Chapter 3 Flashcards
How can you get closer to instantaneous speed?
Closer the time interval, otherwise everything is normally an AVERAGE speed
Instsneous speed?
Velocity?
Gradient tangent
Again gradient of tangent
What gives something infinite acceleration?
If it turns around and switches direction of velocity completely!
- this because you cant find a time for this change so acceleration is change of velocity and it goes all the way
Change direction = accelerate
WHAT IS DISPLACEMENT ANYWAYS
Remember
It’s the MIMIUM DISTANCE BETWEEN TWO POINTS , SO IF IT IS CIRCLE, STRAIGHT LINE
-“ vector that travels directly between two points
What is acceleration
The rate if change if velocity
What is uniform acceleration?
When a body changes it’d speed at a constant rate, whilst travelling in a STRAIGHT LINE.
So like changes by 2ms every second
- rather if it changed different each second that’s variable and dynamics equations do not apply
How to find acceleration that is variable ?
Instantaneous gradient of velocity time graph
Displacement on velocity time graph?
Area
Velocity time graphs how to describe motion
Say acceleration or whatever
Always mention the stationary point at 0
Displacement / disrsnce for velocity time graph?
What do you have to remember
Displacement is area above - area below,
Distance is area above + area below
BE CAREFUL TO DRAW YKUR SHALES INKY WHERE THE DOTS CONNECT OR ANSWERS WILL BE WRONG
Suvat 4
S= Ut+ 1/2at2 S= 1/2 (U+V) t
V2=u2 + 2as
V=u + at
Another one in case?
S = vt-1/2at2
Important to remeber for SUVAT about acceleration direction
If by going your acceleration decreases (deceleration), then it will be negative 9.81
But if you are going down where acceleration is increasing, use positive 9.81
Now with acceleration there will always be final and initial velocity,
IMPORTANT FOR SUVAT TIME
If it says time of flight but inky wants halfway make sure to use half the time!
What about acceleration in Air due to gravity
If you pick one as direction it will ALWAYS BE CONSTANT, so doesn’t change direction, is never maximum or minimum or 9 but always 9.81
What is thinking , breaking and stopping distance
Thinking distance is distance travelled when driver is reacting and thinking about stopping
Breaking is the distance once driver actually hits breaks
Stopping is thinking + breaking
So how calculate thinking distance and what affects it
Factors affecting driver = drugs alcohol distraction tired etc
This is dependent on reaction time and speed
So if speed = distance/ time, distance = speed x reaction time
2) Thus higher speeds and higher reaction times = more distance
Breaking distance!
Here you are going from an injtsl velocity to final velocity of 0, so use SUVAT
Factors affecting braking
Weather conditions (icy etc)
Worn tyres
Good brakes
Bad roads
As these are factors affecting the car and its ability to brake in quick time
What is free fall
The fall of a body through a medium without a drag producing device
How is acceleration derived without any resistance ?
F= ma
A= F/M
The only force acting is the body weight
A= W/m
A= mg/m
A= G = 9.81
Thus an object released into the earth will accelerate at 9.81 if no Over force is acting on it
What about with resistance
A= F/m
A=W-drag/M
A= mg/m -d/m
A=g- d/m, the DRAG MASS RATIO
Thus it is on the drag mass ratio that depends
Why do we ignore drag?
When do we not
Thus you can use SUVAT
It is normally 3 orders less than our weight
However we don’t when
1) body mass is very small compared to its surface area (LIKE A FEATHER)
2) A body is falling at a considerable velocity (like parachutist) because then drag is there (increase velocity = increase drag^2)
How to do experiment to calculate g
1) attach weights to tapper which hits a mark at a steady frequency
2) let go, measure the distance dots went and count them multiply by 1/f to get time
3) you can now do suvat with #= ut +1/2t2 and get g
