8: Motion Flashcards
What is the difference between a scalar and a vector?
A scalar has no direction - it’s just an amount of something
A vector has a magnitude and a direction
How do you find the resultant vector?
Adding two or more vectors together
Define speed
How fast something is moving, regardless of direction
Define displacement
How far an object’s travelled from its starting point in a given direction
Define velocity
The rate of change of an object’s displacement (its speed in a given direction)
What is instantaneous speed?
The speed of an object at any given moment in time
What is the average speed?
Total distance covered, over the total time elapsed
What is another way of saying uniform acceleration?
Constant
Define free fall
The motion of an object undergoing an acceleration of ‘g’. Only gravity
What is/are the force(s) acting on an object in free fall?
Weight
Describe the rate of free fall for different objects
All objects free fall at the same rate
What is the main uncertainty in the experiments (light gates and trapdoor) to find the value g?
The height h
What is parallax, in the context of uncertainties?
Systematic error due to looking at the ruler at an angle
In a graph of displacement against time, how can you tell that something is accelerating?
Graph is curved
What does the graph (displacement against time), look like if the object is accelerating at a uniform rate?
Rate of change of the gradient will be constant
In a displacement time graph:
If there are two objects, both accelerating, how can you tell which is accelerating more?
Steeper curve
In a displacement time graph:
If there are two objects, both accelerating, how can you tell which is accelerating less?
Shallower curve
In a displacement time graph:
How can you tell if object is decelerating?
The line has a deceasing gradient - so more like √x graph
What does the gradient of a displacement time graph tell you?
The velocity
How do you find the instantaneous velocity of an object, using the displacement time graph?
Draw a tangent and calculate the gradient
What does the gradient of a velocity time graph show you?
Acceleration
Uniform acceleration is always a [ ], on a velocity time graph
Straight line
The steeper the gradient, the [ ] the acceleration
Velocity time graph
greater
What is the area under a velocity time graph?
Displacement
What shows that the acceleration is increasing on a velocity time graph?
Increasing gradient
What shows that the acceleration is decreasing on a velocity time graph?
Decreasing gradient
What do free-body force diagrams show?
Show a single body on it own
Which forces are shown on a free body diagram?
Forces that act on the body, but not the forces it exerts on the rest of the world
If a body is in equilibrium, the forces acting on it will be [ ]
Balanced
How do you find the resultant force on a body?
Add the vectors (of the forces) together
Describe the accuracy of data loggers
They do not have human error and can calculate the velocity and display it in real time – saving time and allowing comparisons between experiments to be easily made
Briefly describe how iterative methods can be used for modelling displacement/velocity
Velocity and displacement are calculated over lots of small tiny increments/intervals of time to model their motion over a period of time
problem with iterative models, example
graphs don't look realistic they assume no change occurs within the sampled time intervals (eg. if the calculation is applied at 5 second intervals, it is assumed that the motion is constant between 5 and 10 seconds).
how to improve iterative models
The accuracy of iterative models can
always be improved by decreasing the time interval.
what are vectors
quantities with both magnitude and direction
suvat equation not given in booklet regarding s u v t
s = (u+v / 2) * t s - displacement / m u - initial velocity / m/s v - final velocity / m/s t - time / s
overall stopping distance of a car
the sum of its thinking distance and braking distance
what can affect overall stopping distance of car and how
the speed of the vehicle; the faster it is travelling, the greater distance it will travel in the same time it takes for the driver to react, hence producing a
larger thinking distance. The car will also need to undergo a greater braking force, resulting
in an increased braking distance.
advantages of iterative modes
can be used for difficult calculus problems
how to calculate new value of v
a = Δv / Δt -> Δv = aΔt
how to calculate new value of s
v = Δs / Δt -> Δs = vΔt
how to calculate value of acceleration for iteration
a = 9.8 - kv^-² k = constant
how do thinking and braking distance increase with doubling speed
thinking distance doubles
braking distance quadruples because of:
average speed doubling
Δv has doubled from 30 to 60, time taken for deceleration has doubled
