Module 3 Motion Flashcards
What is instantaneous speed?
It is the speed of an object during a specific point in it’s journey.
Define acceleration. Give si units
Rate of change of velocity. m/s^2
What part of a displacement time graph gives velocity?
What is area of speed time graph?
Gradient
Distance
How do you find acceleration from displacement-time graph?
Draw velocity-time graph from gradient of displacement-time graph and then the acceleration is the gradient of this graph
How to find average velocity and instantaneous velocity from a displacement-time graph?
The instantaneous velocity is to be found at a point where the displacement is increasing non-linearly.
Average velocity can be found by drawing a lobf to the the end point of the displacement time graph starting from the initial point of the graph.
Then find the gradient of this lobf.
(Since displacement is increasing non linearly this means the graph is a positive curve)
Draw a tangent to the appropriate point on the graph and find the gradient of this tangent
How is thinking distance related to initial speed ‘u’? Give formulae.
Thinking distance is the distance traveled while reacting to stimulus.
It is the product of the cars speed and the time taken to react ‘t’,
S(Thinking distance)= U* t
S is directly proportional to u
What would the work braking distance of a car be that is travelling twice the speed of a car going at X m/s.
State and define formulaes.
The braking distance is the distance travelled while braking.
Braking does work on the car given by,
Work done ‘W’= Force applied by brakes ‘F’ * Distance moved while braking ‘S’
FS= Kinetic energy of car
FS= 0.5* m x^2
As S is directly proportional to x^2
A 2x increase in speed would mean a 4x increase in braking distance
If you are given s and v, how can you calculate t for horizontal motion, using only 3 variables.
Explain why you can calculate horizontal t using this formulae and not vertical t.
You can use s=v/t -> t=v/s
We can use this equation for horizontal motion as usually acceleration a = 0 horizontally, meaning no air resistance.
Vertically there is always gravity acting on Earth causing acceleration ’g’.
What do light gates measure?
They measure how long their infrared signal is interrupted (processing is done in the data logger).
This can be used to measure velocity and acceleration
How to calculate speed of trolly from video analysis?
Set a point of reference, measure it’s distance from the starting point.
Check the frame rate of the camera then check in how many frames the trolly reaches the reference point. Use this info to figure out time travelled by trolley = 1/frame rate * frames taken to reach reference point
Then use the formulae: (distance/time)
What is constant in horizontal and vertical components of an object in motion?
Horizontally speed is constant (no drag)
Vertically acceleration by gravity is constant.
Why does vertical acceleration due to gravity not affect the horizontal component of motion?
Because acceleration is at right angles to horizontal motion.
