Chapter 3 - Motion Flashcards
What’s the difference between distance and displacement ?
Distance:
- The length of the path moved by an object
- scalar quantity
- SI unit = metre
Displacement:
What’s the equation for acceleration ? And is it a vector or scalar quantity ? What’s the SI unit ?
A = v-u/t
It’s a vector
SI = ms-2
What’s uniform acceleration ?
This is where the acceleration remains constant over a period of time
What’s the acceleration due to gravity ?
g = 9.81 ms-2 downwards
What does x equal in v = x / t ?
x = distance
What is the gradient of a displacement time graph ?
The gradient = velocity
In velocity time graphs, what does gradient = ?
Gradient = acceleration = change in V / change in t
In velocity time graphs, Whats the area underneath the curve = ?
The area under the line (curve) = displacement or in a speed time graph it would equal distance
What type of quantities are displacement, velocity and acceleration ?
They are all vector quantities so the direction matter as vectors have a magnitude and direction
What is speed ?
How fast something is moving, regardless of direction
What is displacement ( s ) ?
How far an object has travelled from its starting point in a given direction
What is velocity ( v ) ?
It is the rate of change of an objects displacement ( its speed in a given direction )
What is acceleration ( a ) ?
The rate of change of a objects velocity
What is average speed ?
Its the total distance covered over the total time elapsed
What is instantaneous speed ?
The speed of an object in any given point in time is know as instantaneous speed
What could acceleration mean ?
Acceleration could mean a change of speed or direction or both
What is uniform acceleration ?
It is constant acceleration
What are the 4 main equations that are used to solve problems including uniform acceleration ?
v = u + at
s = (u + v) / 2 x t
s = ut + 1/2 at *2
v2 = u2 + 2as
v = final velocity
u = initial velocity
a = acceleration
s = displacement
t = time
What is free fall defined as ?
The motion of an object undergoing an acceleration f ‘g’ = 9.81 ms*-2
Where does ‘g’ act ?
‘g’ acts vertically downwards
What’s the magnitude of ‘g’ ?
unless your given a different value then ‘g’ should be taken as 9.81*-2 though it varies slightly at different points on the earths surface
What’s the only force acting on a object when its in free fall ?
weight
Can objects have an initial velocity in any direction and still undergo free fall ?
Yes, as long as the force providing the initial velocity is no longer acting on the object
What can you replace a with in the equations of motion ?
you can replace a with g
what is ‘g’ ?
It is a constant acceleration
What are all of the sign conventions ?
g is always downwards so its usually negative
t is always positive
u an v can either be pos or neg
s can be either pos or neg
usually upwards is positive and downwards is negative but you can change this
what to do if there is no initial velocity - the object just falls ?
then you put u = 0ms*-1
and then all your equations will be changed a bit because 0 x something is 0
so for e.g.
v = ut + 1/2 at2 becomes v = 1/2 at2
Give a method to measure the acceleration due to gravity
what are the sources of error ?
1) measure the height from the bottom of the ball bearing to the trapdoor
2) flick the switch to simultaneously start the timer and disconnect the electromagnet, releasing the ball bearing
3) the ball bearing falls, knocking the trapdoor down and breaking the circuit - which stops the timer
4) use the time measured by the timer and the height between the bottom of the ball bearing and the trapdoor, to calculate a value for g using the formula h = 1/2 gt2
The most significant sources of error will be the measurement of the height - using a ruler you will have a uncertainty of about 1mm
also there is switch delay and air resistance
