Physics Exam One (chapters 1-5)
Terms in this set (53)
What is science?
-Science is a way of knowing about the world and the universe
-Science relies on data: information gathered by the 5 sense
-Data must be measurable to be important in science
The Scientific Method
-Observation, hypothesis, prediction cycle
-The process can begin at any point and continue forever
-Possible explanation, a small theory
-Something taken to be true for the purpose of argument or investigation
-Not just a random guess
-Observe facts, things that can be measured usually within numbers
-To gather data: experiment, control variables, changing some and keeping some constant and measure the results
-Are not immutable and absolute but are generally in close agreement as measured by competent observers of the same phenomena
-MUST be testable
Test the Hypothesis
-Examine the data or observation carefully looking for patterns
-Synthesis of a large body of information that encompasses well tested and verifiable hypotheses to explain how the natural world works
-Gravitation, Atomic Theory, Cell Theory
-Theories are always subject to challenge and change
-Refined as new evidence (which is a strength not a weakness
-Must be testable, must be continually tested, should be simple and should be elegent
Fact vs Theory
-Theories are not facts
-Facts can be measured
- Theories explain the measured facts
Laws vs Theory
-Law is a statement about relationships
-Theory is the best possible explanation about why the law exists
Honesty in Science
-Honesty in science is matter of public and self interest
-Misrepresent or fudges data or caught lying about scientific information is ostracized by the scientific community
The science concerned with the discovery and understanding of the fundamental laws which govern matter, energy, space and time
The property of things to resist change in motion
What is Newton's First Law of Motion
Every object continues at a state of rest or uniform or speed in a straight line, unless acted on by non zero net force.
a push or a pull SCIENTIFIC UNIT= N. / US unit =lbs
Is the (VECTOR) summative action of all external forces acting on an object.
Copernicus started a scientific revolution that the planets revolved around the sun.
What is the difference between Copernicus/Galileo and Aristotle's theory about the earth's rotation?
Aristotle: believed in a geocentric Universe and that the planets and stars were perfect spheres though Earth itself was not. He further thought that the movements of the planets and stars must be circular since they were perfect and if the motions were circular, then they could go on forever.
Copernicus: His heliocentric system put the Sun (helio) at the center of our system. He was not the first to have this theory. Earlier star-watchers had believed the same, but it was Copernicus who brought it to the world of the Renaissance and used his own observations of the movements of the planets to back up his idea. His ideas, including the revelation that the Earth rotates on its axis, were too different for most of the scholars of his time to accept. They used only parts of his theory. Those who did study his work intact often did so in secret. They were called Copernicans.
Galileo: He had his own ideas on how motion really worked, as opposed to what Aristotle had taught, and devised a telescope that could enlarge objects up to 20 times. He was able to use this telescope to prove the truth of the Copernican system of heliocentrism. He published his observations which went against the established teaching of the Church. He was brought to trial and, although he made a confession of wrong-doing, he was still kept under house arrest for the rest of his life
What relationship between the sun and the earth did Copernicus formulate?
The Earth revolves around the Sun
What is the net force on a cart that is pulled to the right with 100 lbs and to the left 30 lbs?
70 lb to the right
When you stand at rest on a bathroom scale how does your weight compare with the support force by the scale?
A force of gravity pulls downward on a book that's on the table. What force prevents the book from accelerating downward.
-A description of how fast
Speed at any instant
total distance covered/time interval
-the speed and direction of an object
- constant speed and constant velocity
-A curved track may have constant speed, but because its direction is changing, its velocity is not constant.
-Change in velocity/time interval
-Acceleration is not just the total change in velocity; it is the time rate of change, or the change per second in velocity
-Units for acceleration is m/s*s or m/s^2
-We accelerate when we move in a curved path even when we move in a curved path because the direction is changing, our velocity is changing.
-The term acceleration refers to deceleration as well as increases in velocity.
Acceleration on Inclined Planes
-Velocity= acceleration X time
-Galileo found that a ball rolling down an inclined plane picks up the same amount of speed in successive seconds; that is, the ball rolls with unchanging acceleration
-things fall because of the force of gravity
-During each second of fall the object gains the speed of ten meters/second
-Free fall acceleration is approximately equal to 10m/second each second. (Time is entered twice; once for the unit of speed and again for the time interval in which the time changes.)
-g=acceleration (because the acceleration is due to gravity) true value is 9.8m/s^2
acceleration X time (v=gt)
1/2 (acceleration X time X time) or d=1/2gt^2
You are driving north on a hwy and without changing speed your round a corner and go east.
a) Does your velocity change?
b) Do you accelerate?
a) Yes, because of the change of direction
b) Yes, because of the velocity changes
Cite an instance in which your speed could be zero while your acceleration is non-zero.
a vertically thrown ball has zero speed at the top of its trajectory, but acceleration there is g
If it were not for air resistance why would it be dangerous to go out on rainy days.
If it were not for the slowing effect of the air, raindrops would strike the ground of high speed bullets
Newton's Second Law of Motion
-Force produces acceleration. F=ma
-Acceleration depends on the net force. To increase the acceleration of an object, you must increase the net force acting on it.
-An object's acceleration is directly proportional to the net force acting on it:
acceleration ~ net force
-The relationship between acceleration, force and mass
· "The acceleration of an object is directly proportional to the net force acting on the object, is in the direction of the net force, and is inversely proportional to the mass of the object.
· Acceleration ~ net force/ mass
*an equal sign can be used if the same unit of measurement is used throughout
· A = Fnet/m
The direction of the friction force is always in a direction opposing motion.
· The friction of sliding is somewhat less than the friction that builds up before sliding takes place. These forces are known as sliding friction and static friction.
· ? The force of static and sliding friction do not depend on speed. These frictions also do not depend on the area of contact.
· Fluid friction occurs in liquids and gases as an object pushes aside the fluid it is moving through. Fluid friction does depend on speed.
· Air resistance is a type of fluid friction, also known as drag.
Once a crate is sliding, how hard do you push to keep it moving at a constant velocity?
the force you need to exert would have to equal the opposing force of friction
Mass and Weight
Mass is neither weight nor volume.
· The acceleration imparted to an object depends not only on applied forces and friction forces, but on the inertia of the object.
· Mass is the quantity of matter in an object, and a measure of the inertia of a material object.
· Weight is the force upon an object due to gravity. W=mg
· Mass Resists Acceleration (inertia)
· For a given force, the acceleration produced is inversely proportional to the mass.
acceleration ~ 1/mass
· 1 kilogram is approximately 2.2 pounds here on Earth.
· A kilogram measures the mass of an object.
· Newtons measure force.
· 1 Newton is a little less than a quarter-pound, or approximately .22lb - about the weight of an apple.
· 1 kilogram brick weighs about 10 newtons (or precisely 9.8N)
· *the units N/kg are equivalent to m/s^2 when referring to the acceleration of gravity
· the metric system will express quantities of matter in units of mass (grams or kilograms) and not in our customary measure of weight (newtons, or pounds) which are both measures of a force (gravity).
Is acceleration directly proportional to mass, or is it inversely proportional to mass? Give an example.
Acceleration is inversely proportional to mass. Increasing mass means decreasing acceleration, for example
How does the direction of acceleration compare with the direction of the net force that produces it?
acceleration and net force are in the same direction
When Acceleration is g - Free Fall
-g = f/m
f means weight (WHY USE F THEN?)
g means acceleration, and we use g to express that the acceleration is due to gravity alone.
-The greater the mass of an object, the greater is the gravitational force of attraction between it and the Earth.
-Ponder this --> The acceleration of an object depends not only on the force - in this case, the weight - but also on the object's resistance to motion, its inertia. Force causes acceleration, but inertia is a resistance to acceleration.
-The ratio of weight to mass for freely falling objects equaling a constant g, is similar the constant ratio of circumference to diameter for circles, which equals the constant pi.
Why doesn't a heavy object accelerate more than a light object when both are freely falling?
Because the greater mass offsets the equally greater force; whereas force tends to accelerate things, mass tends to resist acceleration.
A = F/M = 2F/2M
When acceleration is less than g - non free fall
-In non free fall, the f of the equation is the net forces acting on an object, air resistance and gravity, as opposed to just gravity (or its weight) alone.
-In the presence of air resistance, the net force is less than the weight - it is the weight minus air drag.
-here, a = mg - R / m, where mg is the weight and R is the air resistance.
-The force of air drag experienced by a falling object depends on two things: the size and the speed of a falling object.
-the frontal area of the falling object - that is, on the amount of air the object must plow through as it falls.
-the speed of the falling object; the greater the speed, the greater the number of air molecules an object encounters per second and the greater the impact.
-When acceleration terminates, the object has reached its terminal speed/velocity.
What is the acceleration of a falling object that has reached its terminal velocity?
When an object reaches its terminal velocity, it can no longer accelerate, so its acceleration becomes zero, and it falls at a constant speed. As an object falls freely through the air, it has two forces acting upon it: gravity and drag.
a quantity that requires magnitude and direction
a quantity that requires only magnitude
the sum of two or more vectors
mutually perpendicular vectors, usually horizontal and vertical, whose vectors sum is given vectors
defines which mass is being acted on
Action and Reaction on Different Masses
The forces are equal, the acceleration is determined by the amount of mass of the objects. The greater the mass the smaller the acceleration.
If you drop a rubber ball on the floor, it bounces back up. What force acts on the ball to provide the bounce?
When the ball exerts a force on the floor, the floor exerts an equal and opposite force on the ball- hence bouncing .The force on the ball provides the bounce.
Why can you exert greater force on the pedals of a bicycle if you pull up on the handle bars?
When you pull up on the handle bars the handle bars simultaneously pulled down on you, it's downward force is transmitted to the pedals.
-The state of an object or system of objects for which any impressed forces cancel to zero and no acceleration occurs.
• Support Force = Weight (but in opposite directions)
• Doesn't mean that velocity = 0; but rather that the object will maintain the velocity it happens to have
• Ex. if a book that weighs 15N is at rest on a table, the table must be pushing back with 15N of support (normal) force, in order for there to be no acceleration.