Chapter 2 Flashcards
Motion
A very important topic to physics. Can be represented by a series of pictures. Or a series of dots.
Kinematics
How things move: the relationships among distance, time, speed, acceleration, ect.
Dynamics
What causes things to move and how much: force, impulse, momentum, ect.
What does it mean if the dots are evenly spaced?
That means the object is moving at a steady speed.
What does it mean if the dots are getting further a part?
The object is speeding up and if the dots are getting closer together the object is slowing down.
Distance
How far the object is from a certain point (or how far it goes to get there). Magnitude only. Standard unit of measurments is meters.
Position
Where an object is. It requires a reference point. Both magnitude and direction. Standard unit of measurments is meters. [Direction in Square Brackets]
Scalar
Is a quantity that has magnitude only. - distance, speed, height, time, mass, energy. Represented by just a letter.
Vector
Is a quantity that has magnitude and direction. - force, velocity, position, displacement, acceleration. Represented by a letter with a right-pointing arrow on top.
Combining scalar quantities:
Dt = D1 + D2
Combining vector with matching direction:
–> –> ->
Dr = D1 + D2
Magnitues simply add together algerbraically
Component vectors
When two vector quantites are combined to prodcue a new vector.
Resultant vector
Sum of two vector
Scale drawing solution or “Tip to tail” method - Same direction
Method of adding vector. You draw the first vector(and label it), then draw the second vector with it’s tail at the tip of the fist vector. The resultant vector is then draw with it’s tail at the tail of the first vector and it’s tip at the tip of the second component.
Vectors with opposite directions:
You can’t add two vector quantaties if they don’t have matching directions. Solution is to change the way one is expressed so that the directions match.
–> –> –>
Dr = D1 + D2
–>
Dr = ?
–>
D1 = 5m[E]
–>
D2 = 3m[W] : –> -3m[E]
–>
Dr = 5m[E] + (-3m[E])
= 2m[E]
Scale drawing solution - Opposite directions
As long as motion is just a straight line so that the directions of the component vectors are the same or opposite, it is easy to draw. Just draw the second vector and the resultant vector beside the first vector to avoid drawing on top of each other.
When motion is a straight line what do we do?
We often refer to one direction as positive and the other as negative direction. We don’t need to put arrows on the letter for this one because we are treating them more like scalars.
How do we represent time intervals? Or how to find change in time?
Tf - Ti = delta (triangle) t
Displacement
Change in position. Displacement comes from subtracting two vectors.
–> –> –>
detla D = Df - D
To find the average speed of something:
Vavg = distance travelled/
time interval
= d / delta t
Units for speed = m/s
Speed is a scalar
Velocity
–>
V
Units for velocity = m/s [direction in square bracets]
Velocity is a vector
To find somethings average velocity
–>
Vavg = change in position(displacement) /
time interval
–> –> –> –>
Vavg = delta d = Df - Di /
delta t = Tf-Ti
Difference between speed and velocity
Velocity has direction. If the motion is only in one direction, then the speed will be the magnitude of the velocity. There is a change of direction involved, then the magnitude of the displacement will be difference from the distance travelled, so the magnitude of the velocity will be different from the speed.
What happens if the velocity is constant?
The velocity at any time will equal the average velocity.
–> –>
V = delta d /
detla t
Cycle
When an object makes repeated motions, one complete motion is a cycle. This is just a count, has no units.
Period of repeated motion
The time required for one cycle. Symbol - 𝘛Units : seconds
Frequency of the repeated motion
The number of cycles in one second. Symbol : 𝘧
Units: Hz (hertz)
Hz is equal to 1/s or s^-1 since cycles are not actually units.
Why are frequency and periods reciprocals of each other?
Since the units for period and frequency are recipricals.
𝘧 = 1/T
or
T = 1/𝘧
On a graph what does the slope of the line joining the starting and ending points represent?
The constant velocity that would take the object from the starting point to the ending point in the same amount of time.
The formula for average velocity rearranged for final position :
–> –> –>
Df = Vavg x delta t + Di
What does this formula match to and how dos it relate to a graph of motion?
Exactly matches to
y = mx +b. Vertical intercept is Di, delta
t (horizontal value involved) = x, and slope is Vavg. Vertical value at the end of the time interval is Df.
