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
Describe the experiment (trapdoor, ball bearing), that can be used to find the value of g
Measure the height from the bottom of the ball bearing to the trapdoor
Flick the switch to simultaneously start the timer and disconnect the electromagnet, releasing the ball bearing
The ball bearing falls, knocking the trapdoor down and breaking the circuit - which stops the timer. Record the time
Explain how do find the value of g, from the data collected in the experiment (ball bearing)
You recorded the height, and time it takes the ball to fall that height
Plot a graph of height against time it takes the ball to fall, squared. Then draw a line of best fit
With constant acceleration: s = ut + at²/2
u = 0 if you drop the ball so
s = at²/2
so the gradient of the line of best fit = g/2
How can you increase the accuracy of the measurements you make, in the experiment to find the value g? ( Ball Bearing)
Use a small and heavy ball bearing so you can assume air resistance is so small that you can ignore it
Use a ruler with smaller increments and pick a certain point on the ball bearing to measure from to reduce the errors in measuring the height
Experiment to find g (Ball bearing):
How can you remove the random error that might arise if you timed the ball bearing manually by eye? What does this do to the uncertainty?
Using a computer automatically and time the ball bearing’s fall
Reduces the uncertainty in time measurement
How can you do a different experiment, to find g, using light gates to calculate the velocity?
Drop the ball bearing from a height h so it falls though the light gate. The light gate automatically calculates the velocity of the falling object.
Then use v² = u² +2as to find the acceleration due to gravity
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 how to investigate the motion of a trolley on a slope
Set up the experiment
Place the trolley on the ramp and line it up with the start line. Let go of it
The datalogger will record the time taken for the trolley to pass through the light gate and calculate the velocity of the trolley as it passes through the gate
Change the starting position of the trolley so d is varied
How does a ticker timer work?
They create holes in, or make dots on, a long piece of paper (ticker tape) at regular time intervals
How can you measure the the time taken for the trolley to go down the ramp using a ticker timer?
Attach ticker tape to the back of the trolley and thread it through the timer. Switch the ticket timer on when you release the trolley, and off when it reaches the end of the ramp. The time taken can then be calculated from the number of holes punched into the ticker tape
Describe uncertainties and accuracy when using ticker timers
Ticker timers are able to measure time very accurately but rely on manually turning on and off the machine, which will add uncertainty to the measurements, human error/reaction time. Uncertainty can also be introduced when having to count the total number.
Describe the accuracy of data loggers
They do not have human error, unlike ticker timers, and can calculate the velocity and display it in real time – saving time and allowing comparisons between experiments to be easily made
How can you investigate how collisions affect the motion of an air glider?
Measure the length and mass of both gliders
Turn on the video camera and start recording
Push one glider so that it hits the second glider
When both gliders have come to a stop, stop recording
What is the set up for the glider experiment?
Position a video camera side on to the motion of the gliders
Place two gliders on top of an air track and a meter rule next to it
What does the glider experiment investigate?
How mass and velocity of a glider just before collision affect the velocities of both gliders after the collision
How can you use the video, from the glider experiment, to calculate velocities?
Using video analysis software, you can view your videos frame by frame. Pick a point of reference on the meter rule and count how many frames it takes a glider to pass that point.
By knowing how many frames per second the video is shot it, you can calculate the time taken for a whole glided past that point. You recorded the length of each glider and so you can calculate their velocities
Briefly describe how iterative methods can be used for modelling displacement/velocity
Velocity and displacement are calculated over lots of small tiny increments to model their behaviour over a longer period of time
