Module 3 - Section 1 - Free Fall Flashcards
Under what conditions can free fall happen ?
And how is free fall defined ?
Free fall only happens if there is only gravity acting on the object and nothing else
Free fall is defined as ‘ the motion of an object undergoing the acceleration of gravity ( g ) ‘
In which direction does ‘g’ act and why ?
‘g’ acts vertically downwards - this is because ‘g’ is the acceleration due to gravity and acceleration is a vector quantity therefore it has a magnitude and direction
What is the magnitude of g ?
The acceleration due to gravity or ‘g’ is 9.81ms*-2
However it varies on different points on the earth
What’s the only force acting on an object when it’s in free fall ?
When an object is in free fall the only force acting on it is its weight
As weight = mass x gravity
Can objects have an initial velocity and still undergo free fall ?
Objects can have an initial velocity in any direction and still undergo free fall as long as the force providing the initial velocity is no longer get acting on the object
As for free fall to happen the only force that can be acting on the object is its weight
Explain an experiment used to measure ‘g’
1) Firstly measure the height, h from the bottom of the ball bearing to the trapdoor
2) Then flick the switch to simultaneously start the timer and disconnect the electromagnet, releasing the ball bearing
3) Then the ball bearing falls, knocking the trapdoor down which breaks the circuit, stopping the timer
4) Then use the height between the bottom of the ball bearing and the trapdoor and the time recorded on the timer to figure out the acceleration due to gravity ‘g’ - use the equation s=1/2at*2
This is taken from the equation s=ut+1/2at*2 however the initial velocity is zero so you can cancel the ut out as 0 x whatever is 0
What is the most significant source of error in the ball bearing practical experiment to find the value of ‘g’ ?
And how can you reduce this error ?
The most significant source of error in this experiment would be the measurement of height, h
Using a ruler you would have an uncertainty of 1mm
You can reduce this error in your measurement of h by using a set square ( the triangle ruler thing ) to make sure that your eye is level with the ruler
What do you have to assume in the experiment to measure ‘g’ ?
You have to assume that the effect of air resistance is negligible and that the magnetism of the electromagnet decays instantly
In motion equations what can you replace a=acceleration with ?
a —> can be replaced with ‘g’
In motion, generally speaking what direction is positive and what direction is negative ?
Generally speaking, upwards is positive (+) and downwards is negative (-)
In which direction does ‘g’ act and is it positive or negative ?
‘g’ always acts downwards so its USUALLY negative
Which one is positive and negative ?
u and v ?
t ?
s ?
U and v can be either positive or negative
T is always positive
S can be either positive or negative
What happens to the motion equations when there is no initial velocity ?
They all get shorter because when u = 0 then if something is multiplied by it then it will also become 0 so there is no point of including it
For example v = u + at —> v = at
And acceleration is just -9.81ms*-2
What happens to the motion equations when there is an initial velocity upwards ?
The motion equations are normal and don’t change
But a = -9.81ms*-2
What happens to the motion equations when there is an initial velocity downwards ?
For e.g. Alex throws a stone down a cliff. She gives it a downwards velocity of 2ms*-1. It takes 3s to reach the water below. How high is the cliff
We know that u = -2, a = -9.81, t = 3s
The answer will be -50 and negative because the stone ends up further down then when it started
But the height of the cliff would be 50m
