Module 3 Projectiles Flashcards
What did Aristotle say about the speed of two falling objects of different masses
the heavier object would fall faster
What did Galileo say about the speed of two falling objects of different masses
reach the ground at the same time - same acceleration
How to remember who came first out of Galileo and Aristotle?
alphabetical: A before G
What does the gradient of the velocity time graph represent?
acceleration
Explain how the formula s=1/2(u+v)t is derived from the velocity time graph (other derivations needed too - see notes)
Use the idea average speed = distance over time
(u+v)/2 = s/t where u is starting velocity, v is final velocity
rearrange for s which represents displacement
When are SUVAT equations used?
when acceleration is constant - air resistance is negligible
Explain how you would use SUVAT equations
Resolve any vectors
write out SUVAT lists for vertical and horizontal
If an object is falling from rest at a given height, what do we know?
Just vertical motion so suvat vertically only
initial velocity is 0
acceleration is g = 9.81
distance travelled is height
What is the flight path of a bullet called?
a parabola
Why are horizontal components of velocity considered constant?
no horizontal forces acting, air resistance is negligible, so acceleration is zero
Describe how the vertical component of velocity changes over time for an object thrown upwards
From start to max height - vertical velocity decreases - acceleration in opposite direction to direction of velocity
At max height - vertical velocity is zero
From max height until just before end - vertical velocity increases in the opposite direction - acceleration is in the same direction as velocity
Describe the energy conversions that take place when an object is launched from the ground till it reaches the ground (in parabolic motion)
At start: KE is max, GPE is min
To max height: KE decreases and GPE increases
Max height: minimum KE (not zero is object is still moving horizontally), max GPE
Max to end: KE increases, GPE increases
End: max KE, min GPE
Why, at the maximum height of an object with parabolic motion, is KE minimum and not zero?
object still has horizontal velocity
horizonal component of velocity constant throughout
When is an object in free fall?
when it is accelerating under gravity with no other forces acting on it
Describe an experimental technique used to find g using an electromagnet
a switch in top of a circuit attached to an electromagnet is closed
circuit is attached to a trap door and a timer
an electromagnet is arranged above the trap door, a ball bearing is attached
When the switch is opened a timer is started and the ball bearing drops
opening the trap door which stops the same timer
What is the advantage of using the electromagnet technique to find g?
no human reaction time involved
What is a problem with using an electromagnet method to find g?
electromagnet may become magnetised and retain some of its magnetism - ball bearing won’t fall immediately
Measurement of height may not be accurate
Air resistance is ignored
Explain how a light gate can be used to measure g?
Set up two light gates above each other
Drop an object through the light gates (will give the time taken for the object to travel through each light gate)
Use the dimensions of the object to calculate U and V
Use v^2=u^2+2as and rearrange to find g which is a in this equation
What is a problem with using light gates to find g
They need to be lined up perfectly for an object to fall through both lightgates
Object needs to be big enough to be detected by both lightgates - causes a decrease in accuracy due to increase in surface area and therefore increase in air resistance and drag
How can a ticker timer and tape be used to find g?
Attach a piece of paper to a ticker timer and a falling object on the other end
Ticker timer marks strips of paper at equal time intervals
calculate the distance moved between each tick and use this to find average velocity
Plot a graph of average velocity for each section over time
gradient is acceleration, g
What is a problem with using a ticker timer to find g?
Paper may create resistance with ticker timer
INACCURATE measurement of distance between ticks on the paper
