Mechanics Flashcards
Kinematics
Deals w/ description of motion (terminology?)
Distance (x/s)
- How far an object goes (unit: m)
- Scalar (no direction involved)
Displacement (x/s)
- Change in position of an object in a certain direction OR shortest distance an object covered in a certain direction
- Final position minus the initial position
- Unit: m (+ direction)
- B/c direction involved, vector
- Can be positive (right, forward, upwards, etc.) or negative (backward, left, downwards, etc.)
- “Displace” from initial to final position
Speed (v)
- Rate at which distance is covered
- Distance over time (x/t)
- Unit: ms^-1
- Scalar (direction not involved)
- Slope of a distance-time graph represents speed
Velocity (v)
- Change in position per unit time OR displacement per unit time OR speed in a certain direction
- Displacement over time (change in position [final minus initial] over time)
- Unit: ms^-1 (+ direction)
- Vector (has direction)
- Slope of a displacement-time graph represents velocity
*Rate = per unit time
*Post-slash = unit
*Speed, velocity interchanged
Distance-time/Displacement-time graphs
- “As the slope goes, so does the motion”
- Interpretation has a lot to do w/ slope (all about slope and then maybe a little based on the y-axis)
ex.
Slope = velocity
Straight line = constant
Line goes up = positive
Interpretation: The above graph represents an object whose speed is constant and positive and the distance increases proportionally (if line goes through origin).
- Displacement could be increasing sharply or gradually too (and velocity could be zero [displacement constant])
*“tending towards…” ex. t
*Whatever a graph w/ a horizontal line represents is zero
Area of a displacement-time graph
- We’re not doing calculations rn, but just try to figure out what area represents (triangle for diagonal and rectangle for straight line)
- Do you recognize the formula (does it represent anything useful)?
- Use units
Avg speed
- There must’ve been changing speeds (implied)
- Total distance over total time
Avg velocity
Total displacement over total time
Instantaneous speed
- Velocity at a certain point in time
- Draw tangent, make triangle (connect to axes): line must be blow curve
- Change in y over change in x
Acceleration (a)
- Rate of change of velocity
- Change in velocity (final [v] minus initial [u]) over time
- Unit: ms^-2
- Vector (has direction [uses velocity])
- Slope of a velocity-time graph represents acceleration
- Object is said to be accelerating if velocity increases or decreases or if the object changes direction
- Negative acceleration = decceleration
NOTE
- For circular motion, direction is not constant, so even though the speed is constant, there’ll be a change in velocity, and acceleration will be present
- If tangent a straight line, speed at that point is zero
- Speed and velocity can be interchanged, so speed can be negative
- More curve = more change in velocity = more acceleration
- When falls downward, change in position is negative
- Write all five?
- Vertical line = connection between whatever was happening before and what happened next
- No acceleration is x-axis
- Say “force of gravity” or “gravitational force” (not just “gravity”)
- Acceleration, force go together (if there’s acceleration, there’s force)
- Deep in space, force of gravity is 0?
- Outer space has a small amt of gravity b/c it’s close to earth?
- Negative sign is conventional (shows it’s going downward)
- Negligible = ignore (not present)
Area of a velocity-time graph
Represents distance (do the calculation)
Area of an acceleration-time graph
Represents speed (do the calculation)
Uniformly-accelerated motion (UAM)
- Motion of an object whose acceleration stays constant (ex. freely falling object, object moving in a straight line w/ constant acceleration, projectile [parabola], frictionless incline [there are inclines they can pad so that there will be almost no friction as the object falls and the only force acting on it would be gravity]], etc.)
- Weightless: only force present is gravity (no air resistance [so mass doesn’t matter])
- Negative symbol applies to force of gravity when falling (agrees w/ force): downward is negative for vectors
- For distance-time, a curve
- For acceleration-time, a straight horizontal line
- For velocity-time, straight line (diagonal) up/down (acceleration is a vector, so can be constant or negative)
- Negative acceleration b/c -d/t (-v)
*When you balance w/ normal force, that’s when something’s mass comes in
*Weight is gravity
