Midterm I Flashcards
(76 cards)
1
Q
Define Classical Mechanics
A
The study of slow motion of macroscopic objects.
2
Q
What is involved in Classical Mechanics?
A
Kinematics-Dynamics-Conserved Properties
3
Q
What is the significance of Kinematics?
A
It describes HOW things move.
4
Q
What is the significance of Dynamics?
A
It explains why things move.
5
Q
What is included in Conserved Properties?
A
Momentum, Energy
6
Q
What are the base units for common quantities (SI)?
A
Kg for Mass; Meters for Length; Seconds for Time
7
Q
What are the units for a Watt?
A
1 kg.m^2/s^3
8
Q
To convert from one system to another, we use a _____.
A
Conversion Factor
9
Q
What are the rules for significant figures when it comes to addition/subtraction and multiplication/division respectively?
A
With addition and subtraction, you round it to the least precise measurement. With multiplication and division, you round it to the # w the least amount of significant figures.
10
Q
Define Motion
A
Change in object’s position with time.
11
Q
What do equal, increasing, and decreasing distances between each time in motion diagrams tell us about the object?
A
Equal Distance: constant speed.
Increasing Distance: speeding up.
Decreasing Distance: speeding down.
12
Q
How do we represent objects in motion diagrams?
A
As a single dot (all mass concentrated at 1 point).
13
Q
How is the origin of a coordinate system determined
A
It is up to the individual.
14
Q
What is another way to describe the magnitude of a vector?
A
The length of a vector.
15
Q
Define Dispacement
A
The change in position between 2 time intervals.
16
Q
Is displacement a scalar or a vector?
A
Vector (has a magnitude and a direction)
17
Q
What is the way to calculate displacement?
A
Later Position- Initial Position
18
Q
What do scalars have?
A
Only a numerical value.
19
Q
What do vectors have?
A
A quantity and a direction
20
Q
Define Velocity
A
The ratio of the displacement vector divided by the time interval of displacement.
21
Q
Where does the velocity vector point?
A
In the SAME direction as the displacement vector.
22
Q
Define Acceleration
A
Change in velocity. It is calculated by calculating the change in velocity over the time interval.
23
Q
How do we figure out a change in velocity when given 2 vectors?
A
You do V2-V1 ; (V1 being of the same magnitude but in the opposite direction)
24
Q
What can be said about the acceleration due to gravity?
A
Always down and has the same magnitude.
25
What are the two components of a vector (geometrically)?
The head and the tail (head being the arrow).
26
How do you do vector addition?
Place the head of one vector at the tail of another; THEN, connect LOOSE TAIL to loose head.
27
How do you do vector subtraction?
Subtracting is the same thing as adding a negative. (Same rules apply for addition, direction is opposite for negative vector).
28
How can you determine whether a vector is positive or negative?
It is positive if it points in the positive direction (towards LARGER POSITIVE NUMBERS)
29
What does a position graph tell us?
Determines the time and position of each point in the diagram as a function of position vs. time (time on x axis and position on y-axis).
30
How does a constant velocity look like in a position vs time graph?
It results in a straight line. (Slope= (xf-xi)/(tf-ti))
31
What is the equation for finding final position based off constant velocity graph?
Xf= Xi+VxΔt (xf is final position; Vx= velocity (which is constant) ; xi= initial position))
32
How do you calculate the instantaneous velocity in a problem?
It is the derivative of the position vs. time graph at time t.
33
How are position, velocity, and acceleration related to one another in calculus terms?
Velocity is the derivative of position and acceleration is the derivative of velocity.
34
If velocity is constant, how do you find the change in position from velocity graph?
Δx=VxΔt
35
How do you find position from velocity graph if the velocity is NOT CONSTANT?
Xf= Xi + Integral Of Vx (with final time being the upper bound and the initial time being the lower bound)
36
What can be said about the acceleration of a velocity v. time function that is linear (same slope)?
The acceleration would be constant.
37
If acceleration is constant, ______ becomes a function of _____. What is the equation for that?
V-T; Vf= Vi+AΔt
38
If acceleration is positive, what can be said about the position function graph? What about if acceleration is negative?
Positive—-> position function is concave up.
Negative—-> position function is concave down.
39
What is something important to note about the following equation? (Vf^2=Vi^2+2aΔx)
You have to be careful when solving for v. Because V is squared, it loses its sign.
40
Near the surface of the Earth, do all objects in free fall accelerate downward at the same rate?
This is ONLY true if air resistance is very small. A good assumption if objects are not heavy, traveling not too fast, or are aerodynamic.
41
What is the value for acceleration?
-9.8m/s^2
42
What are the things to keep in mind when. Using the kinematic equations of motion?
Identify the initial and final parts of the equation.
Define a coordinate system (origin and positive directions)
List all known quantities.
Determine what you want to solve for
If there is an equation where the only thing you want to solve for is the unknown, use it; if there’s 2 unknowns, use two equations.
43
When trying to solve for “t” using the first kinematic equation (one that involves 1/2a(Δt)^2), how do you go about it?
You must use the quadratic formula. First, arrange the equation accordingly: at^2+bt+c=0 —-> arrange in a way where exponents of “t” are in a descending order.
“C” has no exponent; “b” has 2nd highest power; “a” has highest power.
44
Is vertical acceleration affected by horizontal motion (in the case that motions are perpendicular)?
No.
45
Perpendicular motions are _____. Explain.
Independent. They don’t affect one another.
46
Define Projectile Motion
Objects falling due to gravity, but also moving horizontally. (NO ACCELERATION IN THE X-DIRECTION)
47
How is motion in the horizontal direction characterized in projectile motion?
It is uniform (constant velocity)—-> ACCELERATION is 0.
48
When decomposing vectors into perpendicular components, how do you determine (vy)0 and (vx)0?
(Vx)0= vicos(theta)
(Vy)0=visin(theta)
49
What are the sines and cosines of 30,45, and 60 degrees respectively?
30: sine is 1/2, cosine is root 3 over 2.
45: both are root 2 over 2
60: cosine is 1/2, sine is root 3 over 2.
50
With projectile motion, what is how long something in the air for dependent upon?
SOLELY on the y-component.
51
What is the convention when drawing forces?
Drawn with the tail of the vector on the object feeling the force.
52
Forces are either a _____ or a _____ action.
Pushing/Pulling
53
What are examples of pulling force?
Tension in ropes, springs.
54
What are examples of pushing forces?
Pushes, shoves, and collisions.
55
What is Newton’s First Law?
An object with no forces on it and at rest, will stay at rest. An object with no forces on it that is moving will continue to MOVE IN A STRAIGHT LINE AT A CONSTANT SPEED. (If it’s already in motion, it does not require additional force to continue to move).
56
What is Newton’s Second Law?
An object of mass M subjected to forces F1, F2, F3, … will undergo acceleration given by a= F Net/m where F net isthe sum of all the forces acting on the object. The acceleration vector a points in the same direction as F net.
57
Where does the acceleration vector point with respect to the F Net?
In the same direction.
58
What is the equation for F Net?
F Net= ma where m is in kg, a is in m/s^2.
The units of force are (kg.m)/s^2 denoted by N (newtons)
59
Explain everything important about gravitational force.
Always pointing down towards the center of the earth; magnitude is dependent on mass. DENOTED by “w”
60
Explain everything about Spring force.
Pushes if spring is compressed. Pulls if spring is stretched. Magnitude of force increases with increased stretch or compression. DENOTED by Fsp.
61
Explain everything important about Tension force.
Force is always in the direction of the rope. Rope can pull, not PUSH. Denoted by “T”
62
Explain everything about normal force.
Always perpendicular to the surface. Denoted by “n”
63
Explain everything important about friction forces.
Always opposes the motion, always parallel to the surface. Kinetic friction is the force when surfaces are slipping elective to one another and Static friction is the force when surfaces DON’T move relative to one another.
64
Explain everything about Drag Force.
Always opposes the direction of motion. Dependent on the and speed of object and the density of gas/liquid.
FORCE you feel when you are moving through some medium (gas/liquid).
65
Explain everything important about Thrust Force.
A force created by expelling gases at high velocity. FORCE is in opposite direction of expelled velocity. Denoted by F Thrust.
66
What are electromagnetic forces?
Force without touching.
67
What are the steps involved in drawing a free-body diagram?
1) identify all the forces acting on the object
2) develop a coordinate system
3) represent object as dot
4) draw vectors representing each of the identified forces.
5) draw and label net force vector to the side of the diagram.
68
In the situation where an elevator is accelerating downwards from the top floor, how do the forces compare?
The magnitude of the weight force is greater than the Tension of the rope, allowing for the elevator to move DOWN.
69
An elevator is moving up at a CONSTANT velocity. How do the forces compare? Why?
The tension and weight forces are completely equal I’m magnitude and opposite in direction. This is the case because we mentioned that the acceleration is CONSTANT, implying that the velocity is constant as well.
70
What is the formula for w?
W= mg (mass and weight are directly proportional)
71
What is the difference between mass and weight?
Mass is how resistant an object is to acceleration when a force is applied to it.
Weight is the force of gravity pulling down on the object. (Dependent on how big plant is and how far you are from the center of the planet).
72
Let’s assume someone is in an elevator with a scale under them. If the elevator is accelerating upward, how are the forces compared to one another and what would the scale show?
Since there is acceleration upward, normal force is greater than weight. In this case, APPARENT WEIGHT is greater than true weight.
73
Let’s assume someone is in an elevator with a scale under them. If the elevator is not accelerating, how are the forces compared to one another and what would the scale show?
Since there is no acceleration, the magnitude of the normal and weight forces are exactly the same. Thus, apparent weight is true weight.
74
Let’s assume someone is in an elevator with a scale under them. If the elevator is accelerating downward, how are the forces compared to one another and what would the scale show?
Since there is acceleration downward, the weight force is greater than the magnitude of the normal force. Thus, apparent weight would be LESS than actual weight.
75
What is something essential to do when dealing with free-body diagrams?
1) draw the force diagram.
2) write equations of force for each component (forces in the X direction and forces in the Y-direction).
76
How can you tell if an object turned around by looking at a graph?
You must take a look at the position graph. The time where it starts changing its progression is the time where the object turns around. (For example, let’s say from 0-4 sec, the position was negative; then, at 4 sec, it starts progressing upwards —> that’s when the object turns around).
