Chalter 3 Flashcards
How do you find a cars true speed, what value you need to take
How do you do this
Have to take instantaelunludnspeed, which means close the time distance as much as you can
Distance time graph
Instantaneous speed?
Gradient = speed
Find a Rahmen of a curve and calculated speed here
Displacement time graph
Gradient velocity
Velocity time graphs
What do shape of lines mean
- gradient = acceleration
- displacement = area under (- area under negative )
, total distance = total are under
1) if straight then constant velocity
2) if straight up constant increasing velocity
3) if straight up curved = increasing velocity at increasing rate
If curved down = decreasing velocity at increasing rate
What gives something infinite acceleration?
Essentially what happens when you change direction to acceleration
If it changes direction without stopping, this means it will be x/0 which is infinity
- changing direction changes acceleration !.
HOW TO DESCRIBE Motion if an object on velocity time graph
Say whatever acceleration it si constant whatever
ALWAYS MENTION THE MOMENTARILY STATIONARY POINT
and then what happens after to
What is uniform acceleration and what can you do with that
Uniform acceleration is when a body changes its speed at a constant rate , while tracking in a STRAIGHT LINE
If not then it is variable and you can’t use DYNAMICS EQUATIONS WITH THEM
How to find acceleration if dynamic
Instsneous gradient
Little tricks and things for suvat
Remember that up is negative if getting slower down is positive whatever you lick you keep the same
If it says work out time if flight either do from when it satwitonsrynin air and multiply by two or remember the final velocity is - initial velocity so it becomes. -2 initial velocity basically
Remember what’s the acceleration for anything suspended in air (and what about if travelling from trampoline )
Always 9.81, the moment you’ve left trampoline resultant force is 0 and only affecting is gravity and so only gravity is acting when in air
What is stopping distance m thninking disrance and breaking distance
Stopping = thinking and breaking
Thinking distance is the distance travelled whilst reacting to having to stop = reaction time x speed and so is dependent on your reaction time and highest speed
Breaking distance is the distance travelled from moment breaks have been applied
What factors affect these and how to calculate
Thinking = reaction time and starter speed
Breaking = how good you’re breaks are, how good grip is on Tyree, icy road etc
You calaukte thid using SUVAT, as you are decelerating here
What is free fall
The action if a body accelerating solely due to gravity without a DRAG PRODUCING DEVICE
A=g
When do we ignore drag and when do we not
(2) situations when we don’t
- ignore if more than 3 orders of magnitude lower
- don’t ignore if BODY MASS is very small compared to surface area (essentially d/m ratio) like a feather
- or you are falling at a very high speed because d is proportional to v2
How to do experiment to calculate G PAG METHOD TICKER TAPE
1) Attach a tapper to a pong sheet of paper set at a sertain frequency , and then attach weights to the paper
2) let go , and count the number of dots that appear
3)multiply the number of dots by 1/f , and this gives you the time
4) measure the distance the dots went and this guved you s
Now use s = UT + 1/2AT2 to find A
How to find G using electormagnetic method? Trapdoor etc
1) a ball is attached to electromagnet dudpenedover a trapdoor. When current is turned off the magnet demagnetises so ball can drop and a timer is started
2) once the ball hits the trapdoor, electric contact is broken and thus the timer stops
Now can sue value for time, s as height and u to be 0 to find a
What are inaccuracies with the electric trapdoor experiment and how can you fix them
So
- time it takes for it to demagnetise is a slight delay from when the timer starts
- also air resistance causes a delay
To improvement
- use a heavier ball = less air resistance?
- and a LONGER DISTANCE so time error uncertainty don’t make much difference
How else can you reduce these uncertainties, what equipment
LIGHT GATES! And here detector starts and stops very accurately for the timer
How to do the taking pictures method
How to do this using a graph ?
Twke rapid pictures of a ball drilling nedr to ruler
Find values for how far it travelled and how long
Plot a graph of s against t2 due to formula
The gradient is = to 1/2g so multiply by 2
With air resistance when is the only time g is 9.81
At t=0 after thst the resultant force decreases and acceleration thus too
How to find final velocity basically
Find the time in one plane
Put it in other to find final velocity l
Basically if you have of both now use PYTHAGOREAN remember that’s always how you get it
REMEMBER AGAIN TI FALACUKRE FINAK VELOCITY HERE WHAT DO TOU NEED”
Pythagorean and then ANGLE AS IT IS A VECTOR
Remember you can do half time hack using when v= 0 as it stops in the sky
So basically make v is 0 when it momentarily stops, due to symmetry time will be double this so x2
Remember for projectile motion , if two objects have ONE COMPONENT THE SAME , will they land at the ground at the same time ?
WHAT CHANGES THEN!
YES, the thing linked between components is the time, so if both have one component the same then the time will be the same too!
What changes between components is FINAL SPEED and angle, as speed determined by mangintudes of sperrte velocities !
