80 terms

physics exam

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What is science?
systematic study of the physical world through observation and experiment
What 3 things must be true to a statement to be scientific?
1. falsifiable
2. unbiased
3. reproducible
"unscientific" vs. "scientific" statements
"unscientific" statements cannot be proven with research and experimentation but "scientific" statements can be
qualitative measurement
measurements using characteristics
quantitative measurement
measurements using numbers and units
What is the scientific method?
way to ask and answer scientific questions by making observations and doing experiments
What was our hypothesis for Lab 1?
We think that based on a student's experience, the green Dawn Ultra is very bubbly and will produce the best bubbles.
What was our conclusions for Lab 1?
Our original hypothesis cannot be supported because the data was inclusive which shows that not one particular soap brand was better than the other. In the future, we can work to create better bubbles by using a different ratio of soap to water plus experimenting with various amounts of baking soda and using the same person to produce the bubbles in order to form a more reliable dataset.
two types of Aristotelian motion
natural motion and violent motion
example of natural motion
smoke
example of violent motion
boat being pushed by wind
What is "natural state"?
way you find something without it being touched
natural state of smoke
air pushing up
natural state of moon
rotating around the Earth or being held in space
natural state of rock
pushing down on Earth
What was special about Galileo's methods over previous dissenters of Aristotle?
Galileo's methods were proven through observation and experiment and was the first to do so.
two of Galileo's experiments we discussed?
1. Leaning Tower of Pisa
2. rolling objects across inclined planes
major conclusions of Galileo's experiment
different objects fall at same rate and discovered inertia
How do Galileo's experiments refute a previous idea set out by Aristotle?
Aristotle said that the more massive object would fall faster and that all objects want to stay at rest whereas Galileo proved that objects want to fall at the same rate unless air resistance and that all objects want to stay moving or stationary.
Newton's First Law
His first law states that every object continues in a state of rest or of uniform speed unless acted upon by a non-zero net force.
Inertia
Inertia is the property of all mass in which it resists change in motion
Inertia vs. Weight Demo
When string is pulled quickly, the lower string will break because of inertia, and if the string is pulled slowly, weight will cause the top string to break.
Why can't you travel via helicopter to the State of Liberty by hovering and letting the Earth spin underneath you?
It is because everything is moving at a constant speed.
Force
A force is a push or pull in a direction.
SI and imperial units of force
SI unit is newton (N) and imperial unit is pounds (lbs)
Net Force
The sum of all forces on an object.
What is a vector?
A quantity that has both magnitude and direction
example of a vector
force
What is a scalar?
A scalar is a quantity or measurement that just has magnitude and no direction.
example of a scalar
temperature
vectors that are parallel to each other
use arrows going to the left (negative) and/or right (positive) to help with adding vectors
vectors that are not parallel to each other
"parallelogram rule" : draw both vectors on opposite sides (preserve length and angle); the diagonal of the parallelogram is the sum of the vectors also known as the resultant vector
vectors at right angles
use pythagorean theorem
break any vector into "x" and "y" components
use "parallelogram rule" backwards
Support Force
It is the upward force perpendicular to surface of contact
When is support force not "upward"?
When you push on a wall or if it is on a slope.
Which rope has more tension in a two-rope hanging problem?
There is more tension on the shorter side of the rope.
Speed
How fast an object moves. (speed=distance/time)
average speed equation
average speed= total distance/total time
What is the difference between speed and velocity?
Velocity has a direction because it is a vector whereas speed is only a scalar.
example of units of speed or velocity
meter per second
two possible interpretations for a velocity of -20 mph
decelerating or going backwards
Instantaneous Velocity and Average Velocity
Instantaneous velocity is speed at any given instant, and average velocity is speed at given period time
Acceleration
It is change in velocity.
acceleration equation
acceleration= change in velocity/ change in time
Is acceleration a vector?
Yes.
two example of when "accelerate" doesn't mean "speed up"
when car stops and when car turns on a street
equation for acceleration if given two velocities and a time interval
acceleration= final velocity-initial velocity/ final time-initial time
What is free fall?
It is when an object is under influence of gravity alone and there is no air resistance.
value of "g"
10 m/s^2
What does "g" mean?
"g" means gravity.
During Lab 2, what value did you calculate?
We calculated for 9.81 m/s^2 which is acceleration due to gravity.
Why could this value be different from the standard value given in your textbook?
It could be different because when we measured the teeth marks with a ruler, it could have been not accurate. (?)
instantaneous velocity equation of an object in free fall
instantaneous velocity= acceleration x time
equation to calculate how far an object has fallen in free fall or to calculate hang time
distance traveled= 1/2 (g) (t^2)
Why was the final time, t, doubled to give the total hang time?
It was doubled because the total hang time consisted of the time going up and then going back down.
What is the distance an object in free fall travels in 1 second?
5 m/s
Can an object have zero velocity, but have a non-zero acceleration? Explain.
Yes for instance, if you throw a ball in the air and when the ball stops in the middle of the air, the object has zero velocity but has a non-zero acceleration because the ball changes acceleration when it stops.
If an object is thrown down with an initial velocity, will this affect the acceleration 1 second later?
The acceleration will remain the same but the ball will be traveling due to not falling from rest.
Friction
A force that opposes the direction of motion.
Is the amount of force different on inclined surfaces of different angles?
Yes. There is less friction on more incline planes and more friction on less inclined planes.
Is there a difference between static friction and kinetic friction?
Yes. Static friction has a greater force than the kinetic force.
Does friction depend on the speed of the moving object?
Yes. The friction was less when we moved the object faster and the friction was more when we moved the object slower.
Does friction depend on the size of the area of contact between the two objects?
No.
What is kinetic friction? Static friction? Compare the two.
Kinetic friction also known as sliding friction is when an object slides across a surface whereas static friction is the build up before it slides. Static friction is greater than kinetic friction.
What is the net force on an object traveling at a constant velocity?
The net force is 0.
Does a net force of zero mean that no forces are acting on an object. Explain and give an example.
It means that the forces cancel out. If you push against someone else there is a net force of zero but there is still force being applied.
Mass
Mass is the amount of stuff. It is the measure of resistance to motion.
SI units of mass
kilograms
Weight
Weight is the force of gravity.
SI units of weight
newtons
Newton's Second Law
Newton's 2nd law is that a force is the acceleration of a mass. That acceleration is in the same direction as the net force.
equation to calculate weight for any object if given the mass
F=ma
Be able to convert Newtons to pounds if given a conversion factor.
example: 4N=2lbs->divide each side by 4
What is non-free fall?
Non-free fall is when air resistance is not ignored.
What is terminal velocity?
Terminal velocity is the maximum speed that a falling object reaches.
What is Newton's 3rd Law? Give two definitions.
1. "For every action there is an equal and opposite reaction"
2. When an object exerts a force on the second object, the second object exerts a force back equal in magnitude but in the opposite direction.
What is an "action-reaction" pair?
An "action-reaction" pair is when there is equal force in opposite directions.
How can the force of gravity on your body be equal (but opposite) to your force on the earth? Explain.
The force of gravity is equal in magnitude but in the opposite direction. F1=F2
Explain why a gun recoils after firing a bullet.
It is because when a gun fires a bullet, it exerts force forward, but then the bullet exerts equal force backwards making the gun recoil. Ma=Am