m/s. Five seconds later, its speed is about… (20m/s). Note that the object is moving upward. We know that acceleration in free fall, whether positive or negative in direction, is 10m/s .2 After one second, the speed is 20m/s; two seconds, 10m/s; three seconds, velocity = 0; four seconds (falling back down), 10m/s; five seconds, 20m/s 2. It takes 6 seconds for a stone to fall to the bottom of a mineshaft. How deep is that shaft? …(about 180 m). DISTANCE = (1/2) x (GRAVITY) x (TIME ) 2 ▯ (1/2) x (10 M/S ) x (6 SECONDS) = 180 METERS 3. If I drive 70 mi/hr from Memphis to Batesville for 1 hour, then drive 10 mi/hr through a construction zone for ½ hour, then drive 50 mi/hr from Batesville to Oxford for ½ hour, what was my average speed for the entire trip? …(50 mi/hr). ▯ AVERAGE SPEED = TOTAL DISTANCE COVERED / TOTAL TRAVEL TIME ▯ (70 MILES + 5 MILES + 25 MILES) / 2 HOURS = 50 MILES PER HOUR ▯ 4. A ball is tossed vertically upward. At it’s highest point, …(speed and velocity equal zero.) 5. While a car travels around a circular track at 90 km/h, its…(speed does not change.) Velocity and acceleration, however, do change, because direction is changing. Test 1 Study Guide Phys107, Quinn ▯ ▯ CHAPTER 4: NEWndN’S SECOND LAW OF MOTION ▯ Newton’s 2 Law of Motion – the acceleration of an object is… Directly proportional to the net force on an abject o If you double the net force on an object, its acceleration doubles; if you triple the net force, its acceleration triples In the same direction of the net force o If you push an object forward, it will accelerate forward Is inversely proportional to the mass of an object o If you double the mass of an object, its acceleration will be cut in half; if you triple its mass, its acceleration is 1/3 of what it originally was ▯ Difference between Mass and Weight Mass – (kg) the amount of matter in an object; the mass of an object does NOT change from location to location; the English unit for mass is stones/slugs, but these are rarely used o If you shake a light ball, it’s easy to move back and forth (horizontally); if you shake a heavy ball, it’s harder to move it back and forth o WHY? The more mass, the more inertia – which means the more mass, the more resistance to motion. Weight – (lbs., N) the force upon an object due to gravity o If you’re trying to differentiate the weight of 2 objects, you would hold an object in each hand and slowly move your hands vertically o WHY? We’re measuring the force of gravity 1 kg = 2.2 lbs 1 kg = 10 N 10 N = 2.2 lbs Test 1 Study Guide Phys107, Quinn 1 N = .22 lbs 1 lbs = 4.5 N The relationship between mass and weight: ▯ WEIGHT is proportional to MASS ▯ NEWTON = kg X (m/s ) 2 ▯ Friction – the force created when objects slide against one another; also occurs in liquids and gases (fluids) o Always in the opposite direction of the object’s motion o Reduces net force and, consequently, the acceleration of an object Types of friction: o Sliding friction – when you move something across a surface Before antilock brake systems in cars, if you slammed on the brakes, your tires would lock up and your tires would skid/slide across the concrete, which is NOT effective because we’d lose control o Static friction – when something is resting on/touching something else With antilock brake systems in cars, our rolling tires create static friction because only one point of the tire rests on the ground at any given moment; when we slam on our brakes, our wheels keep rolling, but it is more effective because there’s more friction and we do NOT slide/skid and lose control For SOLIDS, friction depends on: o The materials that are rubbing together o How hard they’re pressing against each other For SOLIDS, friction does NOT depend on: o Speed – no matter the speed of the two objects, the amount of friction is the same Test 1 Study Guide Phys107, Quinn o Surface area – no matter the surface area of the objects, the friction will be the same For FLUIDS, friction depends on: o Speed – because of air resistance o Surface area – for example, you can canoe faster than you can propel a barge ▯ ▯ ▯ ▯ Free Fall – remember, the only force acting on an object in free fall is gravity, not air or anything else Everything falls at the same rate in free fall, no matter the size or weight If weight is doubled, so is the mass, so they cancel each other out and always equal 10m/s 2 ▯ NET FORCE = GRAVITY = WEIGHT ▯ ACCELERATION = WEIGHT/MASS ▯ GRAVITY = WEIGHT/MASS ▯ WEIGHT = MASS x GRAVITY 2 ▯ GRAVITY = 10m/s ▯ Non-Free Fall – when objects are falling in the presence of air Air resistance reduces acceleration if it’s moving downward ▯ NET FORCE = WEIGHT – AIR RESISTANCE ▯ RESISTANCE / MASS = ACCELERATION DUE TO GRAVITY ▯ ACCELERATION = (WEIGHT / MASS) – (RESISTANCE / MASS) ▯ ACCLERATION = GRAVITY – (RESISTANCE / MASS) Test 1 Study Guide Phys107, Quinn For example, someone is dropping a plastic ball and a steel ball of the same size from the top of 2 story building o Right as they’re dropped, the two balls have the same acceleration and have a velocity of zero o While the plastic ball falls through the air, the net force on the on it is reduced as air resistance (air drag) builds up, which causes the acceleration to decrease. o The steel ball has a larger force of gravity, so air drag does not affect it as much, allowing its acceleration to increase Terminal Speed – the speed at which the acceleration of a falling object terminates because air resistance balances gravitational force; when the air resistance is as large as the weight of the object, so it no longer accelerates Terminal Velocity – when an object reaches terminal speed in a specified direction Forces on an object: ____|Z|____ (*FYI: This is a box on the ground and the possible forces on the object*) o Box is sitting still – all forces are equal to zero o A truck pulls the box at a constant 1 mile per hour to the left – all forces STILL equal zero WHY? If an object is moving at a constant velocity, then the pushing/pulling force must be exactly equal to friction (the opposing force), which means they cancel each other out. The zero net force then results in zero acceleration and constant velocity. o A truck pulls the box at an accelerating rate to the left – we don’t know the friction because the force is changing Test Questions… 1. If you double the net force on an object, you’ll double its… (acceleration.) Test 1 Study Guide Phys107, Quinn FORCE = MASS x ACCELERATION 2. Nellie accelerates a wagon at 4 m/s by pulling on it with a constant horizontal force of 160 N. If there are no other horizontal forces, what is the mass of the wagon? …(40-kg). FORCE = MASS x ACCELERATION 160 N = MASS x 4 M/S 2 3. If one object has three times as much weight as another object, it also must have three times as much…(trick question…different weights do NOT affect mass, inertia, or acceleration!) 4. A rocket becomes progressively easier to accelerate as it travels upward from the ground mainly because…(the mass of the rocket decreases as fuel is burned.) 5. The mass of a lamb that weighs 110 N is about…(11 kg). 1 KILOGRAM = 10 NEWTONS 11 KILOGRAMS = 110 NEWTONS Test 1 Study Guide Phys107, Quinn CHAPTER 5: NEWTON’S THIRD LAW OF MOTION Newton’s 3 rdLaw of Motion – whenever one object exerts a force on a second object, the second object exerts and equal and opposite force on the first; with every action, there is an equal and opposite reaction All forces come in pairs o For example, hitting a nail with a hammer: the nail digs downward into the wood, while your hammer bounces back upward o Driving a car down the road: the tires push the road backward, while the road pushes the tires forward o Round trip flight from NY to LA: the trip from NY to LA is equal and opposite to the flight from LA back to NY Action and Reaction on Different Masses – A good way to think about this is with the size of planets: These two planets are vastly different in size, but their action/reaction forces are exactly equal, as stated in Newton’s Third Law. However, the leftward acceleration force would be greater felt by the planet with the smaller mass. The larger planet would also accelerate to the right, however, due to the difference in their masses, the acceleration of the large planet may be undetectable. FORCE / MASS = ACCELERATION FORCE / MASS = ACCELERATION Action/Reaction Systems – So if an action has an equal and opposite reaction, why don’t the forces cancel each other out? Think of it as a system – there are at least two objects in play.. if one person pushes their hand against a wall, the hand and the wall are a system. The forces are being applied to different objects! Test questions… 1. A 400-kg bear grasping a vertical tree slides down at constant velocity. The friction force between the tree and the bear is…(4000 N). 2 NEWTON = kg * (m/s ) = WEIGHT(force) = MASS * GRAVITY Test 1 Study Guide Phys107, Quinn Friction is an equal and opposite force to the bear’s weight, and since he is sliding at a constant velocity, those forces cancel each other out. His acceleration, due to constant velocity, is zero, because acceleration is velocity that is CHANGING. 2 (400-KG) * (10m/s ) = WEIGHT and FRICTION FORCES 2. Two factors that greatly affect air resistance on falling objects are…(the size and speed of the object.) The greater the size of the falling object, the greater the amount of air resistance the object will encounter. This is due to the larger amount of surface area on the object that air particles act upon as the object travels. As a falling object accelerates downward through air, it's speed and air resistance increases. While gravity pulls the object down, we find that air resistance is trying to limit the objects speed. Air resistance reduces the acceleration of a falling object. 2 3. How much pushing force is needed to accelerate a 60-kg desk at 1 m/s across the floor if the friction force is 80 N? …(140 N). Remember, you must first overcome the friction force when accelerating an object. Fnet(pushing force – friction force) = MASS x ACCELERATION PUSHING FORCE – 80 N (friction force) = 60-KG x 1-M/S 2 Test 1 Study Guide Phys107, Quinn Remember, kg x (m/s ) = N, so… PUSHING FORCE – 80N = 60 N PUSHING FORCE = 140 N 4. A falling skydiver of mass 100-kg experiences 700 N of air resistance. The acceleration of the skydiver is…(0.3 g). There are two forces acting on the skydiver....one force is explicitly stated (air resistance), and the other is implied (the sky diver's weight). The force of gravity on the skydiver is his weight. MASS x GRAV2TY = WEIGHT 100 KILOGRAMS x 10 M/S = 1000 NEWTONS downward Air resistance is 700 N upward. If there were no air resistance, the net force would be 1000 N and his acceleration would be g. But since the net force on him with air resistance is now 300 N downward... 300 NEWTONS / 1000 NEWTONS = .3 (gravity) 5. A skydiver steps from a helicopter and falls for a few seconds until terminal velocity is reached. Thereafter, until he opens his parachute, his acceleration…(is zero.) If he has reached terminal velocity, that means his velocity is zero against the air resistance. When velocity is zero, acceleration must be zero also, since acceleration is the rate velocity changes.
Are you sure you want to buy this material for
You're already Subscribed!
Looks like you've already subscribed to StudySoup, you won't need to purchase another subscription to get this material. To access this material simply click 'View Full Document'